In rats under ether anaesthesia, the left coronary artery was ligated and reperfused after 10 min of ischaemia. Forty-eight hours later the myocardium was analyzed for creatine kinase (CK) activity. 2. Human superoxide dismutase (h-SOD) given 1 min after occlusion and again 6 h later significantly improved survival and retarded the loss of myocardial CK. 3. In rat isolated hearts perfused at 15% of normal flow for 30 min followed by re-establishment of normal flow for 20 min, perfusion pressure increased by 72% and myocardial CK decreased by 44%. No significant changes occurred in wet-to-dry heart weight ratio. 4. Administration of h-SOD at 2.5 or 5.0 mg, significantly attenuated the elevated post-ischaemic perfusion pressure and the loss of myocardial CK activity in rat perfused hearts. 5. h-SOD appears to be an effective anti-ischaemic agent in the intact animal as well as the isolated perfused heart of the rat subjected to low flow followed by reperfusion at normal flow. The mechanism of this cardioprotective effect is not totally dependent upon the formed elements of the blood, but may be partially due to a direct cytoprotective effect.
