Reperfusion-induced arrhythmias: a study of the role of xanthine oxidase-derived free radicals in the rat heart.

We have assessed whether oxygen-derived free radicals produced by xanthine oxidase may be an important trigger mechanism in the genesis of reperfusion-induced arrhythmias. We have examined (i) the effects of inhibition of xanthine oxidase by both folic acid solution and amflutizole; (ii) the effects of the inhibitor of xanthine dehydrogenase to xanthine oxidase conversion, soybean trypsin inhibitor; (iii) the effects of administration of superoxide dismutase and catalase, both singly and in combination and (iv) in an isolated rat heart preparation we have investigated the ability of free radical scavengers to reduce reperfusion arrhythmias caused by the infusion of xanthine oxidase and hypoxanthine. The prior administration of folic acid solution, amflutizole, superoxide dismutase, catalase, and superoxide dismutase plus catalase all reduced the incidence of reperfusion-induced arrhythmias and resultant mortality, caused by reperfusion after a transient period of coronary artery occlusion in the anaesthetised rat. Prior administration of soybean trypsin inhibitor significantly reduced mortality. In an isolated, perfused rat heart preparation with temporary coronary artery occlusion, addition of xanthine oxidase-hypoxanthine to the perfusion medium increased the incidence of reperfusion arrhythmias and decreased the total duration of sinus rhythm during reperfusion. Further addition of superoxide dismutase or L-methionine increased significantly the total duration of sinus rhythm. These results suggest that in the rat heart xanthine oxidase may be involved in the genesis of reperfusion-induced arrhythmias.