Pyridine nucleotide oxidases and transhydrogenase in acclimatization to high altitude

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Abstract
Activities of pyridine nucleotide oxidases and transhydrogenase have been examined in heart, liver and rectus femoris muscle of guinea pigs native to sea level and high altitude. There was found an enhanced reduced form of diphosphopyridine nucleotide oxidase (DPNH-oxidase) and transhydrogenase activity in heart and muscle from animals adapted to high altitude. In muscle the higher activity at altitude was due solely to increase in ratio of red to white portions. Both groups showed the pigmented portion twice as active as the white one. In liver, neither the DPNH-oxidase system nor the transhydrogenase were significantly changed in their activities on a fresh weight basis. Nevertheless, the DPNH-oxidase is higher at altitude when the activity is expressed per gram of nitrogen. The reduced form of triphosphopyridine nucleotide oxidase activity was not appreciably changed in any of the studied tissues. It was concluded that adaptation to high altitude is associated with apparent changes in the magnitude of the electron transport pathway. Increased activity in skeletal muscle is probably related to the tissue pigment content.