Renin and Aldosterone Secretion in Man as Influenced by Changes in Electrolyte Balance and Blood Volume

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Abstract
In six normal volunteers maintained on a constant dietary intake, serial studies were made of plasma renin activity, blood volume, aldosterone secretion and sodium balance, first following dietary and diuretic-induced depletion of sodium and blood volume, then following a period of sodium repletion during a maintained reduction in blood volume, and finally after blood volume repletion. In the first phase, during which depletion of blood volume paralleled sodium depletion, renin and aldosterone secretion were both increased. Under the circumstances of a subsequent study period, however, it was possible to separate the effects of sodium depletion from those of reduction in total blood volume. In this period, the administration of sodium chloride was associated with an increased urinary sodium excretion and a marked suppression of plasma renin and aldosterone secretion at a time when total blood volumes were maintained below control values by repeated plasmapheresis and phlebotomy. This sodium-dependent suppression of renin and aldosterone secretion may have been mediated by an expansion in extravascular fluid volume(s). However, the observed effects are perhaps better explained in terms of an induced change in intrarenal tubular sodium transport. The parallelism observed between the changes in renin and aldosterone secretion suggests that under the conditions of these studies renin plays a major role in regulating aldosterone secretion.