The present study examined the effect of
hypoxia-induced
respiratory alkalosis on exercise-induced
metabolic acidosis and increases in plasma
lactate and
ammonia levels. Six male subjects underwent exercise of increasing intensity until exhaustion: (1) in normoxia (20.9% O(2)) (=MAX), (2) in
hypoxia (12% O(2)) (=HP) in which hypoxic condition had been maintained from 60 min before to 30 min after exercise, and (3) the same intensity of exercise as HP in normoxia (=SUB). Arterialized blood was drawn from a superficial vein. Post-exercise blood pH was significantly higher in HP than in MAX ( P<0.05), although plasma
lactate was at the same level. For
hypoxia as compared to normoxia, regression analysis confirmed a parallel shift of plasma
lactate to higher pH levels indicating the effect of
respiratory alkalosis ( P<0.01). After exercise plasma levels of
ammonia were lower in HP than in MAX ( P<0.05). Regression analysis between
ammonia and pH revealed nearly identical changes in
hypoxia and normoxia at low pH. From these results, we conclude that: (1)
hypoxia-induced
respiratory alkalosis attenuated exhaustive exercise-induced
metabolic acidosis, (2) plasma
lactate concentration was determined by the relative exercise intensity, (3) the maximum plasma
ammonia concentration under exhaustive exercise was reduced at
hypoxia because of
respiratory alkalosis.