Characteristics of Acidic Urine After Loading With Weak Organic Acids in Dogs

Current Concepts on Renal Mechanisms of Acidification in Relation to Data on CO₂ Tension

¹ From the Department of Physiology and the Institute for Medical Research, University of Louisville School of Medicine, and the Department of Chemistry, Graduate School, University of Louisville, Louisville, Kentucky

Hydropenic, anesthetized dogs were given loading infusions of 0.5 m lactic acid and beta-hydroxybutyric acid with and without mannitol. In some experiments blood was collected from the femoral artery, and urine from the bladder. In other experiments, blood was collected from the renal vein, and urine from the renal pelvis. In serum, pH and CO₂ content fell to values as low as 6.7 and 4 mm/l., respectively. Urine flow reached maximal levels of 1.5–2.5 cc/min. after lactic acid alone, and 4.0–6.0 cc/min. after mannitol plus lactic acid. The pattern of osmotic activity versus urine flow was characteristic of a nonspecific type of osmotic diuresis. Titratable acid excretion increased to levels of 9–72 µm/min. Loading solute contributed to the bulk of the observed titratable acid even though its pKa was 1–2 u below the usual urinary pH. In urine, pH and CO₂ content were reduced to levels of 4.76 and 0.64 mm/l., respectively. Calculated value of CO₂ tension of urine was greater than that of plasma in 106 observations; was less than that of plasma in 33 observations; and was equal to that of plasma in 25 observations. Tonometric measurements were made on standard solutions and on samples of urine and plasma of two dogs during lactic acid acidosis. Tonometrically determined values of pCO₂ agreed (to within 1 mm of Hg) with calculated values of pCO₂.

Note:
with the technical assistance of Robert Greathouse and Thomas I. Moxley