1. In the lung and liver of tocopherol-deficient rats, the activities of glutathione peroxidase and glucose 6-phosphate dehydrogenase were increased substantially, suggesting an important role for both enzymes in protecting the organ against the deleterious effects of lipid peroxides. 2. Facilitation of the glutathione peroxidase reaction by infusing t-butyl hydroperoxide caused the oxidation of nicotinamide nucleotides and glutathione, resulting in a concomitant increase in the rate of release of oxidized glutathione into the perfusate. Thus the rate of production of lipid peroxide and H2O2 in the perfused organ could be compared by simultaneous measurement of the rate of glutathione release and the turnover number of the catalase reaction. 3. On hyperbaric oxygenation at 4 × 10(5)Pa, H2O2 production, estimated from the turnover of the catalase reaction, was increased slightly in the liver, and glutathione release was increased slightly, in both lung and liver. 4. Tocopherol deficiency caused a marked increase in lipid-peroxide formation as indicated by a corresponding increase in glutathione release under hyperbaric oxygenation, with a further enhancement when the tocopherol-deficient rats were also starved. 5. The study demonstrates that the primary response to hyperbaric oxygenation is an elevation of the rate of lipid peroxidation rather than of the rate of formation of H2O2 or superoxide.

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