Prolonged Infusions of Ile5-Angiotensin-II in Sodium Replete and Deplete Man: Effects on Aldosterone, ACTH, Cortisol, Blood Pressure, and Electrolyte Balance*

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Abstract
Angiotensis II (Ile5) was infused for 72 h into 4 Na replete (3 ng/kg per min) and 8 Na deplete (3 or 6 ng/kg per min) healthy young men after appropriate control periods, and the effects on aldosterone secretion, plasma cortisol, ACTH, renin activity, plasma and urinary electrolytes and blood pressure were assessed. Sustained contrived elevation of plasma angiotensin II levels in Na replete subjects to the range of moderate Na depletion led to a sustained increase in plasma and urinary aldosterone levels, which further and significantly increased between the 1st and 2nd days of angiotensin II infusion, when gross Na retention during infusion was prevented. This additional increase may be explained as the expression of a trophic effect of angiotensin II on the zona glomerulosa. In the Na deplete state, the absolute increment of aldosterone secretion for a given elevation of angiotensin II levels during infusion was larger than in Na replete subjects. This confirms the conclusions from previous short-term angiotensin II infusion experiments that Na deficiency sensitizes the zona glomerulosa against angiotensin II. The trophic effect of angiotensin II on the adrenal gland seems to be mechanism by which the sensitization is brought about, but insufficient for its full explanation. Since plasma ACTH and cortisol, plasma Na and K concentrations, and K balance did not change significantly across Na depletion or angiotensin II infusion, the mechanism of sensitization awaits its full elucidation. The effect of angiotensin II on blood pressure was blunted by Na depletion. The opposite shifts in sensitivity against angiotensin II of the zona glomerulosa and of resistance blood vessels with changes in the Na state seem to be an effective and important means in the regulation of body Na.