Aldosterone regulation in essential hypertension: altered adrenal responsiveness to angiotensin II

Adrenal responsiveness to angiotensin II was evaluated in patients with "normal-renin" hypertension. Plasma aldosterone, plasma renin activity, and angiotensin II levels were determined, in the supine and, after 21/2 hours in the upright position, in 70 patients with essential hypertension who were on a diet containing 10 meq of sodium and 100 meq of potassium. The increment of plasma aldosterone between supine and upright positions, divided by the increment in plasma renin activity (deltaPA/deltaPRA), was used as an estimate of adrenal sensitivity to angiotensin II. Fifty-seven patients had deltaPa/deltaPRA ratios within the range observed for a normotensive control population; 13 had low ratios. The low ratios suggested subnormal aldosterone responsiveness to angiotensin II. To further test this hypothesis, angiotensin II was infused into 19 of the 70 patients. In those patients with normal deltaPA/deltaPRA ratios, the plasma aldosterone response was similar to that observed in normotensive controls. On the other hand, in those patients with low ratios, a significant increase in plasma aldosterone levels did not occur even with a dose of angiotensin II 10 times higher than that producing an increase in the normally responsive group. In a separate study, the adrenal response to infused angiotensin II was determined in 12 hypertensive patients who were on a sodium intake of 200 meq. These patients were previously known to have normal renin levels after sodium restriction and upright posture. Under these conditions, the hypertensive patients as a group had a significantly greater plasma aldosterone increment to infused angiotensin II than did sodium-loaded normotensive control subjects. Thus, some patients with normal-renin essential hypertension may have either enhanced or reduced adrenal responsiveness to angiotensin II, depending on the conditions of dietary intake of sodium.