Changes in plasma phosphate with the stimulation of anaerobic metabolism in rats during hypoxic-anoxic states.

Exposure of rats to high altitude hypoxia causes a rapid decrease in plasma Pi: this change reached the maximum value after exposure to an altitude of 6000-7000 m. Lactate increased markedly when rats were exposed to a high altitude, above 5500-6000 m, although no increase in lactate was observed on exposure to an altitude below 5500 m. Highly anoxic conditions including cyanide and carbon monoxide poisoning cause a marked increase in inorganic phosphate (Pi) and lactate in plasma. Pi entering the intracellular spaces can be utilized as the substrate of oxidative phosphorylation during exposure to an altitude below 5500-6000 m, and for glycolytic enhancement in rats exposed to an altitude above 6000 m. The increase in plasma Pi may be explained by the inhibition of mitochondrial oxidation and the degradation of high energy phosphate compounds under highly anoxic conditions.