Effects of Hyperbaric Oxygenation Metabolism II. Oxidative Phosphorylation in Rat Brain, Liver and Kidney.

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Abstract
Summary 1 Respiration and oxidative phosphorylation (using succinate and alpha-ketoglutarate as substrates) and succinic dehydrogenase activities were determined in homogenates of the cerebral hemisphere, liver and kidney cortex from rats previously exposed to normal air, and to 100% O2 for 2 hours at 1 and 3 atmospheres and for 1.5 hours at 5 atmospheres. 2 Increased respiration with both substrates was observed with increased exposure pressure in liver and cerebral hemisphere homogenates while efficiency of oxidative phosphorylation was retained. 3 Kidney homogenates showed decreased respiration with both substrates with normal efficiency for oxidative phosphorylation at all elevated oxygen pressure exposures. 4 Succinic dehydrogenase activity decreased in all 3 tissues with increasing pressure of O2 exposure. 5 Succinic dehydrogenase concentration is in excess of the amount required to maintain maximum respiration in all 3 tissues with succinate as the substrate. 6 Any inhibition of respiration and oxidative phosphorylation of succinate and alpha ketoglutarate in the cerebral hemisphere, liver and kidney cortex by hyperbaric oxygen exposures of rats, is reversible on returning tissues to normal oxygen tension. 7 There is no correlation between previously observed depressions in rat cerebral hemisphere, liver and kidney cortex ATP concentration with hyperbaric oxygen(1), and irreversible changes in respiration and oxidative phosphorylation of succinate and alpha-ketoglutarate. 8 There appears to be a correlation between the depression of ATP concentration of the cerebral hemisphere liver and kidney and the reduction in succinic dehydrogenase activity at exposure levels (5 atmospheres O2, 1.5 hours) which produce acute symptoms of oxygen toxicity in the rat. No such correlation is seen at 1 and 3 atmospheres O2 exposure for 2 hours.