Effect of hypoxic exercise on atrial natriuretic factor and aldosterone regulation

To evaluate the possible physiologic role of atrial natriuretic factor (ANF) in the observed dissociation of aldosterone secretion from the renin-angiotensin system during hypoxic exercise, 12 untrained men, ages 18 to 24, were studied on two separate days for 30 min during hypoxic (16% O2) and normoxic (room air) exercise on a bicycle ergometer. Workloads were adjusted to produce individual heart rates that remained within 70 to 75% of their previously measured maximum. Hemoglobin saturation decreased during hypoxia from 98 +/- 0.1% to 90 +/- 0.4% (P less than .01). Plasma aldosterone levels increased significantly (P less than .01) under both breathing conditions, yet were on average 36% lower during hypoxia than during normoxia (P less than .001). Plasma ANF levels increased during exercise under both conditions (P less than .01), yet levels were 45% greater during hypoxia than during normoxia (P less than .001). Plasma renin activity, adrenocorticotropic hormone, cortisol, potassium, and systolic blood pressure increased during exercise on both study days (P less than .01, compared to basal level), and showed no difference between normoxic and hypoxic conditions. Plasma pH was slightly higher during hypoxic exercise (P less than .05, compared to normoxia). We conclude that acute hypoxemia is a potent enhancing stimulus for ANF release during dynamic exercise and that ANF is probably a contributing factor in the dissociation of aldosterone secretion from the renin-angiotensin system under these conditions.