Effect of adenosine on myocardial oxygen balance.

The present study was designed to determine the effect of adenosine on oxyhemoglobin equilibrium (P-50) and myocardial oxygen consumption (MVO2) in the isolated supported dog heart preparation perfused at a constant coronary blood flow. Heart rate was controlled at 150 beats/min. A-3-minute intracoronary infusion of adenosine (10, 50 and 100 mug/min) produced significant decreases in MVO2, whereas coronary venous P-50 did not change. Adenosine-5'-monophosphate (5'-AMP) infusion (70 and 140 mug/min) did not produce a significant change in MVO2. Both adenosine and 5'-AMP caused equivalent decreases in coronary artery perfusion pressure and peak left ventricular systolic pressure. Furthermore, adenosine (50 and 100 mug/min) produced a significant decrease in MVO2 of the isolated supported fibrillating heart. These results suggest that the reduction in MVO2 observed with adenosine is not related to coronary vasodilation or to a negative inotropic or chronotropic action. Theophylline (2.5 mg/kg) partially blocked the hemodynamic effects of adenosine while completely abolishing the decrease in MVO2. Neither inosine nor hypoxanthine (50 and 100 mug/min) changed MVO2, P-50 or myocardial hemodynamics. Thus, in addition to its proposed role in coronary blood flow regulation, adenosine appears to exert important effects on myocardial metabolism.