To investigate whether iron is involved in the reperfusion syndrome by aggravating free radical injury, the hearts from iron-loaded and control rats were perfused under normoxic, anoxic, and reperfusion conditions. Normoxic perfusion revealed no change in coronary flow, contractility, or lactate dehydrogenase (LDH) release between these two groups. Under anoxic and reperfusion conditions, however, we found a significant increase of ventricle fibrillation (56% vs. 0%, p

In this study, we investigated the role of oxygen-derived free radicals and iron in mediating myocardial injury during ischemia and reperfusion. Iron is of special interest because it may enhance tissue injury during ischemia and reperfusion by catalyzing the formation of highly reactive hydroxyl radicals (by modified Haber-Weiss or Fenton reactions). Rat hearts, perfused by the Langendorif method, were subjected to global ischemia (15 minutes at 370 C) and reperfusion. The effects of two iron chelators, 1,2-dimethyl-3-hydroxy-4-pyridone (L1) and 5-hydroxy-2-hydroxymethyl-4-pyrone (kojic acid), and one antioxidant, (+)-cyanidanol-3, on contractile function, coronary flow, lactate dehydrogenase release, and lactate production were studied. The combination of these iron chelators is of special importance because Li is known to prevent lipid peroxidation, induced by ADP/Fe3' and NADPH in microsomes, in contrast to kojic acid. We found significant protection of contractile function (apex displacement) during reperfusion with 50 kM Li and 20 ,uM (+)-cyanidanol-3 (p<0.01, n=6), whereas no protection was found with 50 ,uM kojic acid (n =6). Measurements of lactate dehydrogenase release during reperfusion showed a protective pattern similar to that found for heart contractile function, although 50 ,&M kojic acid also showed a significantly lower lactate dehydrogenase release during the first 10 minutes of reperfusion. No diferences in coronary resistance or lactate release were found between the various groups. Our findings indicate that iron and oxygenderived free radicals are important in the pathogenesis of postischemic reperfusion injury probably because of the formation of hydroxyl radicals. During heart ischemia, administration of the orally active iron chelator Li or the antioxidant (+)-cyanidanol-3 may be a promising approach in establishing postischemic cardiac protection. (Circulation 1989;80:158-164)

The present study was designed to measure directly, using e.p.r. spectroscopy, oxygen-derived free radicals in (post)-ischaemic or (post)-anoxic rat hearts. Rat hearts were rapidly freeze-clamped at 77 K under normoxic, anoxic, ischaemic or reperfusion conditions. The samples were measured at three different temperatures (13, 77 and 115 K) and at several microwave power levels, and were compared with isolated rat heart mitochondria. Samples were prepared both by grinding and as tissue cuts. The two preparation techniques gave identical e.p.r. results, which excludes the occurrence of grinding artifacts. No free radical signals linked to reperfusion injury were detected. Several electron transfer centres known in the mitochondrial respiratory chain were measured. The signals previously assigned to post-ischaemic reperfusion injury were found to originate from electron transfer centres of the respiratory chain, predominantly the iron-sulphur cluster S-1 in succinate dehydrogenase. The differences in signal intensity between normoxic, ischaemic and reperfused hearts were found to result from the different redox stages of these centres under the various conditions tested. These findings do not necessarily imply that oxygenderived free radicals are not formed in cardiac tissue during (post)-ischaemic reperfusion. The constitutive background of paramagnetism from the respiratory chain, however, seriously hampers the direct detection of comparatively low concentrations of free radicals in cardiac tissue. It is therefore expedient to focus future experiments in this field on the use of spin-trapping agents.

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