The regulation of aldosterone secretion in primary aldosteronism

Twenty patients with primary aldosteronism were studied under various conditions known to influence aldosterone secretion. All patients presented with the classic findings of hypertension, hypokalemia, suppressed plasma renin activity and nonsuppressible aldosterone secretion. At surgery all patients had adrenal adenomas, and hypertension disappeared or diminished in all but one case. Further study of these patients was performed to determine the factors controlling aldosterone secretion in this disease. Aldosterone responses to dietary alterations of sodium or potassium, saline infusion, dexamethasone suppression, volume depletion, ACTH stimulation both in vivo and in vitro, and angiotensin stimulation in vitro were evaluated. Aldosterone secretion was altered by all direct acting stimuli (ACTH, potassium and angiotensin II) but not by those working indirectly through volume expansion or depletion. Thus, these tumors were still responsive to regulatory factors despite suppression of the renin-angiotensin system. Although these patients had a normal diurnal rhythm of aldosterone indicative of an ACTH effect, the major determinants of the daily output were probably potassium and the size and biosynthetic capacity of the tumor. This altered regulatory mechanism has important diagnostic considerations since it means that dietary intake of both sodium and potassium and the hypokalemia induced by sodium loading may alter aldosterone secretion or plasma levels.