Plasma aldosterone-renin interrelationships in various forms of essential hypertension: Studies using a rapid assay of plasma aldosterone

Abstract

Plasma aldosterone measurements using a new radioimmunoassay technique were included in a component analysis of the renin-aldosterone-sodium system. The studies involved 27 normal subjects and 51 patients with essential hypertension characterized by low, normal or high plasma renin activity. Noon plasma aldosterone concentrations closely reflected the state of aldosterone secretion. Thus, in normal subjects, plasma aldosterone values exhibited a relationship to the daily urinary sodium excretion similar to that for urinary aldosterone excretion. Moreover, plasma aldosterone levels and the simultaneously measured plasma renin activity were linearly correlated over a wide range of sodium balance, again pointing to a key role for renin in the control of plasma aldosterone levels. In 21 patients with normal renin essential hypertension, the absolute levels of plasma aldosterone and their relation to plasma renin levels were similar to those observed in normal subjects. In 14 patients with high renin hypertension concurrent plasma aldosterone levels were commensurately elevated. A deflection of this renin-aldosterone interaction observed in some high renin patients appeared consequent to potassium depletion. In contrast, in 14 of 16 patients with low renin essential hypertension, noon plasma aldosterone concentrations, under conditions of normal or moderately high dietary sodium, were higher relative to simultaneous plasma renin activity, resulting in an abnormal plasma aldosterone to renin ratio above 10. This abnormal renin-aldosterone interrelation could prove useful for identifying and further characterizing patients within the low renin hypertension category. In hypertensive patients, plasma aldosterone measurements can be used interchangeably with urinary aldosterone excretion rates but for full meaning they must still be related to an index of sodium balance such as the daily rate of sodium excretion. Moreover, they have special value for short-term studies and for evaluating aldosterone secretion in states of hepatic or renal insufficiency and perhaps in edematous states in which impaired aldosterone metabolism or renal excretion occurs.