The current proposal is aimed at investigating the role of the nuclear enzyme poly (ADP-ribose) synthetase (PARS) in the pathophysiology of myocardial ischemia-reperfusion injury. First, it will be established whether pharmacological inhibition of PARS ameliorates the cellular energetic derangement and the functional alterations during myocardial ischemia-reperfusion injury. This hypothesis will be tested in in vitro perfused heart preparations and in a mouse model of myocardial ischemia-reperfusion injury by correlating DNA strand-breakage, PARS activity, intracellular energetics, and myocardial contractility. PARS will be inhibited by pharmacological and molecular biological approaches. For the pharmacological approach, 3-aminobenzamide, a prototypical inhibitor of PARS will be used. Moreover, responses will be compared in hearts of wild-type mice and of knock-out mice lacking the functional PARS enzyme. The relative contribution of hydroxyl radical versus peroxynitrite in the activation of PARS in myocardial ischemia-reperfusion will also be addressed using pharmacological inhibitors. The principal investigator will also investigate the changes in endothelial function during myocardial reperfusion injury, and the role of PARS in these changes.