CONSIDERATION of various isolated reports in the literature has led us to the hypothesis that oxygen poisoning and radiation injury have at least one common basis of action, possibly through the formation of oxidizing free radicals. This article reviews the pertinent material that led to this hypothesis and also presents the supporting evidence obtained from (i) experiments on the protective action against oxygen poisoning by substances of varied chemical nature known to increase resistance to irradiation, and (ii) experiments on the survival in oxygen of mice irradiated and exposed to high oxygen tensions simultaneously or at different intervals. Concerning free-radical formation, it is generally believed that the chemical actions of ionizing radiation on aqueous solutions are mainly indirect (1), involving the primary formation of the free radicals H' and OH" with subsequent formation of H202, atomic oxygen, and HO2' (2). In the presence of oxygen, increased amounts of the powerful and quantitatively important OH', as well as the less reactive but more persistent HG2', would be expected. Free-radical formation is also expected in normal oxidative metabolism. One mechanism by which molecular oxygen can be reduced is the compulsory univalent transfer of electrons described by Michaelis (3), according to which, in the presence of protons, one may expect the formation of OH', HO2', and H202. Daniels, et al. (4) have discussed the possible occurrence of an oxidizing free radical RO2' during the reduction of oxygen, and several other authors (5-10) have indicated the occurrence of free radicals 1 Based on work performed largely under Contract AF18-(600)556 with the
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