Plasma aldosterone and corticosterone responses to adrenocorticotropin, angiotensin, potassium, and stress in spontaneously hypertensive rats.

The responses of plasma aldosterone and corticosterone to ACTH, angiotensin II (AII), and potassium chloride (KCl) infusion and the aldosterone, corticosterone and PRA responses to immobilization stress were studied in 2-month-old spontaneously hypertensive rats (SHR) and age-matched Wistar-Kyoto (WKY) normotensive controls. Basal levels of plasma aldosterone and corticosterone were greater and PRA was less in the SHR than in the WKY. Aldosterone and corticosterone responses to graded AII were similar in both groups. Aldosterone and corticosterone responses to graded doses of KCl and ACTH, however, were significantly greater in SHR than in WKY normotensive rats. Plasma corticosterone, PRA, and aldosterone responses to immobilization stress were reduced in SHR compared to WKY. At 2 months of age, blood pressure was definitely elevated in SHR and was associated with low PRA and relatively high basal levels of aldosterone and corticosterone. Discordance between the renin-angiotensin system and mineralocorticoid secretion in the SHR may be due to enhanced adrenal sensitivity to factors such as ACTH and potassium. Suppressed PRA in SHR may be due, in part, to increased mineralocorticoid secretion, resulting in sodium retention and intravascular volume expansion.