Urinary aldosterone excretion rate and plasma aldosterone concentration in the rat: effect of ACTH, DOC, furosemide and of changes in sodium balance.

In rats kept under standard conditions urinary aldosterone exretion rate (UAER) and plasma aldosterone concentration (PAC) showed a circadian rhythm with peak values at the beginning of the dark perioith a single dose of DOC (2 mg/kg sc) or given saline as drinking water UAER and PAC decreased to very low levels. Restriction of dietary sodium for 5 weeks increased UAER and PAC 60-fold and 100-fold, respectively. Treatment with ACTH (250 or 500 microng/kg iv) stimulated UAER 8 h following injection and PAC 1 h after injection. In rats treated with a single dose of furosemide (25 mg/kg sc) PAC increased to maximal values within 90 min and reached control values within 24 h. Twenty-four hours-UAER also increased after furosemide treatment. UAER paralleled PAC under all experimental conditions tested. Therefore, our results suggest that UAER is a reliable index of the activity of the renin-angiotensin-aldosterone system in rats under conditions of low and high aldosterone secretion. Measurement of UAER is a useful tool for studies on aldosterone levels in rats over a long period of time.