[Effect of nitroglycerin on the contractility of the myocardium under various supplies of oxygen].

Nitroglycerin was shown to induce significant positive inotropic effect in adequate oxygen supply in isolated papillary muscles of the rat heart left ventricle. The effect depended upon inotropic reserve of the myocardium. The decrease in oxygen supply of papillary muscles inhibited their contractile activity. In these conditions, nitroglycerin exerted no positive inotropic influence on papillary muscles. Positive inotropic action of nitroglycerin became weaker after preliminary perfusion of papillary muscles with propranolol. Calcium antagonist verapamil completely abolished the positive inotropic action of nitroglycerin. The data suggest that positive inotropic action of nitroglycerin depends upon transsarcolemmal influx of calcium ions and is partially associated with the stimulation of myocardiac beta-receptors.