In open-chest dogs anesthized with sodium pentobarbital, acetylcholine (ACh, 5 times 10'-5M) infused into the left circumflex coronary artery caused an increase in coronary flow and a decrease in myocardial O'2 extraction ratio (P less than .01) anduptake (P less than .05). Heart rate and mean arterial pressure were not altered,although left ventricular dP/dt declined from 2,037 plus or minus 205 to 1,873 plus or minus 194 mmHg/s (P less than .02). Intracoronary administration of norepinephrine (NE, 2.4 times 10'-6M) caused an increase in myocardial O'2 uptake (P less than .02); simultaneous infusion of both NE and ACh caused a decline in O'2 extraction ratio (P less than .01) and uptake (P less than 0.5). Myocardial adenylatecyclase activity in response to ACh was not altered significantly from a control levelof 188 plus or minus 22 pmol of '14C-labeled cyclic AMP/mg protein per 10 min. Norepinephrine alone elevated adenylate cyclase activity to 401 plus or minus 45 pmol ['14C]cyclic AMP/mg protein per 10 min (P less than .01). However, with simultaneous infusion of both NE and ACh, adenylate cyclase returned to control levels. Although ACh alone did not alter myocardial hormone-sensitive lipaseactivity, NE elevated lipolytic activity from 8.1 plus or minus .7 to 13.2 plus or minus 1.8 mueq free fatty acid (FTA)/g per 30 min (P less than .05). The administration of both ACh and NE returned lipase activity to nearly control levels. Myocardial uptake of FFA increased significantly during ACh infusion alone (P less than 0.5) and during NE infusion alone (P less than 905). However, when NE and AChwere administered together, a decline in FFA uptake was observed (P less than .02).These data indicate that the effects of ACh on cardiac metabolism are minimal, withthe decline in myocardial O'2 uptake of ACh primarily reflecting the decrease in contractility. On the other hand, antagonism of ACh on NE-stimulated myocardial lipid metabolism appears to involve activity of the adenylate cyclase system.
- Copyright © 1975 by American Physiological Society