Renin-angiotensin II-aldosterone and ACTH-cortisol control during acute hypoxemia and exercise in patients with chronic obstructive pulmonary disease

Abstract

Acute hypoxia has been reported to induce a decrease in aldosterone levels despite no change or increases in plasma renin activity and ACTH. Converting enzyme inhibition and/or mild hypokalemia have been suggested as possible mechanisms for this dissociation. We studied 15 patients with chronic obstructive pulmonary disease (COPD) who used continuous ambulatory O2 therapy (home O2). Group A (n = 10) had O2 discontinued for 30 min before exercise to induce hypoxemia; Group B (n = 5) had O2 continued for 30 min (time control). Discontinuation of home O2 in Group A resulted in a significant fall in Pao2 from 77 +/- 6 to 51 +/- 2 torr. Arterial CO2 tension decreased and the pHa increased slightly. Renin, angiotensin II, plasma potassium, and sodium did not change during hypoxemia, whereas ACTH increased significantly. Despite this, aldosterone decreased from 26 +/- 5 to 18 +/- 2 ng/dl. Group B (time control) did not exhibit significant changes in hormones over 30 min, indicating that the effects observed in Group A were specific to O2 discontinuation. Exercise in Group A induced significant increases in ACTH, potassium, and aldosterone. We conclude from these data that acute hypoxemia in patients with COPD results in a decrease in aldosterone not related to converting enzyme inhibition, ACTH, or plasma potassium.