Human Red Cell Metabolism and in Vivo Oxygen Affinity of Red Cells during 24 Hours' Exposure to Simulated High Altitude (4500 m)

Abstract

During exposure to high altitude the red cell metabolism was stimulated. An increase in the phosphofructokinase reaction occurred secondary to the elevated blood pH. An increase in the triosephosphate pool occurred secondary to PFK stimulation and a relative inhibition of the GAPDH reaction, which was due to the decrease in the concentration of inorganic phosphate. The low inorganic phosphate levels in both red cells and plasma were a consequence of a shift of phosphate from the extracellular fluid to other body cells during hyperventilation. The forward reaction of GAPDH was stimulated when the exposure to high altitude was accompanied by a moderate degree of physical exercise. This was indicated by the significant increase in red cell levels of 2,3-DPG, and 3PG and 2PG. This stimulation of the GAPDH reaction was probably due to an increased availability of NAD⁺, brought about by the influx of pyruvate from the muscles. The changes in the red cell metabolism influenced their oxygen affinity through changes in the level of 2,3-DPG. The accumulation of 2,3-DPG during the first 24 hours of exposure was found to reverse the CO₂-induced increase in oxygen affinity.