Aldosterone responses to ACTH during hypoxia in conscious rats

This study examined the aldosterone response to physiological ACTH infusion (4 ng/kg per min) and pharmacological ACTH injection (1.8 microgram) in conscious Long-Evans rats at 42 h of normoxia (21% O2) or hypoxia (10% O2). Hypoxia per se (no exogenous ACTH) significantly decreased control aldosterone levels despite elevated endogenous plasma ACTH). Hypoxia attenuated the aldosterone responses to ACTH infusion but not to ACTH injection. It was concluded that hypoxia attenuates aldosterone responses to small increases in ACTH, and large increases in ACTH can override this apparent decrease in adrenocortical sensitivity.