Influence of captopril on fluid and electrolyte balances and adrenocortical responses during sodium deprivation in the rat.

An angiotensin I-converting enzyme inhibitor (captopril) was given by gastric lavage at a dose of 30 mg/kg body weight per day to Long-Evans rats for a 13-day period during which they received a sodium-deficient diet. This regime was preceded by a 3-day period during which measurements were made on the animals on a sodium-replete dietary intake. Control sodium-deprived rats showed increased plasma renin activities, increased peripheral aldosterone concentrations and reduced urinary sodium excretion; they maintained positive sodium balance and the zona glomerulosa of the adrenal cortex hypertrophied. Captopril-treated sodium-deprived rats failed to reduce urinary sodium excretion sufficiently and entered a period of marked and sustained negative sodium balance. Peripheral aldosterone concentrations after 12 days of sodium deprivation in the presence of captopril treatment were similar to those of sodium-replete rats. The adrenocortical zona glomerulosa of the captopril-treated rats did not increase in size and regressive changes were noted.