Alteration in oxyhemoglobin equilibrium (P-50) and myocardial oxygen consumption (MVO2) by nitroglycerin (GTN)

In the isolated supported dog heart preparation perfused at a constant coronary blood flow, heart rate and left ventricular systolic pressure were not changed significantly by a 3-minute intracoronary infusion of nitroglycerin (5 and 10 mug/min). Nitroglycerin produced a significant increase in coronary venous pO2 and coronary venous P-50. These effects were accompanied by a significant decrease in myocardial oxygen consumption (MVO2). An infusion of dipyridamole (25 and 50 mug/min) did not produce significant changes in coronary venous pO2, P-50 or MVO2. Both drugs produced equivalent decreases in coronary artery perfusion pressure which suggests that the increase in coronary venous P-50 or reduction in MVO2 observed with nitroglycerin is not related to coronary vasodilation. The increase in P-50 induced by nitroglycerin was not accompanied by an increase in total erythrocytic 2,3-diphosphoglycerate and was not observed in vitro. The increase in P-50 produced by nitroglycerin provides a potential reservoir of readily diffusible oxygen that may be utilized during periods of myocardial hypoxia.