Influence of the pituitary gland on sodium conservation, plasma renin and renin substrate concentrations in the rat.

Abstract

The responses of plasma renin and renin substrate concentrations to changes in dietary sodium intake have been investigated in normal and hypophysectomized rats. In the normal rat sodium deprivation for 13 days produced a striking increase in plasma renin concentration. However, unlike the response observed in other species, administration of 0.45 and 0.9 % sodium chloride in the drinking water failed to suppress the level of plasma renin below that observed in rats drinking 0.18% saline. No significant changes in plasma renin substrate concentration were induced by the various alterations in sodium intake. The changes observed in plasma renin concentration support the view that the renin-angiotensin system is involved in sodium conservation in the rat, perhaps in part via the stimulation of aldosterone secretion. In the hypophysectomized groups of animals similar changes in plasma renin concentration were observed in relation to changes in salt balance, indicating that the basic responsiveness of the system had not been modified. However, renin levels were slightly lower throughout in hypophysectomized animals but the differences were not significant. Hypophysectomy resulted in a significant fall in plasma renin substrate concentration. Other things being equal, the large fall in substrate concentration could be a major factor in reducing the circulating concentration of angiotensin II in vivo, and it might therefore be involved in the reduced aldosterone secretion described in sodium-depleted hypophysectomized animals. Whatever the effect of the pituitary upon, these interactions, the study indicates basically normal capacities for the hypophysectomized rat both to secrete renin and to conserve sodium under extremely rigorous conditions of stress. (Endocrinology86: 824, 1970)