Alterations in aldosterone secretion and metabolism in low renin hypertension

Low renin essential hypertensives (LRH) have normal plasma aldosterone levels which are inappropriately high in relation to their PRA. Posture is the major determinant for plasma aldosterone and PRA levels, but it is not known whether postural increments (delta) of plasma aldosterone and (delta) PRA are also abnormal in LRH. To evaluate this, LRH (n = 8), normal renin hypertensives (NRH; n = 9), normotensive controls (n = 18), and subjects with idiopathic hyperaldosteronism (IHA; n = 5) were studied in a metabolic unit on a controlled diet over 7 days. Overnight supine and 4-h upright PRA, plasma aldosterone, and 24-h urinary tetrahydroaldosterone (THA) and aldosterone secretion rates (ASR) were measured. The delta in plasma aldosterone after 4 h of upright posture was not different in the four groups. The ratio of delta plasma aldosterone/delta PRA, however, was elevated in both IHA and LRH compared to that in NRH and normals. THA excretion was also elevated in IHA and LRH, but LRH had a normal ASR. This resulted in a higher fractional THA excretion (THA/ASR) in LRH compared to the other three groups. These data further support enhanced adrenal angiotensin-II sensitivity in LRH. Aldosterone was preferentially metabolized to THA in LRH. Since THA has reduced biological activity, this may be a compensatory mechanism to reduce mineralocorticoid activity in LRH.