Renin, aldosterone, and vasopressin responses to hypoxia during 6 hours of mild exercise.

The effect of hypoxia (H) on plasma renin (PRA), aldosterone (PA), and arginine vasopressin levels (AVP) was evaluated during 6 h of mild exercise (treadmill: 0 grade, 1 mph). A crossover study was performed on seven male volunteers during steady state conditions of H2O, Na+ and K+ balance while breathing 12.5% O2 (PaO2 42 +/- 3 mm Hg) and room air (N, 21% O2). After exercise there were no significant differences in body weight, hematocrit, calculated plasma volumes, serum or urine osmolality, urine Na+ or K+ excretion or AVP. Mean arterial pressure (MAP) while exercising was reduced during hypoxia (86 +/- 2 vs. 92 +/- 4 mm Hg), p less than 0.05. Normal diurnal variation in serum cortisol was lost during exercise (N and H). Plasma renin and aldosterone levels fell with exercise in both groups: PRA N 3.3 to 2.4 vs. H 4.9 to 2.3 ng X ml-1 X h-1; PA N 6.5 to 2.8 vs. H 9.3 to 2.3 ng X dl-1 (p less than 0.05). Hypoxia per se did not exert influence beyond mild exercise regarding serum osmolality, urine osmolality or Na+ or K+ excretion. Sustained hypoxia during 6 h of mild exercise despite a lower MAP failed to elevate PRA, aldosterone, or AVP levels when normal hydration is maintained.