Low Renin, “Normal” Aldosterone and Hypertension: Circadian Rhythm of Renin, Aldosterone, Cortisol and Growth Hormone

The upright and supine circadian rhythms of plasma renin activity (PRA), plasma aldosterone (PA), plasma cortisol (PC), and serum growth hormone (GH) were determined in 7 normals and 12 patients with hypertension, low PRA, and normal aldosterone excretion (LRH = low renin hypertension). In general PRA was always lower in LRH than in normals. However, PA in LRH was essentially normal. The average PC was greater in LRH than in normals and there were some differences between normals and LRH in the circadian rhythm of PC. Levels and patterns of growth hormone were not different between the two groups. A probable circadian rhythm of plasma aldosterone was demonstrated in normals and in LRH both in the upright and recumbent positions. Under these circumstances the higher plasma aldosterone noted in the morning than in the evening was not associated with changes in the mean circulating levels of PRA. However, significant decreases in PC were found from morning to evening. This suggests a possible role for ACTH in the control of aldosterone production not only in normals but also in patients with LRH. However, the factor maintaining normal aldosterone production in LRH does not appear to be either PC or GH. Unusual sensitivity of the adrenal gland to circulating levels of PRA may be at least partially responsible since PRA and PA were highly correlated. Finally, during prolonged recumbency, PRA and PC in normal subjects were similar to values in LRH, but PA was clearly greater than normal, demonstrating higher aldosterone levels in LRH compared to normals.