Shift of anaerobic to aerobic metabolism in the rats acclimatized to hypoxia.

1. Metabolic acclimatization by repeated exposure to a simulated altitude of 4000, 5000 and 6000 m for 2 hr per day throughout 2 to 11 days was evaluated by the increased formation of ketone bodies as a marker of fatty acid oxidation and the decreased production of lactate and uric acid, the indicators of anaerobic metabolism in rats exposed to an altitude of 8000 m. 2. Pre-exposure of rats to an altitude of 5000 m and over caused an acclimatization to hypoxia. The rise of the altitude to which rats were pre-exposed reduced the period until the acquisition of metabolic acclimatization. 3. Acclimatized rats showed an increased activity of mitochondrial glutamate dehydrogenase without changes in glycolytic enzyme activity in skeletal muscle, heart and liver. 4. Acclimatization to high altitude hypoxia is concluded to involve a shift of the anaerobic glycolysis to aerobic metabolism by the increase in the oxidative enzymes.