It is well established that exposure of experimental animals to a hundred percent oxygen for longer than 24 hours results in adverse alterations of lung structure and function. It has been proposed that the observed cytotoxicity of alveolar epithelium and capillary endothelium result from oxygen free radical interactions with cell membranes and key enzyme proteins involved in the maintenance of ATP and the antioxidant reduced glutathione. Although in vitro studies with homogenates and subcellular fractions have suggested that the sulphydryl containing dehydrogenases of glyceraldehyde-3-phosphate, pyruvate, and glucose-6-phosphate are particularly sensitive to oxygen inactivation, few studies have examined whether such inactivations occur in the intact organ. It is the purpose of this study to use an isolated perfused rat lung preparation to assess those changes in metabolic function that occur prior to observable alterations in pathology and physiological function, resulting from 100% oxygen exposures. The specific hypothesis states that oxygen inactivates key metabolic enzymes involved in lung intermediary metabolism, and such inhibitions are initially reversible on cessation of exposure. Intracellular sites of oxygen interaction will be identified by in vitro measurements of glycolytic, pentose cycle and mitochondrial pathway fluxes in isolated perfused lungs isolated from normal and vitamin E deficient rats during the first 48 hours of in vivo exposure to 100% oxygen. Since perfusions with uncouplers and electron acceptors enhance tissue ATP and NADPH utilizations respectively, they will be used to define maximal metabolic fluxes. Such an approach, by providing an estimate of reserve capacity, represents a more sensitive method to examine early metabolic impairments, than has previously been possible with other in vitro systems. To establish whether glutathione is involved in preventing oxygen inactivation of lung sulphydryl 1 enzymes, lungs will also be perfused under conditions of limited glutathione supply, brought about by perfusion with t-butylhydroperoxide. Metabolic changes will be evaluated in lungs at different times after cessation of exposure in order to establish reversibility. These studies, therefore, provide a better understanding of the mechanisms of oxygen interaction, needed for future early detection and prevention of oxidant lung injuries.