Renin, angiotensin-converting enzyme, and aldosterone in humans on Mount Everest

Plasma renin activity (PRA), serum angiotensin-converting enzyme (ACE) activity, and plasma aldosterone concentration (PAC) were measured in 15 subjects at sea level and at high altitude. Previous work has shown that on first ascent to altitude PAC and ACE are reduced, whereas PRA may be raised or reduced. After 2-4 wk at 6,300 m all hormones had returned to within +/- 10% of sea-level values. In seven subjects PRA and PAC were measured when exercise stopped. PRA and PAC were both elevated, PRA more than PAC; i.e., the PAC response to PRA was markedly blunted. Since ACE activity was normal, it is suggested that there may be down regulation, i.e., reduction in density of angiotensin II receptors on the adrenal cortex and/or induction of enzymes which degrade angiotensin II. This mechanism apparently protects the subjects from very high levels of PAC and sodium retention when hypoxia and exercise raise PRA to very high levels.