Role of Xanthine Oxidase in Reperfusion Injury In Ischemic Myocardium

Abstract

The present studies were conducted to confirm the hypothesis that xanthine oxidase- linked cytotoxic oxygen free radicals play an important role in producing the reperfusion injury of ischemic myocardium. The reperfusion injury was induced in isolated, Langendorff preparations of rat hearts by 60 min of global ischemia with aortic clamping followed by 20 min of reperfusion with oxygenated Krebs- Henseleit solution. Upon reperfusion of ischemic hearts, the release of creatine phosphokinase, lactic dehydrogenase and a lipid peroxidation product, malondialdehyde into the coronary effluent was abruptly increased. The increase of the enzymes and malondialdehyde was supprressed significantly in the presence of superoxide dismutase or catalse during the reperfusion period. In the hearts removed from rats pretreated with a specific xanthine oxidase inhibitor, allopurino1(20 mglkg, orally 24 hrs and 2 hrs before study}, the increased release of the enzymes and malondialdehyde was also significantly depressed. This effect of allopurinol was comparable to that of oxygen radical scavengers. When ferricytochrome C was infused to the hearts starting with reperfusion, the SOD-inhibitable reduction of ferricytochrome C increased during the first minute of reperfusion. Hydrogen peroxide measured in the coronary effluents also increased markedly with the similar time course as ferricytochrome C reduction. In the hearts treated with allopurinol, however, both the ferricytochrome C reduction and HzOz were not increased significantly. Myocardial content of xanthine oxidase was determined for D-form, O-form and D/O-form separately in the normal control hearts and the ischemic ones. Total enzyme content was similar in both hearts. Compared with the normal control, however, the ischemic hearts showed lower activities in D-form and D/O-form, and higher activity in the oxygen radical producing O-form. The proportion of O-form to the total enzyme was much higher in the ischemic heart than in the normal control heart. After 60 min of ischemia, myocardial content of total adenine nucleotides were reduced to 40% of the normal control value, while their catabolic products, hypoxanthine and xanthine were accumulated significantly. These. results provide evidence that xanthine oxidase is involved in the production of oxygen free radicals during the reperfusion of ischemic heart, and plays a contributing role in the genesis of reperfusion injury.