SIGNIFICANT LEVELS OF OXIDANTS ARE GENERATED BY ISOLATED CARDIOMYOCYTES DURING ISCHEMIA PRIOR TO REPERFUSION

Oxidants such as reactive oxygen species (ROS) have been shown to part icipate in myocardial ischemia/reperfusion injury. While many studies report a burst of ROS at reperfusion, few reports have presented evide nce of significant ROS generation during ischemia. Our previous studie s of cultured cardiomyocytes indicated that antioxidants are most effe ctive when given prior to reperfusion during ischemia. Therefore, we h ypothesized that significant ROS generation may occur during ischemia prior to reperfusion. We tested this in a perfused isolated cardiomyoc yte system (i.e. without neutrophils, endothelial cells, or xanthine/x anthine oxidase) during simulated ischemia/reperfusion while measuring oxidant generation using intracellular fluorescent probes. During isc hemia, the ROS probes dihydroethidium and 2', 7'-dichlorofluorescin we re significantly oxidized, suggesting superoxide and H2O2 generation. At reperfusion following Ih ischemia, these probes suggested a further burst of H2O2 and hydroxyl radicals. The antioxidants 2-mercaptopropi onyl glycine and 1,10-phenanthroline used during ischemia attenuated o xidant generation, increased cell viability, and improved return of co ntraction after ischemia. To further evaluate the relationship between residual O-2 and ROS generation, we administered O-2 scavengers durin g ischemia and measured corresponding changes in oxidant generation, c ell viability and contraction during reperfusion. Enzymatic scavenging of residual O-2 during ischemia (reducing PO2 from 3.5 to 2.5 tau) pa radoxically improved subsequent viability and contraction, These resul ts indicate that cultured cardiomyocytes generate significant ROS duri ng ischemia. This ROS generation is related to residual O-2 present du ring ischemia and contributes significantly to the cellular injury see n at reperfusion. (C) 1997 Academic Press Limited.