A diurnal rhythm in plasma renin activity in man.

Abstract

Although it has been known for many years that the renin-angiotensin system is responsive to decreases in renal perfusion pressure (1-3), it was only recently discovered that angiotensin is an im-portant regulator of aldosterone secretion (4-6). Before it was known that angiotensin had a role in the regulation of aldosterone secretion, a large number of studies indicated that experimental or pathological conditions that resulted in a reduc-tion of effective blood volume would stimulate al-dosterone secretion (7). Studies have already been published indicating that plasma renin ac-tivity and aldosterone excretion both increase in response to sodium deprivation (8-10) and as-sumption of upright posture (11-13). In the course of studies attempting to correlate plasma renin activity with aldosterone excretion we found that the rises in plasma renin activity and in urinary aldosterone that occur after the assumption of upright posture early in the day are both of limited duration and that they diminish late in the day despite continued maintenance of upright posture (14). The observed afternoon fall in plasma renin activity is not readily ex-plained by existing knowledge of the physiology of renin secretion. The present study, therefore, focuses attention for the first time on the question of whether there might be a consistent diurnal rhythm in plasma renin activity. In order to characterize diurnal variations in plasma renin activity that might occur independently of dietary and postural in-*Submitted for publication March 15, 1966; accepted