Conditions associated with ischemia/reperfusion injury (IRI) such as myocardial infarction and acute ischemic renal failure are among the major causes of morbidity and mortality. The pathophysiology of IRI is strikingly similar in heart and kidney, with enhanced production of toxic metabolites (i.e. H202), increased apoptosis, and cell death following reperfusion, raising the possibility that identical pathway(s) may mediate cell injury and dysfunction in both organs in IRI. In an attempt to identify the factors involved in the pathophysiology of IRI, suppression subtractive hybridization on RNA from normal rat kidneys and kidneys of animals subjected to 30 min of ischemia (renal artery ligation) followed by 12 hrs of reperfusion was performed. The results identified enhanced expression of Spermidine/Spermine N-1 acetyltransferase (SSAT), the rate limiting enzyme involved in the catabolism of polyamines, in IRI. Interestingly, thirty (30) min of ischemia (left anterior descending artery ligation) followed by 6-12 hrs of reperfusion resulted in the induction of SSAT in the injury zone in myocardium, with SSAT expression being almost undetectable in normal myocardium and increasing by >50-fold at 6 hrs of reperfusion. Enhanced SSAT expression in kidney and heart in IRI was associated with increased concentrations of putrescine, a mediator of apoptosis and a phenomenon indicative of increased activity of SSAT. Conditional overexpression of SSAT in cultured cells resulted in decreased cell growth. The studies outlined in this proposal will test the hypothesis that SSAT is a biomarker of cell injury and its increased expression reflects the extent of tissue damage associated with IRI in heart and kidney. We further hypothesize that enhanced expression of SSA T in kidney or heart leads to cell damage through depletion of polyamines, production of toxic metabolites (e.g. H202, putrescine and various aldehydes) and induction of apoptosis. To test these hypotheses, we propose to: 1. Examine the expression and regulation of SSAT and polyamine pathway in renal and heart IRI, 2. Ascertain the role of SSAT over expression on cell survival and susceptibility to injury in renal and cardiac IRI, and 3. Ascertain the mechanism of SSAT-mediated cell injury in renal and cardiac IRI. Insight into the expression and regulation of SSAT and other enzymes involved in polyamine metabolism in IRI will shed new lights into the pathophysiology of IRI in heart and kidney and may provide basis for novel diagnostic tests and therapeutic options targeted at early detection, prevention or treatment of ischemic heart attack and acute ischemic renal failure.