Aldosterone response to sodium deprivation and angiotensin II in patients with hypopituitarism

Unknown pituitary factor(s) apart from ACTH may participate in the regulation of aldosterone (aldo) secretion in man. We investigated whether the 'sensitization' of the zona glomerulosa against angiotensin II (A II) by sodium deficiency was mediated by the pituitary gland. A II was infused in stepwise increasing doses (2, 4, 8 ng/kg/min) into 5 normal subjects (N) and into 8 patients with hypopituitarism (H) before and after 4 days on low sodium diet. Mean cumulative sodium balance after the low sodium diet was -145mM in N and -165mM in H. Plasma-aldo and aldo-excretion rate on the normal sodium diet were slightly higher in H than in N but rose less than normal during sodium depletion in H. Plasma A II and renin activity on normal sodium were slightly higher in H than in N, but the increase on the low sodium diet was blunted in H. The stimulation of plasma-aldo by A II infusion was similar in both groups on the normal sodium diet. In both groups, the response of P-aldo to A II infusion was greater in the sodium deplete than in the replete state, although 'sensitization' was slightly less marked in H than in N. This may be due to the blunted rise of plasma-A II after sodium loss in H, which may also account for abnormalities in the blood pressure response in the H group. Altogether, the results speak against a direct involvement of the pituitary gland in 'sensitization', but an indirect influence through unexplained abnormalities in renin secretion is possible.