Several cyclooxygenase (COX) and lipoxygenase (LOX) products of arachidonic acid (AA) metabolism have been shown by our laboratory to produce a cardioprotective effect in the ischemicreperfused canine myocardium, examples being PGI2, PGE1 and 12-HETE. However, very little data exist concerning the cardiac effects of the products of the other major pathway of AA metabolism, the cytochrome P-450 (CYP) pathway. In a well-established model of canine myocardial infarction and in isolated rabbit cardiomyocytes, we hypothesize that the CYP metabolites of AA are released during ischemia and reperfusion and produce cardioprotection or enhance cardiac injury via the opening and/or blockade of ATP-sensitive (KATP) or calcium-activated potassium (Kca) channels in cardiac myocytes. Preliminary results indicate that during coronary artery occlusion and following reperfusion that increases in epoxyeicosatrienoic acids (EETs), dihydroxyeicosatrienoic acids (DHETs) and 20-hydroxyeicosatetraenoic acid (20-HETE) occur at the end of occlusion and throughout reperfusion and that by blocking their formation by two nonspecific CYP inhibitors, a marked reduction in myocardial infarct size occurred. In addition, we have preliminary data to suggest that exogenous administration of 20-HETE results in an increase in infarct size in the canine heart. Therefore, based on these intriguing results, we will study the role and cellular mechanisms by which the EETs, DHETs and 20-HETE modulate myocardial injury in an in vivo model of infarction and an in vitro model of hypoxia-reoxygenation. Specifically, we will identify and quantify the regioisomeric EETs, DHETs and 20-HETE that are produced by the heart as well as the CYP isoforms that are expressed in response to ischemia-reperfusion injury in dog hearts. Secondly, we will investigate the roles that CYP metabolites have on KATP channels and Kca channels in the ischemic-reperfused dog myocardium and on isolated adult rabbit cardiac myocytes exposed to hypoxia-reoxygenation and the major CYP pathways involved. Finally, we will investigate the interaction of the COX and/or LOX pathways with the CYP pathway during ischemia-reperfusion and hypoxia-reoxygenation. Our use of integrative physiology, pharmacology, chemistry and molecular biology in well-established cell and animal models is a powerful approach for identifying the role that the CYP pathway serves in ischemia-reperfusion injury.
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