Hypoxic, isolated rat heart: hemodynamic and metabolic effects of nitroglycerin

The purpose of the study was to evaluate the effects of nitroglycerin on the mechanical and metabolic performance of the mammalian heart without interference from peripheral vascular and neurohumoral influences. Isolated rat hearts were perfused with a buffer containing 1 mug of alcoholic nitroglycerin/ml or an equivalent amount of alcohol. Mechanical performance was analyzed during external and isovolumic work; all hearts were subjected to mild hypoxia. Heart rate was kept constant by pacing. At constant atrial filling pressures end diastolic pressures and calculated wall stiffness were not significantly different for controls and nitroglycerin. Afterload, as quantitated by mean aortic pressure, was the same for both groups. Peak-systolic left ventricular pressure and dp/dt max during ejection and isovolumic work were significantly reduced by hypoxia (p less than 0.001), but not changed by nitroglycerin. Cardiac output, mean systolic left ventricular pressure, work, oxygen consumption, and calculated efficiency were decreased by hypoxia (p less than 0.001); lactate production was enhanced by the hypoxic state (p less than 0.001). Nitroglycerin had no influence on these parameters in either state. It is concluded that at constant rate, preload and afterload nitroglycerin has no effect on the mechanical performance and energy formation by aerobic and anaerobic means in the fully oxygenated and mild hypoxic state.