Renin-aldosterone and angiotensin-converting enzyme during prolonged altitude exposure

The effect of 7 wk altitude exposure on plasma renin activity (PRA), plasma aldosterone concentration (PAC), and angiotensin-converting enzyme (ACE) activity was studied in 10 male subjects at 4,500 m. There was an initial increase in PRA and a reduction in PAC and ACE. The reduction in ACE was significantly greater in the four subjects who had frequently been exposed to extreme altitudes than in the other six subjects. These changes had returned to control values between 12 and 20 days. Exercise caused a marked elevation of PRA and PAC, but the PAC response to PRA was blunted compared with that at sea level. The ratio PAC/PRA at rest was reduced initially but returned to control values with a similar time course to that of ACE activity. The results are compatible with the hypothesis that ACE activity governs the adrenal response to PRA.