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Effect of pH on ammonia production by renal mitochondria

Tannen, Kunin — 1976-12-01

NH3 production by renal cortical mitochondria was studied under conditions of metabolic acidosis induced in vivo and with pH manipulations of the media bathing mitochondria from normal rats. A HCO3- medium equilibrated with O2 and CO2 was utilized with glutamine concentrations of either 10 or 0.5 mM. With chronic acidosis NH3 production increased significantly at either substrate concentration. Similar results were obtained with rotenone in the media, both with chronic acidosis and with acidosis of 3 h duration, indicating that increased glutamine entry and/or phosphate-dependent glutaminase (PDG) activity accounts for the increased ammoniagenesis. In contrast to acidosis induced in vivo, mitochondria from normal rats subjected to a diminution in medium pH, either by manipulation of HCO3 concentration or PCO2, significantly decrease NH3 production. Mitochondrial studies with rotenone, as well as studies of solubilized PDG, suggest that a low pH diminishes NH3 production by directly altering PDG activity. Furthermore, regardless of the specifics of the mechanism, these studies indicate that adaptation to metabolic acidosis is not the immediate, direct result of a change in pH.

Persistence of febrile response to pyrogens after PO/AH lesions in squirrel monkeys

Lipton, Trzcinka — 1976-12-01

Observation of a patient who developed fever in spite of severe CNS sarcoidosis led us to test the idea that febrile responses require mediation by neurons in the preoptic/anterior hypothalamic (PO/AH) region. Changes in rectal and skin temperatures and oxygen consumption were recorded after intravenous and intracerebroventricular injections of endotoxin, after intracerebroventricular prostaglandin E1 (PGE1), and after intravenous injections of leukocyte pyrogens in animals in which the PO/AH region had been destroyed. The capacity to develop fever persisted after PO/AH destruction, and the patterns of heat production and heat loss were unchanged. Pyrogens were still effective after intracerebroventricular 6-hydroxydopamine and intraperitoneal reserpine given to reduce brain amines in monkeys with PO/AH lesions. It is unlikely that a secondary control in the medulla oblongata is responsible for the persisting sensitivity to pyrogens, since multiple injections of endotoxin into this region did not cause fever either before or after the PO/AH region was destroyed. The results do not support the idea that control of fever is localized in the PO/AH region alone. Rather, it appears that in the brains of primates there is either multiple central representation of fever control or an inherent capacity to develop sensitivity to pyrogens and to produce coordinated febrile responses.

Ionic pathways of secretory membrane of frog gastric mucosa in Cl--free media

Holloman, Schwartz, Dinno, Carrasquer — 1976-12-01

Experiments were performed to determine the return ionic pathways of the secretory membrane of frog gastric mucosa associated with the electrogenic H+ pump in Cl--free media. The replacement of a 52 mM Na2SO4 secretory solution with a 52 mM K2SO4 secretory solution led to a decrease of resistance, an increase of the H+ secretory rate, and a reversal of the PD. The replacement of 52 mM Na2SO4 with 52 mM MgSO4 led to an increase of resistance and a decrease of the H+ rate. These results provided evidence for the existence of K+ and Na+ pathways, the former having a lower resistance than the latter. Short-circuiting the mucosa in Mg2+ solutions increased the H+ rate to the value in Na+ solutions, hence ruling out the possibility that Mg2+ might interfere with the H+ pump. The fact that the Mg2+ secretory solution, without K+ or Na+, did not abolish the H+ rate suggested the presence of at least a third ionic pathway. presumably SO42-, providing that Mg2+ does not penetrate the mucosa.

Glycogen levels and peripheral mechanisms of glucose-induced spppression of feeding

VanderWeele, Skoog, Novin — 1976-12-01

Rabbits deprived of food for 0, 2, 4, 6, 8, 16, and 24 h were assessed for glucose-induced feeding suppression, refeeding after deprivation, and liver glycogen. In previous research, we hypothesized a relationship between liver glycogen and the transition from duodenal to hepatic glucose suppression. In duodenally cannulated rabbits, the infusion of 10 ml of isotonic glucose in awake, free-feeding animals significantly suppressed food intake but did not do so in those food deprived for 2, 4, 6, 8, or 24 h. In hepatic-cannulated rabbits, similar amounts of glucose significantly suppressed food intake in 4-, 6-, 16-, and 24-h-deprived animals. Also, refeeding after deprivation increased as a function of continued deprivation until 6 or 8 h, when refeeding reached asymptote, or decreased through 24-h deprivations. In agreement with these observations, liver glycogen showed a sharp decline between 4, 6, and 8 h of deprivation (depending on circadian cycle). It is proposed that liver glycogen depletion, or some correlate, alters liver glucostatic regulation and determines refeeding after deprivation.

Inhibition of transmembrane K transfer in ureter-ligated dogs infused with KCl

Hiatt, Chapman, Davidson, Sheinkopf, Miller — 1976-12-01

In anuric dogs loaded with K by infusion with 2 meq KCl/kg per h until prelethal hyperkalemic cardiotoxicity appears, the extent of transmembrane K transfer depends on the origin of the anuria. Animals with bilateral ureter ligation transfer a mean of 1.2 meq/kg to intracellular fluid, while those with bilateral nephrectomy transfer more than 2.5 times as much (3.1 meq/kg). Further, if dogs with functioning kidneys are ureter ligated or nephrectomized after approximately 45 min of K loading, K transfer ultimately falls as infusion continues. The fall is precipitate and over 90% in ligated animals; but it is gradual, and only 10% in those that are nephrectomized. Finally, K transfer, because of the absence of insulin, is negligible in K-loaded pancreatectomized dogs with bilateral ureter ligation, but fairly substantial in pancreatectomized animals with bilateral nephrectomy. The data suggest that ureter ligation and hyperkalemia activate a renal mechanism that interferes with the transfer of infused K to intracellular fluid. The mechanism may involve the renin-angiotensin II-aldosterone system to a limited degree.

Washout kinetics of red cells and plasma from the spleen

Levesque, Groom — 1976-12-01

Radioiodinated (125I) serum albumin was injected inttravenously in cats and allowed to equilibrate in the circulation. Red cell and plasma washout from the isolated spleens were enrom the isolated spleens were then compared during perfusion with oxygenated Ringer solution, the respective concentrations in the outflow being measured by celloscope and scintillation counters. Washout kinetics yielded three exponential components for cells (perfusate volumes for 50% washout (V1/2) being 0.067, 4.70, and 97 ml/g spleen) but only two for plasm (V1/2, 0.14 and 2.40 ml/g). There is no plasma counterpart to the slowly released cells, i.e., they do not represent a separate vascular space. This is an accord with a previous view that these are immature cells, delayed through adherence to fine structures of the red pulp. Compartment analysis indicates that the plasma and two remaining cell components represent washout from two separate vascular spaces, containing 0.09 ml/g blood at arterial hematocrit 37% and 0.42 ml/g blood at hematocrit 75%, perfused by 0.9 and 0.1 of the arterial inflow respectively. Evidence suggests these spaces are i) blood vessels, and ii) red pulp.

pH environmental of red cells in the spleen

Levesque, Groom — 1976-12-01

Intrasplenic pH in vivo was deduced from measurements on blood drained from cat spleen during contraction with the inflow occluded. The pH of blood in the red pulp is normally 7.20, but stasis or reduced flow through the pulp causes pH to fall toward 6.8. The splenic pulp contains blood of high hematocrit. To evaluate the role of buffering by the red cells themselves, intrasplenic p/ in red cell-free spleens was, therefore, estimated atering and leaving the spleen during red cell washout. At inflow pH less than 6.8 the outflow pH was raised, at inflow pH = 6.8 there was no change, b,t at inflow pH greater than 6.8 the outflow pH was lowered. These results indicate that the pH environment of red cells in the spleen results indicate that the pH environment of red cells in the spleen results from the interplay of two separate factors: i) pH-determining elements of the splenic tissue that buffer at 6.8, and ii) buffering provided by red cells passing through the pulp.

Relationships between resting tension and mechanical properties of papillary muscle

Templeton, Adcock, Willerson, Nardizzi, Wildenthal, Mitchell — 1976-12-01

The influence on mechanical properties of changes in resting tension over a range from 0.5 to 4.5 g was investigated in 12 isolated cat papillary muscles. At each resting tension, the muscles contracted isometrically with the exception of an externally applied sinusoidal stretch of 0.5% Lmax (deltaL) and 20 Hz. Stiffness (deltaT/deltaL) was determined from deltaL and the peak amplitudes (deltaT) of the individual cycles from the sinusoidal component of tension. Assuming that the muscle and experimental apparatus behaved as a linear second-order mechanical system, it was possible to divide stiffness into its elastic and viscous components. During rest, total stiffness and its components were linearly related to tension. During contraction, stiffness and its elastic component were linearly related to tension. Furthermore, increasing resting tension increased the intercept and decreased the slope of this linear stiffness-tension relationship. The relationship between viscous stiffness and tension during contraction is more complex in that it is a direct relationship at low resting tensions, but an inverse one at high resting tensions.

Contributions of pressure and flow sensitivity to autoregulation in mesenteric arterioles

Johnson, Intaglietta — 1976-12-01

The relative influence of presence and flow on dilation of arterioles with pressure reduction was examined in preparations of cat mesentery. Erythrocyte velocity and diameter were measured in individual arterioles during stepwise reduction in mesenteric arterial pressure. Volume flow was calculated from velocity and diameter data. Approximately half of the arterioles which dilated with pressure reduction also showed an increase in volume flow. In a second series of experiments, a graded reduction of flow in single arterioles was produced by local downstream occlusion. Graded occlusion caused dilation. In a third series, flow in single arterioles was completely stopped by downstream occlusion, and arterial pressure was then lowered. Most arterioles dilated with pressure reduction. In a fourth series, flow in the total preparation was completely stopped and static intravascular pressure set by a reservoir. Elevation of static pressure typically produced arteriolar constriction. We conclude from these studies that the mesenteric arteriole is sensitive both to intravascular pressure and flow, with the former probably more important than the latter in the phenomenon of autoregulation.

Nephron function of the isolated perfused rat kidney

De Mello, Maack — 1976-12-01

Nephron functions of an improved isolated perfused rat kidney preparation were studied by micropuncture techniques. Single-nephron glomerular filtration rate (SNGFR), intratubular pydrostatic pressures (IP), transit time (TT), and the reabsorption (R) of H2O, Na, Cl, and K were measured in superficial proximal (PT) and distal tubules (DT) of the preparation. Mean SNGFR was 27.2 nl/min and 25.2 nl/min when measured in PT and DT, respectively. The PT transport functions were well maintained throughout the perfusion (mean values were: IP, 14.3 mmHg; TT, 17.7 s; fractional (F) RH2O, 64%; absolute RH2O, 15.4 nl/min; FRNA, 66.5%; FRK, 71%, and tubular fluid-to-perfusate tf/p) ratio of Cl, 1.37). The short loops of Henle reabsorbed less than 10% of the load of H2O and Na delivered to them and the TF/P ratio of electrolytes in the earliest DT segments were high (TF/P)Na = 0.88, (TF/P)Cl = 1.27, and (TF/P)K = 1.11). This deficiency in function of Henle's loop explains, at least in part, the degree of natriuresis of the preparation (overall FRNa = 97.5%). Transit time to end DT was prolonged (82.3 S) and IP in DT elevated (14.9 mmHg). The DT was able to compensate, in part, for the overload from Henle's loop by reabsorbing 36% of the fluid load and 54% of the Na load delivery to it. We concluded that the improved isolated perfused rat kidney is a suitable preparation with which to study several aspects of renal function, particularly proximal tubules transport functions.

Sustained pressore responsiveness to prolonged hypothalamic stimulation in awake rats

Bunag, Riley, Montello — 1976-12-01

Whether or not pressor responsiveness changes in unanesthetized rats during recurrent sympathetic excitation was determined by recording blood pressure and heart rate continuously while the posterior hypothalamus was stimulated repeatedly with constant currents. Because preliminary tests showed that telestimulation with a radio-controlled stimulator produced erratic responses, awake rats were routinely stimulated in a conventional manner by connecting them through wires to a square-wave stimulator. Although tachycardia was the most common chronotropic effect, bradycardia also occurred, and both responses were occasionally seen in the same rat at different times. Inhibition of chronotropic responses by combined pharmacologic blockage with propranolol and atropine did not affect corresponding pressure responses in normotensive rats. Renal and spontaneously hypertensive rats always had larger pressor responses than normotensive ones, and, in spite of individual variations, responsiveness generally remained unaltered during 3-6 h of repeated hypothalamic stimulation. These results indicate that in awake normotensive or hypertensive rats cardiovascular responses to posterior hypothalamic stimulation continue unabated even when stimulation is repeated for hours.

Glucose transport in isolated perfused proximal tubules of snake kidney

Barfuss, Dantzler — 1976-12-01

Glucose transport was studied in isolated, perfused snake (Thamnophis spp.) renal tubules. When 14C-labeled and unlabeled glucose concentrations for bath and perfusate were identical, net transepithelial glucose transport occurred from lumen to bath. Maximum rates of transport were 1.24 X 10-12 and 2.17 X 10-12 mol min-1 mm-1 in proximal-proximal and distal-proximal segments, respecitvely. Glucose concentration in cells of perfused tubules of both segments was less than that of bath and lumen when tubules spontaneously stopped transporting glucose. Transepithelial glucose permeability ath leads to lumen) was about 0.25 X 10-5 cm sec-1 for both segments. Peritubular membrane permeability (bath leads to cell) was about 0.50 X 10-5 cm sec-1 for both segments. Luminal membrane permeabilities (cell leads to lumen) were 0.29 X 10-5 and 0.65 X 10-5 cm sec-1 for proximal-proximal and distal-proximal segments, respectively. Luminal membrane permeability in opposite direction (lumen leads to cell) was about 10.0 X 10-5 cm sec-1 for both segments. These results indicate that, during maximum glucose absorption, glucose enters cells down concentration gradient across luminal membrane by a mediated process and is transported out of the cells against concentration gradient at peritubular membrane.

A role for glucose in hypothermic hamsters

Resch, Musacchia — 1976-12-01

Hamsters undergo hypothermia when exposed to a mixture of 80% helium and 20% oxygen at low ambient temperatures. The hypothermic hamster, rectal temperature (Tre) 7 degrees C, becomes hypoglycemic, and reversal of hypoglycemia is effected with glucose infusion. Hypothermic hamsters at Tre 7 degrees C showed a fivefold increase in survival times from 20 to 100.5 h when infused with glucose which maintained a blood level at about 45 mg/100 ml. A potential role for osmotic effects of the infusion was tested and eliminated. There was no improvement in survival of 3-O-methylglucose or dextran 40-infused animals. The fact that death eventually occurs even in the glucose-infused animal after about 4 days and that VO2 undergoes a slow decrement in that period suggests that hypothermic survival is not wholly substrate limited. Radioactive tracer, [U-14C]glucose, showed that localization of the 14C, was greatest in brain tissue and diaphragm, intermediate in heart and kidney, and lowest in skeletal muscle and liver. The significance of the label at sites important to respiration and circulation was presented.

Na-K-ATPase localization in teleost urinary bladder by [3H]ouabain autoradiography

Renfro, Miller, Karnaky KJ, Kinter — 1976-12-01

Previous studies on the urinary bladder of the seawater-acclimated winter flounder (pseudopleuronectes americanus) demonstrated that active Na and Cl transport were ouabain sensitive. This suggested a relationship between the Na pump and Na-K-ATP-ase. The specific binding of [H]ouabain to Na-K-ATPase provides a means of localizing the site of active Na transport. In isolated bladders, a positive linear correlation (r= 0.89) was found between the active Na transport rate and the Na-K-ATPase activity. Ouabain binding by the bladder surface appeared to be saturable and relatively specific, e.g., was reduced by a high K concentration. When only the mucosal side of the bladder was exposed to 5 muM ouabain, both inhibitory effects and binding were small and are explained by finite permeability of the bladder to ouabain. In contrast, binding and inhibitory effects from the serosal side were much greater. Autoradiographs demonstrated that [3H]ouabain was bound only to the serosal side of the epithelial cells. Ultrastructural examination revealed that the area of ouabain binding coincided with the basal and lateral plasma membranes.

Tubuloglomerular feedback: effect of dietary NaCl intake

Kaufman, Hamburger, Flamenbaum — 1976-12-01

Response to angiotensins I and II and to AI-converting-enzyme inhibitor in a shark

Opdyke, Holcombe — 1976-12-01

The spiny dogfish shark, which does not have renal juxtaglomerular cells, exhibits a strong pressor response to both angiotensin I and II. A nonapeptide, angiotensin I-converting-enzyme inhibitor, blocks the pressor response to angiotensin I in this fish. The pressor response to both angiotensin II and norepinephrine is completely blocked by the adrenergic blocking drug phentolamine.

Lithium-induced diuretic effect of antidiuretic hormone in rats

Dousa, Barnes — 1976-12-01

The effect of a low dose of lithium (1 meq/kg per day) on renal function and its response to antidiuretic hormone (ADH) was studied in unanesthetized rats. This dose of lithium itself had no influence on renal water and electrolyte excretion, but lithium-treated rats responded paradoxically to exogenous ADH by increases in urinary volume, excretion of total solutes, sodium, potassium, and phosphate. Administration of ADH in the presence of lithium led to a lowering of urine osmolality, but free water clearance was not significantly reduced. Adenylate cyclase from the renal medulla of animals treated with ADH and lithium had a lower response to synthetic vasopressin in vitro than in animals treated with lithium alone. The results suggest that exogenous ADHis diuretic in the presence of a low concentration of lithilm. The predominant mechanism for this diuresis is probably inhibition of electrolyte and isomotic water reabbsorption in various nephron segments, including those proximal to the collecting ducts. ADH also markedly increased urinary excretion of lithium and appears to promote accumulation of lithium in the renal medulla.

Effect of graded doses of cortisol on total body calcium in rats

Yasumura, Ellis, Fairchild, Brook, Cohn — 1976-12-01

Male rats with an average body weight of 250 g were injected (sc) daily for 4 wk with 0.05, 0.20, 0.75, or 3.00 mg of cortisol acetate. Intact and adrenalectomized control animals were injected daily with 0.1 ml of vehicle (corn oil). Total body calcium (TBCa) was measured weekly in each rat by in vivo neutron activation analysis. The gain is body weight of rats treated with 0.75 mg cortisol was significantly less than controls, and the animals treated with 3.00 mg cortisol lost weight. In spite of these differences in body weight, the TBCa of all rats increased to an equal degree from an average of 1.93 g to 2.81 g in 4 wk. In addition, there were no significant differences in tibial ash calcium. However, calcium (mg) per unit length (mm) of tibia was increased in rats treated with the higher doses of cortisol; thus bone density was increased. These results demonstrate that the TBCa increases even when rats are subjected to cortisol. This is explained in part by the normal rate of intestinal calcium absorption in cortisol-treated rats.

Acid-base regulation in pregnancy

Lim, Katz, Lindheimer — 1976-12-01

Plasma bicarbonate decreases during normal pregnancy. To assess what roles increased extra cellular volume or alterations in parathyroid hormone levels (iPTH) have in the maintenance of this decrement, we evaluated acid-base metabolism in eleven 3rd-trimester women. Base-line pH and PCO2 were 7.44 and 27.3 mmHg, respectively. Mean tubular reabsorption of phosphate was 93% and baseline iPTH levels were similar to those of nonpregnant subjects. During the slow infusion of hypertonic NaHCO3, a urinary threshold of HCO3- (THCO3) appeared at a mean plasma level of 18.9 meq/liter, but as plasma HCO3- increased progressively, its renal reclamation was almost complete and there was no evidence of either splay or tubular maximum, even when filtered loads of HCO3- reached 5 meq/min. Urine acidification was normal and distal [H+] secretory ability( deltaidification was normal and distal [H+] secretory ability (delta urinary PCO2) was similar to that reported in nongravid subjects. In metabolic balance studies blood pH and plasma HCO3- increased (P less than .01 and less than .02, respectively) when the women changed from a high- to a low-sodium diet. Mechanisms by which decreased plasma bicarbonate levels are maintained during gestation are discussed.

Effect of hypermagnesemia on rat jejunal sodium and water transport

DiBona, Sawin — 1976-12-01

Hypermagnesemia decreases sodium and water reabsorption in the rat renal proximal tubule. To further understand this action, the effect of hypermagnesemia on sodium and water transport in the in vivo perfused rat jejunum was studied. The rat jejunum was chosen as another transporting epithelial tissue in the same species with unidirectional sodium flux characteristics similar to the rat renal proximal tubule, i.e., leaky as opposed to tight. Hypermagnesemia decreased net jejunal sodium and water reabsorption. This decrease was due to a reduction in unidirectional sodium efflux from lumen to blood and not to an increase in unidirectional sodium influx from blood to lumen. Hypermagnesemia did not change the jejunal permeability to inulin. The effect of hypermagnesemia on jejunal sodium and water transport is similar to that renal proximal tubule sodium and water transport. This similarity suggests that the mechanism of action of magnesium of these two transporting epithelial tissues is similar.

Hemodynamic pulmonary edema in dogs with acute and chronic lymphatic ligation

Magno, Szidon — 1976-12-01

The effect of lymphatic ligation on relative lung water (g H2O/g dry lung) was studied in dogs. Raising left atrial pressure to 20 mmHg for 2 h in chronically lymphatic-ligated dogs (4 days) caused a significantly greater increase in relative lung water than the same hemodynamic challenge did in sham-operated and acutely lymphatic-ligated dogs. There was no significant difference in relative lung water between the acutely lymphatic-ligated and sham-operated dogs. At normal left atrial pressures, there was no significant difference in relative lung water between the sham-operated and chronically lymphatic-ligated dogs. Since the combined effects of chronic lymphatic ligation and left atrial hypertension is greater than the sum of the individual effects, it appears that chronic lymphatic ligation increases the susceptibility of the lung to hemodynamic edema, we suggest that chronic lymphatic ligation may have produced increases in the interstitial volume and protein mass that are undetectable by our technique. These increases, in turn, could lead to a reduction in tissue safety factors against hemodynamic pulmonary edema.

Ion transport across isolated antral mucosa of the rabbit

Fromm, Schwartz — 1976-12-01

Isotopic fluxes of Na, Cl, and K were measured across isolated antral mucosa under short-circuit conditions. HCO3 fluxes were also measured with either isotopic and/or pH-stat methods. Net secretion of all four ions was observed. HCO3 secretion is due to a transmural process requiring metabolic energy. Secretion of endogenous HCO3 was not observed, and the unidirectional mucosal-to-serosal flux of HCO3 was negligible. There appears to be a close relationship between HCO3 secretion and the unidirectional mucosal-to-serosal Cl flux, but not relationships were observed between the unidirectional serosal-to-mucosal flux or either unidirectional Na flux. The bulk of HCO3 secretion is independent of the unidirectional Cl fluxes, but there is a fraction of HCO3 transport that is dependent on unidirectional Cl transport. However, HCO3 transport is not measurably influenced by inhibition of net Cl (and Na) transport per se.

Dietary self-selection following subdiaphragmatic vagotomy in the white rat

Fox, Kipp, VanderWeele — 1976-12-01

Nineteen female Wistar rats were employed in a self-selection-of-diet study assessing the effects of vagotomy on macronutrient consumption. Nutrients offered were a 30% sucrose solution, a 15% casein hydrolysate solution, and olive oil. In addition, noncaloric bulk, vitamins, and water were allowed. Bilaterally, subdiaphragmatically vagotomized rats showed a significant decrement in carbohydrate ingestion and daily total caloric intake (P less than .05 in both comparisons). Fat and protein intakes were unreliably altered. It is hypothesized that the vagus nerve relays glucose absorption and/or storage information from the periphery to the brain (perhaps lateral hypothalamusy, and hence, vagotomy produces carbohydrate-intake decrements, specifically. The decrement could also be explained as resulting from efferent effects of vagotomy such as decreased gut hormonal release.

Central antihypertensive effects of inhibitors of the renin-angiotensin system in rats

Sweet, Columbo, Gaul — 1976-12-01

The possibility that mean arterial pressure (MA) might be maintained by an effect of angiotensin II or its precursors on the central nervous system in rats made hypertensive by occluding the aorta between the renal arteries was investigated. Aortic coarctation produced severe hypertension (MAP greater than 150 mmHg) and plasma renin activity values (radioimmunoassay) at least 10 times normal within 2-6 days after surgery. [Sar1, IIe8]angiotensin II, an angiotensin II antagonist administered centrally via an intracerebroventricular (icv) injection (10-100 mug), lowered the MAP in a dose-dependent manner. Peripheral administration of [Sar1, IIe8]angiotensin II (bolus injection) at 100 mug intra-arterially was ineffective, but the antagonist did lower arterial pressure when infused intravenously for 1 h at 4 times this dose. Less than Glu-Trp-Pro-Arg-Pro-Gln-Ile-Pro-Pro, a converting enzyme inhibitor, and pepstatin, a renin inhibitor, were ineffective via an icv injection. These results suggest that angiotensin II is in part responsible for the elevation in blood pressure following aortic coarctation in rats. Both central and peripheral administration of [Sar1, Ile8]-angiotensin II lowered mean arterial pressure but the antagonist lowered arterial pressure at lower doses and produced a more rapid decline in arterial pressure when administered into the central nervous system then when administered intra-arterially or intravenously.

Influence of oxygen and glucose on the water and ion content of swine aorta

Harrrison, Massaro — 1976-12-01

The swelling properties of isolated swine arterial tissue have been studied to determine their effect on diffusion and hydraulic permeability measurements. Tissue potassium and sodium content were also measured to obtain an index of tissue metabolic activity. When oxygen and glucose were present in the incubation medium, a 5% decrease in tissue water content was observed over an incubation period of approximately 3.5 h. Under these conditions the tissue potassium content was higher and the sodium content was lower than when oxygen and/or glucose were omitted from the medium. When both oxygen and glucose were omitted, the potassium and sodium levels were significantly altered, suggesting a disturbance in the sodium-potassium transport system due to depletion of necessary metabolities.

Extracellular space of swine aorta measured with [14C]inulin and [14C]sucrose

Harrison, Massaro — 1976-12-01

Measurements of the extracellular space (ECS) of the isolated swine thoracic aorta were performed with both [14C]inulin and transient measurements and appeared to have better access to available tissue water than the [14C]sucrose gave more consistent results in available tissue water than the [14C]inulin. With [14C]sucrose as the tracer, no significant difference in the ECS was found when the tissue was incubated for 1.5 h in the presence of oxygen and glucose as compared to an incubation in which both oxygen and glucose were absent. However, the ion contents were markedly altered by this change in incubation medium. When oxygen and glucose were present tissue K+ was significantly higher and tissue Na+ was significantly lower than when these metabolites were deleted from the medium. Thus, significant alteration in ion content did not lead to substantial cell damage or bursting.

In vivo control of mitochondrial enzyme concentrations and activity by oxygen

Mela, Goodwin, Miller — 1976-12-01

Newborn and adult dog heart mitochondria were prepared from animals chronically adjusted to varying arterial oxygen tensions. Similarly, rat liver and heart mitochondria were isolated from animals acutely exposed to lowered inspired oxygen. After isolation, all mitochondrial samples were assayed under normoxic conditions. These experiments illustrated the following effects of oxygen on mitochondrial function: 1) respiratory activity in State 3 or in the uncoupled state increased after hypoxia and decreased after increased in vivo oxygenation; 2) similarly, the turnover of cytochrome oxidase increased in hypoxia and decreased after increased oxygenation; 3) after chronic hypoxia cytochrome oxidase, cytochrome c and b concentrations decreased per miligram of mitochondrial protein; 4) all mitochondrial preparations were well coupled and exhibited normal capabilities to perform oxidative phosphorylation. The data are interpreted to indicate sensitive control of mitochondrial respiratory capacities by oxygen in vivo.

Characterization of leucine transport by toadfish liver in vivo

Persell, Haschemeyer — 1976-12-01

Kinetic analysis of L-leucine uptake by toadfish liver at 20 degrees C in vivo has been carried out after pulse injection of L-[14C]leucine into the hepatic portal vein. D-[3H]mannitol, which is taken up slowly by toadfish liver, is used as a marker for extracellular space and space accessible by simple diffusion. At normal plasma leucine concentration (0.1 mM), leucine uptake occurs rapidly (t1/2 = 0.25 min), representing a flux of 0.6 mumol/min for the liver as a whole. Analysis of the distribution of radioactive leucine among intracellular and extracellular free pools and protein-bound form at times of 30 s to 5 min after injection is consistent with operation of a concentrative or uphill transport system accounting for 40% of uptake at normal plasma concentration. Saturation of uptake occurs at increasing leucine loads; calculation of intracellular pool dilution from protein synthesis data indicates that 20-30% of liver intracellular space is occupied by incoming leucine during the first 2 min after portal injection. Maximal flux (V max) is 4.1 mumol/min per 7-g liver as a whole with Km = 0.6 mM. Competitive inhibition of leucine uptake is afforded by isoleucine and phenylalanine with lesser effects by aspartic acid, cysteine, methionine, threonine, tyrosine, and valine. No effect is observed with alanine, glycine, histidine, lysine, and proline.

Mechanism of pellet egestion in great-horned owls (Bubo virginianus)

Duke, Evanson, Redig, Rhoades — 1976-12-01

To study the mechanism of oral pellet egestion in great-horned owls, bipolar electrodes and strain-gauge transducers were chronically implanted in the esophagus, muscular stomach, and duodenum of six owls. Recordings from conscious owls plus simultaneous radiographic observations revealed characteristic gastrointestinal motility patterns associated with egestion. Beginning at about 12 min before egestion, gastric contractions formed the final shape of the pellet and pushed it into the lower esophagus. The pellet was moved out of the esophagus by antiperistalsis during the last 8--10 s before egestion. During pellet egestion, contractions of abdominal muscles were not detected. Pellet egestion appears to be unlike either emesis in mammals with a simple stomach or regurgitation in ruminants.

Regulation of avian insulin secretion by isolated perfused chicken pancreas

King, Hazelwood — 1976-12-01

Chicken insulin secretory responses to glucose, glucagon, tolbutamide, and lack of Mg2+ were measured using isolated perfused in situ chicken pancreata. Although elevating perfusate glucose concentration from 100 to 250 mg/100 ml failed to increase insulin release, 500 mg glucose/100 ml provoked a transient 5-min insulin response. Additionally, 700 mg glucose/100 ml resulted in both a transient response and subsequent elevation in secretory rate that continued throughout the following 50-min stimulatory period. Glucagon (500 microgram/ml) and omission of perfusate Mg2+ potentiated glucose-stimulated insulin output by 6 and 25%, respectively. A faster release of insulin (less than 1 min) occurred during tolbutamide infusion (0.13 mg/ml) than with either 500 or 700 mg glucose per 100 ml (2-3 min); however, secretory rates declined to near basal levels within 5 min. Mammalian-like insulin responses to glucose, glucagon, Mg2+ lack, and tolbutamide suggest similarities between avian and mammalian beta-cell insulin secretory mechanisms. Nevertheless, the relatively high chicken insulin release threshold and low insulin output to glucose indicate that chicken pancreata are relatively glucose insensitive.

Relationship of cerebral oxygen uptake to EEG frequency in isolated canine brain

Fitzpatrick, Gilboe, Drewes, Betz — 1976-12-01

Cerebral oxygen uptake was correlated with electroencephalographic (EEG) frequency and amplitude in 87 isolated canine brains. Group I (71 brains) was perfused with diluted blood and Group II (16 brains) was perfused with whole blood equilibrated with oxygen at various partial pressures. The EEG's were classified as follows: A, highest frequency greater than or equal to 17 Hz, alpha (8-13 Hz) amplitude less than 50 muv, delta (less than or equal to 3.5 Hz), amplitude less than 100 muv; B, highest frequency greater than or equal to 17 Hz, alpha amplitude greater to or equal to 50 muv, and/or delta amplitude greater than or equal to 100 muv. C, highest frequency 8-16 Hz, alpha amplitude greater than or equal to 25 muv, and delta amplitude greater than 100 muv, D, highest frequency 0.5-16 Hz, alpha, if present, amplitude less than 25 muv, and/or delta amplitude less than 100 muv, and E, highest frequency 0-16 Hz, alpha, if present, amplitude less than 10 muv, and/or delta amplitude less than 15 muv. The Group I oxygen uptakes in ml/100 g of brain per min+/-SE for the five EEG classifications were A, 4.39+/-0.06, B, 4.13+/-0.08, C, 3.76+/-0.09, D, 3.40+/-0.12, and E, 2.55+/-0.06, whereas the corresponding Group II values were A, 4.64+/-0.22, B, 4.28+/-0.15, C, 3.82+/-0.24, D, 3.39+/-0.40, and E, 1.38+/-0.42. As the EEG deteriorates, cerebral oxygen uptake tends to decrease in a significant and parallel manner in both the diluted and whole blood groups.

Independent secretion of different digestive enzymes by the pancreas

Rothman — 1976-12-01

Pancreatic secretion was collected from the cannulated duct of anesthetized rabbits during the perfusion of the upper duodenum with a balanced salt solution with or without 5 mM glucose. The secretion of amylase, chymotrypsinogen, trypsinogen, and total protein was measured. While glucose did not increase overall digestive enzyme secretion, it did change the proportions of the enzymes in secretion. In addition, the following was observed: 1) non-0,0 intercepts when the output of one enzyme was plotted against that of another (an enzyme-pair plot), 2) changes in the variance of the slope and intercept of enzyme-pair plots, and 3) an increase in the variance around the slope of an enzyme-pair plot, concurrent with a decrease in the variance around the slope of a plot for another enzyme pair that contained a common member. These observations suggest that different digestive enzymes can be secreted independently of each other.

Coronary intercapillary distance during growth: relation to PtO2 and aerobic capacity

Henquell, Odoroff, Honig — 1976-12-01

Intercapillary distance (ICD) was measured in left ventricles of rats beating in situ. Between 40 and 400 days of age, left ventricular weight increased threefold and ICD increased from 12.5-19.5 mum. ICD could be decreased by at least 2 mum at all ages studied. The number of capillaries which must be recruited to reduce ICD by 2 mum fell from 1,200/mm2 at 40 days to 280/mm2 at 400 days. Ventricular growth did not affect the O2 sensitivity of precapillary sphincters or the uniformity of capillary spacing. Calculations indicate that under basal conditions tissue PO2 (Pto2) in subepicardium is about the same at 40 and 400 days, even though VO2 per gram, capillary density, and ICD change twofold, twofold, and 7 mum, respectively. Nevertheless, as the ventricle grows, capillary recruitment becomes progressively less effective in defending Pto2 under conditions of stress. Diminished coronary capillary compensation for stress may, in part, account for the effect of age on the maximum aerobic capacity of the whole animal.

Parallel secretion of digestive enzymes by the in vitro rabbit pancreas

Steer, Glazer — 1976-12-01

Nonparallel discharge of digestive enzymes by the in vitro rabbit pancreas has been previously reported and this observation has been used to challenge the mass transport theory of enzyme synthesis and secretion by the exocrine pancreas. The current investigation reexamines the pattern of enzyme secretion from the in vitro rabbit pancreas. Secretion of alpha-amylase, trypsinogen, and chymotrypsinogen was studied from the unstimulated gland and from glands stimulated with either methacholine, cholecystokinin-pancreozymin, or the active octapeptide of cholecystokinin-pancreozymin. In all cases, only parallel discharge of alpha-amlyse, trypsinogen, and chymotrypsinogen was noted. These observations are consistent with the mass-transport theory.

Transepithelial transport kinetics and Na entry in frog skin: effects of novobiocin

Cruz, Biber — 1976-12-01

Na+ entry across the outer surface of frog skin and transepithelial Na transport were studied simultaneously at different [Na] in either the presence or absence of novobiocin by direct measurements of J12 (unidirectional uptake) and Io (short-circuit current). J12 consisted of two components: one linear, the other saturable. The kinetic parameters of the saturating components in controls were close to the kinetic parameters of overall transepithelial transport (Jm12 = 1.68+/-0.13 mleq cm-2h-1; Io =1.80+/-0.14 mueq cm-2h-1. K12 = 6.02+/-1.27 mM;Kio=6.12+/-1.33 mM). Novobiocin significantly augmented net transepithelial Na transport by increasing J13. J31 remained unaffected. A 1:1 relationship between the saturating component of J12 and Io was observed in both treated and untreated skins at all [Na] tested. (Jm12Iom, k12, and Kio were significantly larger in treated skins, but despite very drastic changes in transport rates, a close correlation between kinetic parameters of entry step and transepithelial transport was maintained. This suggests that the kinetics of transepithelial transport may simply reflect those of the rate-limiting step: the Na entry across the outer barrier of the skin. The results indicate that the linear component of J12 is not involved in transepithelial transport kinetics.

Effect of glycodihydrofuisidate on sulfobromophthalein transport maximum in the hamster

Delage, Dumont, Erlinger — 1976-12-01

The effect on sulfobromophathalein transport maximum (Tm) and biliary lipid secretion of sodium glyco-24,25-dihydrofusicate, a micelle-forming compound secreted into bile, has been studied in the hamster and compared to that of a physiological bile salt, sodium taurocholate. Biliary phospholipid and cholesterol secretion increased both during glycodihydrofusidate and taurocholate administration, an observation which suggest that both compounds increased th biliary secretion of micelle-forming compounds. In contrast, only taurocholate increased sulfobromophthalein Tm into bile, while glycodihydrofusidate administration decreased it. This observation suggests that the increase in sulfobromophthalein Tm observed during taurocholate administration is not the result of micellar sequestration. It could rather be the consequence of a specific effect of bile salts on the dye transport system.

Permeability of erythrocyte membranes

Hunter — 1976-12-01

Estimation of ENa from current-voltage curve

Li — 1976-12-01

Inner medullary plasma flow in the kidney with ureteral obstruction

Solez, Ponchak, Buono, Vernon, Finer, Miller, Heptinstall — 1976-11-01

To test the thesis that ureteral obstruction causes medullary ischemia, we determined inner medullary plasma flow (IMPF) in rats with bilateral or unilateral ureteral obstruction, and after relief of obstruction, by the intravenous 125I-albumin infusion technique. A progressive decline in IMPF was observed during obstruction of 18 h duration, greater in bilateral obstruction (7% of normal at 5h) than in unilateral obstruction (28% of normal at 5 h). The elevation in ureteral pressure was greater and more sustained in bilateral obstruction. After relief of obstruction, IMPF rose to 69-78% of normal in both groups within 2 h. Histologic studies showed tubular necrosis in portions of the inner and outer medulla immediately beneath the renal pelvic epithelium after bilateral or unilateral obstruction of 18 h duration, and India ink perfusion studies showed very poor filling of vasa recta in these areas. The concentrating defect in the postobstructive kidney may be related, at least in part, to damage inflicted by medullary ischemia during obstruction.

Hydrolysis of peptides within lumen of small intestine

Silk, Nicholson, Kim — 1976-11-01

The quantitative significance of intraluminal peptide hydrolases in the terminal stages of peptide digestion has been investigated, and the precise origins of these enzymes have been determined. Intestinal contents and mucosae were obtained from rats anethetized with ether. Experiments carried out on pancreaticobiliary secretions and germfree rats show that pancreatic and bacterial enzymes do not contribute significantly toward the luminal digestion of dipeptides. Chemical assay data, thermostability studies, and examination of electrophoretic mobilities of luminal peptide hydrolases indicate that jejunal enzymes originate predominantly from the cytoplasm of intestinal mucosal cells, whereas the brush border of muosal cells is a major source of the enzymes in the ileum. With glycl-L-phenylalanine and L-phenylalanyl-glycine as substrates, jejunal luminal activity was less than 2.6% of mucosal activity. Brush-border peptide hydrolase activity in ileal contents, however, was 11.9% and 40.7% of mucosal brush-border activity for the two substrates. Luminal enzymes thus play an insignifcant role in the terminal digestion of peptides in the jejunum, but have a much more important role in the ileal digestion of peptides.

Phosphorylation of cardiac regulatory proteins by cyclic AMP-dependent protein kinase

Reddy — 1976-11-01

Cardiac myofibrils were purified from canine myocardium, and the regulatory proteins (troponin + tropomyosin) were extracted and shown to contain endogenous cyclic AMP-dependent protein kinase activity. Other cyclic nucleotide stimulated the protein kinase activity but only at higher concentrations. The enzyme was able to catalyze phosphorylation of conventional substrates such as histones and casein as well as a component of the regulatory protein fraction with a molecular weight of 28,000 daltons. Endogenous phosphorylation required the presence of Mg2+ and was inhibited by Ca2+. A protein kinase inhibitor obtained from skeletal muscle inhibited the cyclicAMP-dependent phosphorylation. Escherichia coli alkaline phosphatase dephosphorylated the endogenous substrates. The level of phosphorylation found is severalfold higher than we have previously reported. A protein kinase, with its close association with the regulatory proteins, seems to be well suited to transmitting the message from the cyclic AMP to the regulatory proteins, a phenomenon that may influence the cardiac contractility via the troponin phosphorylation. The inhibitory effect of troponin on actomyosin might be changed by its state of phosphorylation.

Series elasticity of urinary bladder smooth muscle

Alexander — 1976-11-01

Loops of rat bladder were stretched between pins in vitro, supported by a clamp that could be suddenly shortened by activation of a solenoid to achieve a quick release of tension. The series elasticity measured in this fashion was found to follow an exponential course and to be modified by the rate of release, indicating a minor viscous component. Tissue length decreased and series elastic stiffness appeared to increase with muscle contraction, but no alteration in series elasticity was evident when the data were related to the tension existing in the tissue at the moment of quick release. Inactivation of the contractile system by removing calcium ion with ethylene glycol-bis-(beta-aminoethylether)-N,N'-tetraacetate (EGTA) similarly did not alter series elasticity when it was related to the tension existing in the tissue. Series elasticity during the stress relaxation following a stretch, and during the contracting and relaxing phases of rhythmic contractions, was also determined by tissue tension. The conclusion drawn is that contractile cross bridges do not contribute to the series elasticity measured in bladder tissue.

Penile pressures and muscle activity associated with erection and ejaculation in the dog

Purohit, Beckett — 1976-11-01

A needle-tipped polyvinyl catheter or subminiature pressure transducer was implanted in the corpus cavernosum penis (CCP), corpus spongiosum penis (CSP), or bulbus glandis to determine the pressure during coitus in 42 dogs. Silver ring electrodes were implanted in the ischiocavernosus (IC) and bulbospongiosus (BS) muscles to monitor the electromyographic (EMG) activity of these muscles. The CCP pressure increased from 26 mmHg in the quiescent state to 161 mmHg at mild erection of the penis in the presence of a receptive female. During the intromission phase of coitus, the mean peak CCP pressure was 5,296 mmHg in the dogs with implanted catheters and 7,434 mmHg in the dogs with implanted transducers. The CCP pressure peaks during intromission were more in phase with the contractile activity of the IC muscles than with the BS muscles. Anesthesia of IC muscles with lidocaine significantly reduced the CCP pressures and the dogs with low pressures were unable to copulate because of insufficient erection for intromission, which indicated that the IC muscles were the source of energy for the high CCP pressure. The mean peak CSP and bulbus glandis pressures during the intromission phase of coitus were 579 and 1280 mmHg, respectively. The contractile activity of the BS muscles was in phase with the CSP pressure peaks. Anesthesia of BS muscles with lidocaine reduced the peak CSP and bulbus glandis pressures during attempted coitus. The mean rupture pressure of the CCP was 86,615 mmHg.

Effect of temperature of resistance to stretch of tortoise muscle

Fowler, Crowe — 1976-11-01

The effects of temperature over the range 5-30 degrees on isometric contraction and resistance to mechanical stretches of the ramp and hold type applied to active muscle have been studied in isolated tortoise gastrocnemius muscles. The isometric tension decreases as the temperature is lowered but, when expressed as a proportion of the isometric tension, the change in tension at the end of the ramp phase of the stretch is increased at the lower temperatures. The proportionate tension change at the end of the hold phase of the stretch could not be directly related to the temperature. An attempt is made to interpret the results in terms of current opinions on the mechanism of the generation of muscular tension.

Properties of toad skin Na-K-ATPase with special reference to effect of temperature

Park, Hong — 1976-11-01

The NA-K-ATPase of toad skin was characteristically sensitive to Na, K, and ATP. It was not affected by amiloride, vasopressin, cAMP, and thyroxine, but stimulated by insulin. Ouabain, a potent inhibitor at 37 degrees C, did not inhibit the enzyme activity significantly at 23 degrees C. The optimal pH for the enzyme activity increased as temperature decreased. However, the optimal OH-/H+ ratio of the medium remained constant at 16 regardless of temperature. The Km for ATP remained unchanged between 37 and 8 degrees C if the OH-/H+ ratio was held constant at 16, but increased as temperature decreased if the pH of the medium was held constant at 7.4. The enzyme activity showed no appreciable variation between 37 and 20 degrees C with a constant OH-/H+ ratio of 16, whereas it decreased logarithmically at a constant pH of 7.4 over the same temperature range. These results indicate the presence of a typical Na-K-ATPase system in toad skin and that the enzyme is in the most active catalytic state at a fixed level of OH-/H+ ratio in the medium regardless of incubation temperature.

Age-related changes in Na+ excretion in saline-loaded spontaneously hypertensive rats

Mullins, Banks — 1976-11-01

The ability of 6- to 7-, 12- to 13-, and 16- to 17-wk-old spontaneously hypertensive rats (SHR) to excrete an acutely administered, isotonic saline load (equivalent to 4.5% body wt) was evaluated. Female SHR from two different colonies were studied. Age-matched female Wistar (W) and Wistar-Kyoto (WKY) rats served as controls. At age 6 wk, the fraction of administered Na+ load excreted by either SHR colony after 60 min was significantly lower than in the Wistar rats but not significank, one colony of SHR excreted significantly more sodium after 60 min than the other rats. Glomerular filtration rate during control periods was positively correlated with age in one SHR colony; no age-related changes were observed in glomerular function in the other groups. These data 1) suggest that WKY rats are more appropriate than the Wistar rats as controls for renal function in the SHR, 2) demonstrate that the ability of the SHR to excrete an acutely administered sodium load is equal to or greater than normotensive WKY controls, and 3) demonstrate that with respect to renal function parameters, the SHR is not a homogenous strain.

Effect of fasting on hepatic ligandin, Z protein, and organic anion transfer from plasma in rats

Stein, Mishkin, Fleischner, Gatmaitan, Arias — 1976-11-01

The effect of fasting on the rate of disappearance from plasma of bromsulphthalein (BSP) and dibromsulphthalein (DBSP), the hepatic content of BSP, and the concentration of ligandin and Z protein, two hepatic organic anion-binding proteins, was studied in the rat. Fasting for 48 h decreased the plasma disappearance of BSP and DBSP and the hepatic content of BSP as well as the amount of ligandin and Z protein. Phenobarbital given prior to fasting partially prevented these changes. A method of quantitation of Z by radioimmunoassay is described. Discrepancies in Z quantiation by dye binding and immunological methods in fasted but not control rats suggest the presence of competitors for organic anion binding to Z in fasting as well as after phenobarbital administration. Results of studies of ligandin turnover during fasting suggest decreased synthesis and increased degradation of the protein. Similar events may be of pathogenetic importance in nonhemolytic unconjugated hyperbilirubinemia observed during fasting in man, horses, and other animals.

Plasma glucagon in pups, decreased by fasting, unaffected by somatostatin or hypoglycemia

Hetenyi, Kovacevic, Hall, Vranic — 1976-11-01

In pups less than 4 days old, the mean basal plasma immunoreactive glucagon (IRG) level was about 3 times higher than in adult dogs. This high level decreased with age, and in pups older than 12 days the mean plasma IRG level did not differ from that in adults. Insulin-induced hypoglycemia did not raise plasma IRG concentration in young pups. Fasting decreased plasma IRG in young, but not in older pups. This decrease is consistent with the decrease in gluconeogenesis and in contrast to the metabolic adjustments observed in the adult organism. In pups less than 7 days old, both the pancreas and gastric mucosa contained considerably more IRG than the normal value reported for adult dogs. Gastroduodenal IRG was immunologically indistinguishable from pancreatic glucagon. In pups, somatostatin did not decrease the plasma concentration of either IRG or immunoreactive insulin (IRI) and caused no change in plasma glucose or in the rates of glucose production and utilization calculated from experiments with tracers. The experiments indicate that in pups the pancreatic and gastric alpha-cells are unresponsive to stimuli normally effective in grown dogs.

Kallikreinlike activity in perfusates and urine of isolated rat kidneys

Roblero, Croxatto, Garcia, Corthorn, De Vito — 1976-11-01

In the perfusate and the urine produced during perfusion of isolated rat kidneys a kallikreinlike enzyme similar to that found in the kidney was detectable by bioassay 15-25 min after the beginning of the perfusion. The source of the kallikrein activity was the kidney itself, since before the perfusion was started the blood remaining in the kidneys was washed out and the perfusion medium was free of kallikrein and its precursors and substrates. The kallikreinlike activity of the perfusate was characterized by a) an oxytocic effect on isolated rat uterus, b) a kininogenase activity on kininogen II, c) an esterase activity on N-benozyl-L-arginine ethyl ester, and d) a hypotensive effect on anethetized rats. These properties were inhibited by diisopropyl activity in the perfused kidney was lower than that in the nonperfused organ, but the total amount of kallikrein activity released to the excreted urine and the perfusate was significantly greater than the corresponding activity that disappeared in the kidney. This result is in keeping with the concept that the renal tissue is able to synthesize kallikrein.

Mechanical properties of rat cardiac muscle during experimental thiamine deficiency

Cohen, Abelmann, Messer, Bing — 1976-11-01

The intrinsic contractile properties of isolated left ventricular trabecular periods of 24, 40, and 53 days were compared with those from 35 weight-matched food-deprived animals and 25 ad libitum fed controls. Contraction mechanics were measured for each muscle when stretched to the peak of its length tension curve at 28 degrees C in oxygenated Krebs-Henseleit solution. Although both thiamine-deficient and food-deprived groups had a marked diminution in body and left ventricular weight in comparison to ad libitum fed controls, no differences in left ventricular weights from thiamine-deficient and food-deprived rats were observed. In comparison to ad libitum fed control animals, food-deprived rats exhibited a prolongation in the duration of muscle contraction and an augmentation of tension development after 40 days. Upon appearance of neurological signs at an average of 53 days of a thiamine-deficient rats exhibited a decrease in performance associated with a decrease in the duration of contraction and rate of tension development.

Regional shortening patterns in canine right ventricle

Raines, LeWinter, Covell — 1976-11-01

The right ventricular outflow tract (OT) is a functionally distinct area of the right ventricle. However, there is little information on the contrdingly, inflow tract (IT) and OT chords and right ventricular free wall segmental changes were measured with implanted ultrasound crystals. The timing and extent of shortening of IT and OT chords and free wall segments were determined both at rest and after stellate ganglion stimulation. At rest, IT chord shortening began 51 ms before OT shortening. OT expansion occurred during this period. IT chord shortening began 51 ms before OT shortening. OT expansion occurred during this period. IT chord shortening was 38% while OT shortening was 34%. In contrast, OT segments did not show systolic expansion. IT segment shortening was 13% while OT shortening was 21%. With stellate stimulation, IT-OT gradients of 15-25 mmHg developed. The lag between IT and OT shortening decreased to 30 ms and segmental shortening increased. We conclude that the OT is a physiologically distinct region which contracts later and remains contracted longer than the IT. Both septal and free wall movements contribute to these changes.

Effect of parathyroid hormone on renal tubular permeability

Lorentz — 1976-11-01

The effect of parathyroid hormone (PTH) on renal tubular permeability has been studied utilizing micropuncture techniques in the rat kidney. After microinjection into superificial nephrons during control conditions, inulin (98.8 +/- 2.7%) and mannitol (97.2 +/- 2.4%) recovery from the experimental kidney was essentially complete. During intravenous infusion of PTH, inulin (99.3 +/- 2.9%) recovery was again complete. Mannitol recovery decreased signficantly after both early-proximal (84.7 +/- 5.8%, P less than 0.001) and late-proximal (89.7 +/- 2.8%, P less than 0.001) injections. There was no loss of either mannitol or inulin following distal tubular injection. Late-proximal TF/P inulin ratios during control conditions were 2.10 +/- 0.20 and decreased insignificantly to 1.99 +/- 0.21 during PTH infusion. Late-proximal TF/P mannitol rations were 2.09 +/- 0.21 during control periods and during PTH infusion decreased significantly to 1.78 +/- 0.19 (P less than 0.001). These results indicate that PTH induces a change in proximal tubular permeability to a usually impermeable nonelectrolyte, mannitol. The effects of PTH on proximal tubular transport could be partially explained by this alteration in permeability, which would increase passive backflux of actively transported species and decrease net transport while having no effect on active transport.

Hepatic cell integrity in hypodynamic states

Carlson, Lefer — 1976-11-01

Changes in liver integrity were studied in isolated perfused cat livers during simulated shock conditions (i.e., combined hypoxia, acidosis, and ischemia) or under the influence of each hypodynamic state separately. The combined hypodynamic stimuli depressed carbon clearance 51% and significantly elevated lactic acid dehydrogenase (LDH) and cathepsin D activities in the perfusate. The perfused liver was more seriously affected by hypoxia than by acidosis or ischemia alone. Reticuloendothelial clearance was depressed 20% and 25% in acidosis and hypoxia, respectively. Hypoxia also induced a 3-fold increase in cathepsin D and a 13-fold increase in LDH activities in the perfusate. After 150 min of hypoxia or ischemia, free cathepsin D in liver tissue increased significantly. The impairment of liver cell integrity (i.e., of Kupffer and parenchymal cells) occurred between 60 and 90 min during simulated shock conditions, indicating that the liver is stable for 60 min when it is exposed to hypoperfusion. The perfused liver is sensitive to local stimuli that predominate in circulatory shock, particularly hypoxia. These stimuli promote the release of lysosomal and cytoplasmic enzymes as well as depress phagocytosis by the reticuloendothelial system, phenomena that exacerbate the shock state.

Inhibitory effects of catecholamines in canine cardiac Purkinje fibers

Posner, Farrar, Lambert — 1976-11-01

The effect of catecholamines over a wide range of concentrations was studied on 42K uptake and efflux, as well as on spontaneous rate in canine cardiac Purkinje fibers. Low levels of catecholamines (less than 10(-10) M epinephrine; less than 10(-9) M norepinephrine) decreased automaticity. This negative chronotropic effect was blocked by phentolamine and mimicked by phenylephrine. These low levels of epinephrine and norepinephrine also inhibited 42K uptake by Purkinje fibers but had no effect on 42K efflux. The inhibition of 42K uptake was blocked by phentolamine and verapamil and mimicked by phenylephrine. The data indicate an alpha-receptor-mediated negative response of rate and 42K uptake to low levels of catecholamine. The end result is discussed in terms of a competitive increase in the influx of Ca2+ rather than Na+ and an indirect inhibition of the Na+-K+ pump.

Effect of adrenal enucleation on sodium excretion in the rat

Alexander, Bengele, McNamara — 1976-11-01

After the adrenal glands are removed without their capsules, so-called adrenal enucleation, rats initially retain sodium, and, after adrenal regeneration, escape from salt retention. To define the renal mechanisms involved in this alteration in salt handling, we have utilized clearance and micropuncture techniques in three groups of saline-expanded rats that were sham-operated (S), enucleated (AE), or escaped after adrenal regeneration (E.) Sodium excretion was clearly blunted after AE, 5.5 mueq/min vs. 20.5 for S and 18.7 for E. Although glomerular filtration rate (GFR) and filtered load of sodium were lower in AE rats, the delivered load of sodium beyond the late distal tubule was not different among the groups: 0.30 neq/min for AE, 0.42 for S, and 0.40 for E. This was a consequence of strikingly greater sodium reabsorption in the loop of Henle and distal tubule in both the S and E rats. In the collecting duct over 50% of the delivered sodium was reabsorbed by the AE rats while over 30% of the excreted sodium was added in this tubular segment in the other groups. These data demonstrate that the impaired natriuresis after adrenal enucleation appears to be due to striking differences in collecting duct function. Since adrenal regeneration in the escape animals reverses this sodium retention, the effect is probably related to some alteration in adrenal hormone production. Sodium excretion in markedly expanded normal rats also appears to be determined by the net addition of sodium in the collecting duct.

Prostaglandin E release in the dog: effect of sodium

Terashima, Anderson, Jubiz — 1976-11-01

Renal arterial injections (20 ml) of 4 M NaCl in 8 dogs and of 0.5 M NaCl in two dogs were followed by significant but delayed increases over 60 min in renal venous prostaglandin E (PGE) concentrations as measured by radioimmunoassay. Perfusion pressure increased significantly only at 5 min but plasma sodium concentration remained above base line for 60 min. In two dogs in which renal artery blood flow was maintained at a constant rate, comparable increases in PGE concentrations were observed. Injections of 1 M mannitol in three dogs and 5% dextrose in water in two dogs did not result in significant changes in PGE concentrations. In four dogs, administration of 50 mg indomethacin 15 min prior to injection of 20 ml of 4 M NaCl abolished the changes of PGE concentration. Sodium appears to have an effect on stimulation of PGE release by the canine kidney. This phenomenon may be of physiologic significance.

Inhibition of ion transport by bile salts in canine gastric mucosa

Kuo, Shanbour — 1976-11-01

Studies were conducted with in vivo and in vitro canine stomach preparations. Instillation of 5, 10, and 20 mM bile salts in TES bufer (pH 7.4) into the nonsecreting stomach in vivo caused a progressive decrease in electrical potential difference (PD) and an increase in electrical resitance (R). The rate of acid secretion, determined by the pH-stat method in the histamine-stimulated stomach, decreased with 5 and 20 mM bile salts. Mucosal adenosine triphosphate (ATP) content of the nonsecreting or secreting stomach was reduced by bile salts. In vitro flux studies demonstrated that within the first hour after 1 mM bile salts were added to the mucosal side of the chamber, PD decreased, R increased, and net sodium transport decreased. In the second hour, unidirectional fluxes of sodium increased, indicating an increase in permeability of the gastric mucosa to sodium. These results demonstrate that the initial action of bile salts is inhibition of ion transport, which is followed by an increase in permeability.

Unidirectional uptake of iron across intestinal brush border

Sheehan — 1976-11-01

To define the significance of the uptake step by unidirectional uptake of iron was measured on proximal small intestintestinal segments from Nembutal-anesthetized rats. The method employed a nonabsorbable marker of adherent incubating medium, and the studies were performed during the linear time period of instantaneous uptake. Uptake was linear over the concentration range 0.1-10 mM, from three iron complexes. The rate varied with the bioavailability of the iron in each complex. The Q10 was 1.0-1.3. Uptake rates were similar in all segments of small intestine. Uptake was not increased in segments from iron-deficient animals or rats with hemolytic anemia. Cobalt did not inhibit the uptake rate. These studies demonstrate that the uptake of nonheme iron by the small intestinal mucosal cell is by passive diffusion and further indicate that the uptake step does not contribute significantly to the mucosal control of iron absorption.

Effects of hypoxia on cardiac growth in neonatal rat

Hollenberg, Honbo, Samorodin — 1976-11-01

To determine whether low oxygen environments enhance cardiac cell division in the neonatal period, newborn rat pups were reared for 21 days in 12-15% oxygen. Left ventricle and right ventricle weights were 30 and 180% greater than controls matched for body weight (P less than 0.001) as were left ventricle/body weight ratios (3.68+/-0.26 vs. 2.99+/-0.05 mg LV/g body wt,P less than 0.001). Left ventricular total DNA and DNA concentration was 95 and 48% greater than controls (P less than 0.001). Autoradiography confirmed that this increase in ventricular DNA resulted from an increased rate of division of cardiac muscle cells, fibroblast, and vascular endothelial cells. When [3H]thymidine was injected on day ), autoradiographs prepared on day 21 reflected an increased dilution of label in hypoxic rats consistent with enhanced proliferation. The labeling index and grains per nucleus of ventricular muscle cells was 25% (P less than 0.01) and 20% (P less than 0.02) less than controls, Thus, hypoxic stress applied early in the neonatal period augments the rate of division and ultimate number of cardiac muscle cells. Whether this enhancement results from a primary effect of oxygen or from secondary hemodynamic factors remains unknown.

Acute isovolemic anemia in anesthetized chickens

Nightingale — 1976-11-01

Acute isovolemic anemia was produced in anesthetized chickens by serial exchanges of 6% dextran 70 equal to 1% of body weight to quantitate cardiovascular and metabolic parameters. When hematocrit (Hct) and hemoglobin (Hb) levels were reduced by 50% (from 33.3 to 16.3 vol %, and from 10.3 to 5.4 g/100 g, respectively, P less than 0.001), tissue oxygen delivery was maintained by increases in cardiac output (CO), stroke volume (SV), oxygen extraction, and reduced total peripheral resistance (TPR). Heart rate, right atrial pressure, and oxygen consumption (Vo2) were unchanged. Further reductions in Hct and Hb (to 10.8 vol % and 3.7 g/100 g, respectively), were accompanied by cardiovascular failure, as evidenced by falling CO, SV, tissue oxygen delivery, and Vo2. Relative apparent viscosity determinations on the exchanged blood-dextran mixtures indicated that large viscosity changes occurred with the first exchange whereas subsequent exchanges had small incremental viscosity changes. These data indicate that in acutely anemic chickens, oxygen transport capacity was maintained by increased cardiac output and decreased peripheral resistance, unless the severity of the anemia resulted in cardiovascular failure.

Control of baboon limb blood flow and heart rate-role of skin vs. core temperature

Proppe, Brengelmann, Rowell — 1976-11-01

To discover the relative importance of body core temperature versus bodyskin temperature in raising limb blood flow and heart rate, we exposed seven unanesthetized, chaired baboons (Papio anubis) to a variety of heating protocols. First, the baboons were exposed to a 40-45 degrees C environment for 0.75-1.5 h. Arterial or right atrial blood temperature (Tbl), skin temperature (Tsk), mean right iliac blood flow (MRIF), and heart rate (HR) all increased gradually during heating. On the average, HR increased from 106 to 160 beats/min and MRIF rose to 286% of control level. To separate influences of Tbl and Tsk on cardiovascular changes, we manipulated Tbl and Tsk independently via a heat exchanger incorporated into a chronic femoral arteriovenous shunt. In most baboons, the MRIF and HR response to a hot environment could be essentially duplicated by elevation of bTbl with Tsk held neutral, while elevation of Tsk with Tbl held neutral had little effect. One baboon exhibited significant response to Tsk elevation with Tbl held neutral, although subsequent manipulation of Tbl overrode this response. We conclude that the normal response to heating in baboons is mainly attributable to drives from internal temperature-sensitive mechanisms. Elevated Tsk shows large effects only in exceptional cases.

Protein composition of lung fluids in anesthetized dogs with acute cardiogenic edema

Vreim, Snashall, Staub — 1976-11-01

We measured the protein composition of plasma and lung fluids from nine dogs with cardiogenic edema. To produce the edema, we increased left atrial pressure an average of 36 cmH2O by inflating a balloon catheter in the left atrium, infusing norepinephrine, and infusing large volumes of saline or saline-diluted blood. Blood samples were collected every 15 min, and airway fluid was collected from five dogs that developed severe edema. Terminally, the chest was opened and the lungs were removed. Samples of alveolar fluid were taken from the excised lung by direct pleural puncture with micropipettes. The lungs were frozen in liquid nitrogen and samples of free interstitial fluid were taken from the perivascular and peribronchial cuffs. Plasma and lung fluids were analyzed for total protein by the Lowry method and for albumin-globulin fractions by cellulose acetate electrophoresis. The average total protein concentrations (g/100 ml) were--plasma, 2.65; free interstitial fluid, 1.05; alveolar fluid, 1.23; and airway fluid, 1.29. The average albumin fraction of plasma was 0.40; of alveolar fluid, 0.43; and of airway fluid, 0.43. The protein concentrations in the three lung fluids were nearly identical to each other, but were less than half that of plasma. We conclude that in high-pressure pulmonary edema with alveolar flooding, the capillary endothelium retains the ability to restrict protein relative to fluid filtration, but the alveolar epithelium becomes freely permeable to protein.

Increase in resting tension of tracheal muscle due to rigor during metabolic inhibition

Bose — 1976-11-01

Resting tension of canine tracheal smooth muscle increased when glucose and oxygen were withdrawn from the bathing medium. Similar treatment of muscle stimulated with carbachol caused first a relaxation and then a secondary increase in tension. The increase in tension due t0 metabolic inhibition, unlike normal tracheal contractions, was insensitive to calcium depletion, was not associated with an active state, and was accompanied by marked reduction of tissue adenosine triphosphate, creatine phosphate, and glycogen content. Because muscle stiffness was also increased we concluded that hypoxic glucose-free contracture is due to rigor and not to an increased tissue calcium level as has been previously suggested. Rigor shortening during lightly loaded isotonic conditions is better maintained than rigor tension during isometric conditions. Our results also indicate that rigor tension is reduced irreversibly on imposition of a load and, therefore, the load-extension relationship during rigor in smooth muscle should be studied by making only small load changes.

Left ventricular function during acute elevation of aortic blood pressure in dogs

Ilebekk, Thorvaldson, Kiil — 1976-11-01

Cardiac responses to mechanical constriction of the aorta proximal and distal to the arch arteries and to intravenous infusion of angiotensin were examined in open-chest atropinized dogs during continuous recording of left ventricular and aortic dimensions by means of ultrasonic elements. Proximal constriction reduced stroke volume by 18% both before and during isoproterenol infusion without changing left ventricular end-diastolic pressure, dimensions, or contractility, (dP/dt)IP; angiotensin induced less pronounced increments in stroke volume and end-diastolic volume. By combining proximal constriction with saline-dextran infusion, stroke volume and end-diastolic volume increased as during distal constriction. These results indicate that differences in preload account for the differences in stroke volume responses to proximal and distal aortic constriction. We propose that increased preload is caused by redistribution of blood from capacitance vessels rather than retention secondary to cardiac decompensation.

Inhibitory effect of ethacrynic acid on chloride permeability

Motais, Cousin — 1976-11-01

Ethacrynic acid inhibits anion movements in ox red blood cells. The I50 for chloride is 7 X 10(-6) M. The inhibitory effect is instantaneous and completely reversed by washing the cells with a Ringer solution, suggesting that reaction with a membrane SH group is not involved in this process. Direct proof that ethacrynic acid does not act by its reactivity with thiol groups is given by experiments with dihydroethacrynic acid, a derivative that lacks the ability to combine with SH groups: the characteristics of inhibition are strictly identical (instantaneous and reversible; I50 equals 9 X 10(-6) M). All the phenoxyacetic derivatives tested were also more or less inhibitory. The relative activity of all the derivatives was highly correlated with their liposolubility, indicating that hydrophobic interaction is important in determining drug effect and influence of steric factors is minimal. The data suggest that inhibition essentially results from a hydrophobic interaction between ethacrynic acid and apolar regions of the membrane protein allowing chloride transport.

Metabolism of ketone bodies by ovine brain in vivo

Kammula — 1976-11-01

Ketosis was produced by intravenous infusion (5 mmol/kg per h) of [3-14C]acetoacetate (sp act 0.5 muCi/mmol) into fed and 7-day-fasted sheep. Changes in arterial and sagittal sinus blood samples. During acetoacetate infusion, there was a significant increase in ketone body uptake (P less than 0.001) and conversion to 14CO2 in both fed and fasted sheep. Changes in arterial concentrations and cerebral removal of various metabolites were investigated by simultaneous collection of arterial and sagittal sinus blood samples. During acetoacetate infusion, there was a significant increase in ketone body uptake (P less than 0.001) and conversion to 14CO2 in both fed and fasted sheep when compared to control periods (saline infusion). The percent conversion of ketone bodies to 14CO2 was slightly higher in fasted sheep (22%) compared to fed sheep (18%). Blood glucose and free fatty acid concentrations were decreased, but there was a significant increase in blood lactic acid and lactic acid production by the brain. The plasma insulin concentration was increased significantly both in fed and fasted animals. These results indicate that ovine brain can utilize ketone bodies irrespective of nutritional state. In addition, ketone bodies stimulated the production of lactate by ovine brain.

Effect of ethyl adenosine on myocardial flow after coronary artery occlusion

Hellmann, Pitt — 1976-11-01

The effect of ethyl adenosine-5'-carboxylate hydrochloride (EA) was determined in 17 dogs by the radioactive microsphere technique. In both experimental and control animals, microspheres were injected 5 min before (preocclusion period), 60 min after (occlusion period), and 75 min after (saline or vasodilation period) ligation of the left anterior descending coronary artery (LAD). Ten seconds prior to the third microsphere injection, saline was administered to five control animals, and saline with 0.5 mg/kg of EA was given to 12 experimental animals. There was no significant change in myocardial blood flow after saline injection. After EA, mean arterial pressure fell 10% (P less than .001); myocardial blood flow increased 275% (P less than .001) in the nonischemic left circumflex artery (CIRC) area and increased 82% (P less than .01) in the occluded LAD area. In addition, those animals with extensive collateral development showed a significantly greater increase in collateral blood flow than those with minimal collateral development (P less than .05). Thus, EA may increase flow to ischemic areas of myocardium dependent upon the extent of preexistent collateral supply.

Calcium-dependent resistance to stretch and stress relaxation in resting smooth muscles

Siegman, Butler, Mooers, Davies — 1976-11-01

Mechanical responses to stretch and length-tension relations were examined in rabbit taenia coli, mesenteric vein, aorta, and myometrium and in guinea pig taenia coli made atonic by incubation in Krebs-bicarbonate solution at 20-22 degrees C. When stretched 10% of the length at which maximum active tension is observed (Lo) in 0.5 s, the muscles showed a transient large force (resistance to stretch) that decayed to a new constant level within minutes (stress relaxation). The resistance to stretch decreased markedly in Ca2+-free [disodium ethylene glycolbis-(beta-aminoethylether)-N,N-tetraacetic acid (EGTA)] Krebs but was restored in normal Krebs solution. Calcium removal did not affect the passive length-tension curve. The absence of Ca2+ did not change the steady-state force maintained by the muscle; thus stretch resistance was not due to tone. Blockade of Ca2+ influx associated with electrical activity with 5-[3,4-dimethoxyphenethyl)methylamino]-2-(3,4,5-trimethoxyphenyl-2-isoprop ylvaleronitrile (D-600) and of Ca2+ release from intracellular sites with thymol (1 mM) completely blocked contraction but did not alter the responses to stretch, thus dissociating the responses to stretch from these processes and tension development. The Ca2+-dependent stress relaxation showed a dependence on muscle length similar to that for active tension development. Except at long muscle lengths, where connective tissue markedly affects length-tension relations, most of the "viscoelasticity" of these smooth muscles is dependent on calcium and may be largely due to the straining of crossbridges that are attached, but not generating a net force, in the resting state.

Rigor and resistance to stretch in vertebrate smooth muscle

Butler, Siegman, Davies — 1976-11-01

Depletion of the APT content of the rabbit taenia coli muscle to 0.07 mumol/g caused an increase in force equal to 11% of maximum active tension (Po) when the muscle was bathed in a calcium-containing Krebs solution at 21 degrees C, but no increase in force in a calcium-free solution. Stimulation of the muscle in calcium-containing medium during the loss of ATP increased the force maintained and permitted demonstration of an increased stiffness by shortening of the muscle. There was no increase in resistance to stretch in the ATP-depleted state compared with the resting state. There was, however, a calcium-dependent resistance to stretch with properties that suggested the presence of attached crossbridges in the resting state. Bathing of the resting muscle in a calcium-free medium decreased the resting resistance to stretch and permitted demonstration of an increased resistance to stretch in the rigor state. It is concluded that the rigor state exists in vertebrate smooth muscle.

Blood flow to respiratory, cardiac, and limb muscles in dogs during graded exercise

Fixler, Atkins, Mitchell, Horwitz — 1976-11-01

The distribution of cardiac output was analyzed in six dogs, with the animals at rest and running on a level treadmill for 3 min at 3-4 mph (mild exercise) and 3 min at 6-8 mph (moderate exercise). Organ flows were measured using 25-mug-diam radioactive microspheres. Cardiac output averaged 2.5, 4.6, and 5.7 liters/min, for rest, mild exercise, and moderate exercise, respectively. The greatest change was in diaphragmatic flow which increased by 275% with mild exercise and 500% with moderate exercise. Flow to intercostal muscles increased by 160 and 186%, to the exercising gastrocnemius muscle by 153 and 224%, and to cardiac muscle by 57 and 109% during mild and moderate exercise, respectively. Renal and cerebral flows did not change significantly. Significant decreases in flow occurred in the small and large intestines during moderate exercise. It is concluded that the increase in cardiac output during submaximal exercise was redistributed in a manner which limited flow to the brain, intestines, and kidneys and increased flow flow to the diaphragm, heart, and limb muscles.

Properties of immobilized guinea pig hindlimb muscles

Maier, Crockett, Simpson, Saubert CW, Edgerton — 1976-11-01

Guinea pig hindlimbs were unilaterally immobilized at resting length to evaluate histochemical, biochemical, and contractile properties of immobilized muscle. Contralateral limbs remained unrestrained. Four weeks later contractile properties were measured under chloral hydrate anesthesia. Average time-to-peak tension of the immobilized soleus was 30% less, whereas that of the gastrocnemius was not significantly changed relative to contralateral muscles. Immobilized soleus muscles acquired as much as 25% fibers with high alkaline myofibrillar adenosine triphosphatase activity; these fibers do not occur in the normal muscle. Neither the immobilized soleus nor gastrocnemius fatigued more quickly than their contralateral counterparts. In the immobilized gastrocnemius myofibrillar protein (mg/g muscle) decreased to 76% and maximum tetanic tension to 70% of contralateral values. However, tetanic tension per gram wet muscle weight or 100 mg myofibrillar protein was significantly greater in the immobilized gastrocnemius. No specific factor responsible for the increased tetanic tension could be identified.

Pentose cycle activity of the isolated perfused rat lung

Bassett, Fisher — 1976-11-01

Pentose cycle activity was estimated in isolated rat lungs under varying conditions of glucose oxidation. Lungs were perfused for 100-120 min with a Krebs-Ringer-bicarbonate buffer, pH 7.4, containing 1-14C- or 6-14C-labeled glucose and ventilated with 95% O2:5% CO2. Based on 14C specific yields in either 14CO2 or perfusate lactate plus pyruvate, pentose cycle flux in control lungs was 5.3 mumol of glucose per hour per gram dry weight (11-12% of glucose utilization). Pentose cycle activity was unaltered by perfusion with 0.8 mM 2,4-dinitrophenol. Perfusion with phenazine methosulfate, an artificial hydrogen acceptor, resulations of the pentose cycle based on 14C yields in tissue lipids (both the fatty acid and deacylated fractions) gave values 2-3 times higher than measurements based on 14CO2. This study indicates that pentose cycle activity in the lung accounts for a significant fraction of glucose utilization and this pathway readily responds to metabolic perturbation.

Regulation of plasma calcium in rats: age-related roles of PTH and calcitonin

Kalu, Foster — 1976-11-01

To determine the influence of aging on the relative roles of parathyroid hormone (PTH) and calcitonin in the control of calcium homeostasis during fasting, we assessed changes in plasma calcium in fasted rats following simultaneous removal of the glands that secrete both hormones. Animals ranging in age from 3 to 34.7 wk were thyroparathyroidectomized or sham operated and bled by orbital puncture prior to and 1.5, 3, and 6 h after surgery. After thyroparathyroidectomy (TPTX), plasma calcium fell immediately and progressively in very young rats (3-6 wk old); in young animals (6.5-9.4 wk old), there was a delay of about 1.5 h pceded by a rise, which persisted for at least 3 h. Since the rise and fall in plasma calcium after TPTX are most likely due to calcitonin and PTH deficiencies, respectively, our observations are consistent with the following hypothesis; in the fasting state, the relative importance of calcitonin and PTH in the regulation of plasma calcium varies with age; PTH appears to play the dominant role in young rats; however, during maturation the importance of calcitonin appears to increase progressively.

Effect of methionine sulfoximine on glutathione and amino acid levels in the nephron

Brehe, Chan, Alvey, Burch — 1976-11-01

The effect of L-methionine-DL-sulfoximine (MSO) on renal glutathione concentration and aspartic acid transport has been studied by analyses of parts of individual freeze-dried glomeruli, early and late proximal convoluted, early and late proximal straight, and distal straight and convoluted tubules, and patches from thinlimb and papilla areas. Glutathione normally varies threefold along the kidney nephron, being highest in the convoluted and early straight proximal tubule, lowest in the distal straight tubule. Large loads of aspartate cause 20% diminution of glutathione in outer cortex, due entirely to changes in proximal tubule segments. MSO alone lowers glutathione 90% in all parts of the proximal tubule, with no change elsewhere. MSO does not affect the large increase in aspartate in proximal tubules caused by saturating aspartate loads, suggesting that glutathione is not directly involved in transport of this amino acid. Aspartate loads cause a large increase in renal glutamine, which is especially marked in the proximal straight tubule. MSO effectively blocks this increase and depresses tissue glutamine below normal levels.

Effect of prostaglandin synthetase inhibitors on renal blood flow in the rat

Finn, Arendshorst — 1976-11-01

Using a small-diameter electromagnetic flow transducer, the effect on the autoregulation of renal blood flow (RBF) of two structurally different prostaglandin synthetase inhibitors, indomethacin, 4 mg/kg BW, and meclofenamate, 5 mg/kg BW, was studied in nondiuretic rats anesthetized with either the oxybarbiturate, sodium pentobarbital, or the thiobarbiturate, Inactin. Regardless of the anesthetic agent, RBF remained relatively constant above a perfusion pressure of 105 mmHg. Treatment with either indomethacin or meclofenamate had no measurable effect on the autoregulatory response. Each agent, however, resulted in an increase in the renal vascular response to exogenous angiotensin II, an effect consistent with prostaglandin synthetase inhibition. Base-line RBF was significantly reduced by indomethacin or meclofenamate only in those animals that had previously received angiotensin. These results support the hypothesis that, in th rat, autoregulation of RBF occurs independently of prostaglandin activity, but that a relationship does exist between the renal vascular actions of angiotensin II and prostaglandins.

Effect of acetylcholine on Cl- and Na+ fluxes across dog tracheal epithelium in vitro

Marin, Davis, Nadel — 1976-11-01

Electrical potential difference is generated across canine tracheal epithelium by active transport of Cl- toward and Na+ away from the lumen. The present study examines the effects of acetylcholine on short-circuit current, potential difference, resistance, and fluxes of 36Cl and 24Na measured across pieces of canine tracheal epithelium mounted in Ussing-type chambers. Under short-circuit conditions, acetylcholine (5 X 10(-5) M) increased significantly net ion flux toward the lumen of Cl- (n equals 7) from +1.7 +/- SE 0.5 TO +3.3 +/- SE 0.5 mueq/cm2 - h, and of Na+ (n equals 7) from -0.8 +/- SE 0.2 to +0.5 +/- SE 0.2 mueq/cm2 - h. Under open-circuit conditions, acetylcholine (5 X 10(-5) M) increased significantly the unidirectional flux of Cl- (n equals 6) toward the lumen from 4.7 +/- SE 1.3 to 5.9 +/- SE 1.4 mueq/cm2 - h, while the other measured fluxes did not change significantly, suggesting that net Cl- flux had increased toward the lumen. Atropine sulfate (10(-8) M) prevented the response to acetylcholine (5 X 10(-5) M). The increased ion flux due to acetylcholine may mediate water secretion into the airway lumen, and this secretion may have important effects on the physical properties of the liquid through which the respiratory cilia beat.

Changes in renal hemodynamics and renin release caused by increased plasma oncotic pressure

Hall, Guyton — 1976-11-01

The effect of increased plasma oncotic pressure on renal blood flow (RBF), glomerular filtration rate (GFR), electrolyte excretion, and renin secretion rate (RSR) was studied in dogs anesthetized with sodium pentobarbital. Renal artery infusions of hyperoncotic dextran or human serum albumin raised renal venous colloid osmotic pressure an average of 7.3 and 10.1 mmHg, respectively, and caused small but consistent increases in RBF, large increases in RSR, marked decreases in urine flow rate and electrolyte excretion, with either no change or small decreases in GFR, and no change in renal artery pressure. Renal vasodilation was confined primarily to afferent arterioles and was not measureable until approximately 45 s after the start of infusions. The renal responses to increased plasma oncotic pressure appeared to be an autoregulatory phenomenon, consistent with a tubular mechanism dependent on an altered distal tubular fluid flow and/or composition. The increased renin release during increased plasma oncotic pressure is not compatible with a renal baroreceptor mechanism that responds to decreases in afferent arteriolar pressure because calculated glomerular pressure increased during albumin and dextran infusions.

Ornithine decarboxylase in rat small intestine: stimulation with food or insulin

Maudsley, Leif, Kobayashi — 1976-11-01

Ornithine decarboxylase in the small intestine of starved rats was stimulated 3- to 10-fold by refeeding or administration of insulin. A peak is observed 3-5 h following treatment after which the enzyme activity rapidly declines. The rise in ornithine decarboxylase is reduced by actinomycin D or cycloheximide. The increase in enzyme activity occurs mainly in the duodenum and jejunum with less than a twofold change being observed in the ileum. A small (twofold) increase in S-adenosylmethionine decarboxylase activity in the small intestine was observed after food, but there was no change in diamine oxidase activity. Whereas pentagastrin and metiamide administration markedly stimulated histidine decarbosylase in the gastric mucosa, no consistent effect of these agents on ornithine decarboxylase in the small intestine was observed. The similarities and differences between histidine decarboxylase and ornithine decarboxylase are discussed.

Effects of ions on amylase release by dissociated pancreatic acinar cells

Williams, Cary, Moffat — 1976-11-01

Dissociated acinar cells prepared from guinea pig and mouse pancreas were intact on the basis of structure, ion content, and their ability to increase release of amylase in response to bethanechol and the calcium ionophore A23187. Guinea pig but not mouse acinar cells increased amylase release in response to caerulein. An increase in the concentration of K+ in the medium, which increases amylase release from whole pancreas, did not increase release. The effect of varying the ionic content of the medium on basal and stimulated amylase release was studied. Bethanechol and caerulein were still able to stimulate amylase release when Ca2+ was omitted from the medium, whereas stimulation induced by A23187 was abolished. Elevation of the concentration of Mg2+ did not affect basal or stimulated amylase release. Removal of Na+ from the medium initially had no effect on amylase release although bethanechol-stimulated release by mouse cells was inion of the HCO3- or Cl- content of the medium did not affect cholinergic stimulation of secretion. It is concluded that stimulated amylase release by isolated acinar cells is relatively independent of the ionic constituency of the bathing medium.

Water content of rat adipose tissue and isolated adipocytes in relation to cell size

DiGirolamo, Owens — 1976-11-01

Epididymal adipose tissue composition and adipocyte water content were studied in male rats during growth and development of spontaneous obesity. The data show that a highly significant positive correlation exists between fat-cell volume and intracellular water space (IWS) (r=.967, P less than .001). Intracellular water, expressed as picoliters per fat cell, varied from 1.5-2 in small fat cells (mean vol, 30-50 pl) to 9-10 in large cells (800-1,000 pl). When expressed as percent of fat-cell volume, IWS varied from 5-7% in the small fat cells to 1-1.3% in the large ones. Total adipose tissue water continued to increase with increasing adipose mass. Similarly, total adipocyte water increased with enlarging cell size and tissue mass. The contribution of total adipocyte water (as contrasted to that of nonadipocyte water) to total tissue water, however, was found to be limited (less than 23%) and to decline progressively with adipose mass expansion.

Midbrain neuronal responses to local and spinal cord temperatures

Hori, Harada — 1976-11-01

Water-perfused thermodes were implanted over the lumbothoracic spinal cord and unilaterally in the midbrain of urethan-anesthetized rabbits. Single-unit activities were recorded with steel microelectrodes from the thermosensitive neurons in the midbrain reticular formation (MRF), and the effects of heating and cooling of the spinal cord were studied. Of 38 cold-sensitive MRF neurons studied, 7 units decreased their firing rate upon elevation of spinal cord temperature (Tsc) and 3 units showed the opposite type of response to Tsc. The remaining 28 cold units were not affected by the changes in Tsc between 30 and 43 degrees C. Of 17 warm units, 3 units increased and one unit decreased the firing rate during spinal cord heating. These results suggest that the temperature signal arising from thermosensitive structures in the spinal cord may be transmitted to some of the locally thermosensitive neurons in the MRF.

Effects of angiotensin, vasopressin, and methoxamine on cardiac function and blood flow distribution in conscious dogs

Heyndrickx, Boettcher, Vatner — 1976-11-01

A comparison was made of the effects of vasopressin (ADH), methoxamine (MX), and angiotensin II (AN) on coronary and left ventricular dynamics, cardiac output, and regional blood flow distribution in intact, consci9us dogs. At an equal percent pressure elevation, ADH reduced cardiac output and cardiac rate the most, while AN had the least effect. After denervation of arterial baroreceptors, ADH still reduced heart rate, while AN increased it, suggesting nonbaroreceptor negative and positive chronotropic effects, respectively. A differential pattern on peak dP/dt was also observed, with ACH causing a greater reduction than MX while AN did not decrease dP/dt. With heart rate held constant, AN did not reduce dP/dt, suggesting a direct positive inotropic effect since dP/dt should have fallen slightly due to reflex mechanisms, as was observed with MX and ADH. ADH induced the greatest increase in coronary resistance (140%), while the least (46%) was observed with AN, which could be explained, in part, by the differential effects observed on cardiac rate and contractility. The greatest increase in resistance in the iliac bed occurred with ADH (30%), and the least with AN (34%). Conversely, the greatest constriction in the renal bed occurred with AN (95%), and lesser amounts were observed with ADH (36%) and MX (35%). Thus ADH, MX, and AN exert potent yet differential vasoconstricting actions on peripheral beds. In addition, while all three agents elicited coronary vasoconstriction, the differential effects on coronary vascular resistance appeared to be due predominantly to a difference in chronotropic and inotropic actions.

Absorption and exchange of water across rumen epithelium

Dobson, Sellers, Gatewood — 1976-11-01

The osmotic pressure of solutions in the ventral sac of the rumen of the conscious cow was varied with Na Cl or mannitol. The mucosal blood flow measured by HTO clearance was minimal when the lumen contained an isotonic solution and rose threefold when the rumen was hypo- or hypertonic to plasma by 150 mosmol/kg. Thus osmotic gradients actoss the rumen epithelium stimulated mucosal blood flow. Using osmotic gradients small enough to avoid blood flow stimulation, the net water flow could be enhanced by butyrate, a chemical stimulator of blood flow. Thus water movement was partially limited by blood flow. This implied an appreciable change in osmotic pressure of the capillary blood toward that of the rumen contents. The relative importance of blood flow, membrane permeability, and solute uptake on water transport was assessed. The osmotic pressure in the rumen was stationary when the rumen solution was distinctly hypotonic to plasma. The absorbate in the absence of an osmotic gradient was thus hypertonic. The net uptake of solute increased rapidly when the solution in the lumen was hypertonic to plasma. This gave rise to a more rapid rate of change of osmotic pressure in the rumen under this condition.

Dependence of Cr-EDTA absorption from the rumen on luminal osmotic pressure

Dobson, Sellers, Gatewood — 1976-11-01

A method for the measurement of [51Cr]EDTA absorption from the ventral sac of the rumen with an error of the order of +/-10% is described. When a solution present in the rumen was hypotonic or isotonic, the absorption rate of [51Cr]EDTA expressed as a clearance was about 0.2 ml/min. This gave rise to negligible errors when [51Cr]EDTA was used as an unabsorbed marker to calculate net water movements. When the osmotic pressure in the rumen exceeded that of plasma by 30-40 mos-mol/kg, the absorption rate of [51Cr]EDTA appeared to be related to the degree of hypertonicity. Absorption rates as high as 8 ml/min were observed within a range of osmotic pressures normally encountered postprandially in the rumen. Under hypertonic conditions, a correction for the absorption of this large anion was necessary if passage of water into the lumen were not to be systematically overestimated.

Basis for synchronization of sympathetic and phrenic nerve discharges

Barman, Gebber — 1976-11-01

The basis for the relationship between the discharges in the external cartized cats that were vagotomized, paralyzed, and artificially ventilated. Ive discharge (with the period of the cycle of phrenic nerve activity) is extrinsically imposed on central sympathetic networks by elements of the brainstem respiratory oscillator. However, a number of observations made in the present study contradict this view. First, changes in respiratory rate were accompanied by dramatic shifts in the phase relations between sympathetic and phrenic nerve discharge. Second, slow oscillations of sympathetic and phrenic nerve discharge were not always locked in a 1:1 relation. Third, the slow sympathetic rhythm persisted when respiratory rhythmicity disappeic components of sympathetic and phrenic nerve activity are generated by in

Simulation study of control of hepatic glycogen synthesis by glucose and insulin

El-Refai, Bergman — 1976-11-01

The plausibility of various hypotheses concerning the effects of glucow dynamic model of glucose metabolism in the liver. The model consisted of six compartments representing extracellular glucose, and intracellular glucose, glucose 6-phosphate, glucose 1-phosphate, uridine diphosphate glucose, obtained from literature reports, the model predicted values of intermediates which were close to those reported for the liver, sampled from fasting animals. The model predicts that glucose can generate significant glycogen deposition by engendering the inhibition of glucose-6-phosphatase, but not by mass action, glycogen synthase activation, or phosphorylase deactivation. The model predicts that, although insulin can inhibit glucose production by lowering phosphorylase and gluconeogenesis, only an insulin-mediated induction of glucokinase can account for insulin's action to potentiate the effect of glucose alone on glycogen synthesis.

PO2-modulated performance of cardiac muscle

Frezza, Bing — 1976-11-01

An inverse linear relationship between normalized tension development (T/mm2) and muscle cross-sectional area (range 0.32-1.68 mm2) is seen in fully oxygenated rat papillary and columnar carnease muscles studied while contracting isometrically at the apex of the length-tension curve. The data demonstrate progressively poorer performance with thicker preparations, presumatic blockade) is added to fully oxygenated muscle preparations, no significant change in performance is seen even with the thickest preparations, suggesting that no portion of mechanical activity is supported by anaerobic glycolysis. With progressive lowering of the muscle bath PO2, the relative contributions of aerobic and glycolytic activity to mechanical performance are demonstrated. Viewed from the Hill model of oxygen and lactic acid distribution in a cylindrical section of muscle, the data that suggest the presence of a hypoxic core appear contrary to the evidence that indicates the absence of tension supported by glycolytic activity. A possible solution to this apparent contradiction is presented. The findings of these experiments emphasize limitations of isolated muscle studies and help define the relationship between oxygenation and mechanical activity of cardiac muscle.

Compensatory phosphaturia after unilateral nephrectomy in the rat

Lehne, Coe — 1976-11-01

Within 24 hr after unilateral nephrectomy, fractional excretion of phosphate (FEp) by the remaining kidney is markedly increased. This increase in FEp occurs in throparathyroidectomized rats receiving fixed replacement doses of parathyroid hormone and, therefore, cannot be due to secondary hyperparathyroidism occurring in response to unilateral nephrectomy. In the avsence of any hormone replacement, the increase in FEp is much reduced, but still present. The increase in FEp cannot be ascribed to depression of overall tubular sodium reabsorption because it could be demonstrated in the absence of an increase in FENa. Phosphaturia following unilateral nephrectomy in the rat appears to be part of the complex of events that occur after acute reduction of renal mass; the exact mechanisms of its genesis are uncertain.