Endogenous nitric oxide modulates myocardial oxygen consumption in canine right ventricle

The role of endogenous nitric oxide (NO) in modulating myocardial oxygen consumption (MVO2) is unclear, in part because of systemic and coronary hemodynamic effects of blocking NO release. This study evaluated the effect of NO on right ventricular MVO2 under controlled hemodynamic conditions. In 12 open-chest dogs, N(omega)-nitro-L-arginine methyl ester (L-NAME, 150 microg/min), a NO synthase (NOS) blocker, was infused into the right coronary artery. Heart rate and mean aortic pressure were constant. Right coronary blood flow and right ventricular MVO2 were measured at normal and elevated right coronary perfusion pressures (RCP) before and after L-NAME. To avoid effects of NO synthesis blockade on right coronary blood flow, which might have altered right ventricular MVO2, experiments, were conducted during adenosine-induced maximal coronary vasodilation. L-NAME did not affect right coronary blood flow (P = 0.51). However, L-NAME significantly increased right ventricular MVO2 (6% at RCP 100 mmHg, and 21% at RCP 180 mmHg). Right coronary blood flow varied with perfusion pressure (P < 0.02), and the elevation of MVO2 produced by L-NAME increased at higher flows (P < 0.04), consistent with the greater shear stress-mediated release of NO. These findings indicate that endogenous NO limits right ventricular MVO2.