Renin-Aldosterone System in Osmoregulatory Reactions of Healthy Subjects in Response to Desmopressin

Systemic regulation of osmotic and ionic homeostasis was studied in healthy male volunteers after oral administration of desmopressin. Endogenous secretion of the antidiuretic hormone was inhibited by a water load (WL, 2% of the body mass). Desmopressin exerted an antidiuretic effect. In addition, the WL portion excreted during 4 h decreased and the urine osmolality at peak diuresis increased with the absence of osmotically free water. At maximum diuresis, the ratio between concentrations of osmotically active substances in the urine and in the blood was high, which reflected an intense antidiuretic effect. Desmopressin progressively decreased the rate of sodium excretion owing to a change of sodium reabsorption in the kidneys. The WL increased the level of aldosterone and the activity of renin in blood plasma 1.5 h after its administration. Contrary to the control series, desmopressin stimulated the renin-angiotensin-aldosterone system only by the end of the 4-h observation period. A significant negative correlation between the aldosterone level and the rate of sodium excretion was observed 3 h after the beginning of testing (r = ?0.76). Thus, under conditions of water loading, desmopressin had a specific antidiuretic effect involving systemic mechanisms of ion regulation.