Nitric oxide signaling in ischemic heart

Objective: Several recent studies have implicated a role of endogenous nitric oxide (NO) in the pathophysiology of myocardial ischemic/reperfusion i jury. However, the mechanism by which NO exerts its beneficial/detrimental effects remains unknown. This study examined the intracellular signaling of NO by studying the role of the NO-cGMP signaling pathway on the phospho-diesteratic breakdown and turnover of phosphoinositides during myocardial ischemia and reperfusion. Methods: Isolated working rat hearts were made ischemic for 30 min followed by 30 min of reperfusion. A separate group of hearts were pre-perfused with 3 mM L-arginine for 10 min prior to ischemia. The release of NO was monitored using an on-line amperometric sensor. The aortic flow and developed pressure were examined to determine the effects of L-arginine on ischemic/reperfusion mjury. For signal transduction experiments, arcolemmal membranes were radiolabeled by perfusing the isolated hearts with [ 3H] myoinositol and [ “C]arachidonic acid. Hearts were then perfused for 10 min in the presence or absence of t.,-arginine via the Langendorff mode. lschemia was induced for 30 min followed by 30 min of reperfusion. Experiments were terminated before L-arginine and after L-a&nine treatment, after ischemia, and during reperfusion. Biopsies were processed to determine the isotopic incorporation into various phosphoinositols as well as phosphatidic acid and diacylglycerol. cGMP was assayed by radioimmunoassay nd SOD content was determined by enzymatic analysis. Results: The release of NO was diminished following ischemia and reperfusion and was augmented by L-arginine. L-Arginine reduced ischemic/reperfusion injury as evidenced by the enhanced myocardial functional recovery. cGMP, which remained unaffected by ischemia nd reperfusion, wa