Importance of oxygen free radicals during ischemia and reperfusion in the experimental and clinical setting. Oxygen free radicals and the heart.

In recent years there has been considerable interest concerning the role of oxygen radicals in myocardial ischemia and reperfusion injury. The sequential univalent reduction of oxygen gives rise to very reactive intermediate products. Normally, the tissue concentration of these intermediate products of oxygen is limited and the aerobic myocardium survives because of the existence of a delicate balance between the generation of the various oxidants and the maintenance of the antioxidant defense mechanism. Several possible sources have been identified for the production of active oxygen species after ischemia and reperfusion and these sources may be mutually interactive. The ability of scavengers of oxygen free radicals to improve mechanical, mitochondrial, and sarcoplasmic reticulum function in animal models of ischemic-reperfusion injury also suggests that oxygen free radicals are partly responsible for myocardial damage in these models, although caution in the interpretation of these data is necessary. Evidence in favour of and against this hypothesis is described in detail in the present article.