Effects of SOD, catalase, and a novel antiarrhythmic drug, EGB 761, on reperfusion-induced arrhythmias in isolated rat hearts.

Effects of superoxide dismutase (SOD), catalase, EGB 761 (Tanakan), and their combination on reperfusion-induced ventricular fibrillation (VF), tachycardia (VT), and the formation of oxygen free radicals were studied after 30 min of global ischemia followed by reperfusion in isolated rat hearts. In the first series of studies, rats received a daily dose of 10(4), 2 x 10(4), or 5 x 10(4) U/kg of SOD (i.v.); 2.5 x 10(4), 5 x 10(4), or 10(5) U/kg of catalase (i.v.); and 25, 50, 100, or 200 mg/kg of EGB 761 (per os), respectively, for 10 d (chronic administration). Neither SOD nor catalase alone reduced the incidence of reperfusion arrhythmias, but EGB 761 dose-dependently reduced the incidence of such arrhythmias. The coadministration of SOD (5 x 10(4) U/kg) with catalase (5 x 10(4) U/kg) significantly reduced the incidence of VF and VT. The same reduction in the incidence of VF and VT was observed when SOD (5 x 10(4) U/kg) was given in combination with EGB 761 (50 mg/kg). In the second series of studies, hearts were isolated and perfused with 5 x 10(4) U/l of SOD plus 5 x 10(4) U/l of catalase (acute treatment), and the incidence of reperfusion-induced VF and VT was significantly reduced. The combination of SOD (5 x 10(4) U/l) with EGB 761 (50 mg/l) also reduced the incidence of VF and VT. In these experiments, we studied the time course of oxygen radical formation using 5,5-dimethyl-pyrroline-N-oxide (DMPO), a spin trap, and it was found that EGB 761 (200 mg/l) or the coadministration of EGB 761 (50 mg/l) with SOD (5 x 10(4) U/l) almost completely abolished the formation of oxygen radicals during reperfusion measured by electron spin resonance (ESR) spectroscopy. Although SOD or catalase alone significantly reduced the formation of oxygen radicals, these drugs failed to prevent the development of reperfusion arrhythmias, while their combination significantly attenuated both the formation of free radicals and the incidence of reperfusion-induced arrhythmias. Our results indicate that the combination therapy may synergistically reduce the formation of free radicals and the incidence of reperfusion-induced VF and VT.