Renin-angiotensin, arterial blood pressure, and salt appetite in rats

Simultaneous administration of the diuretic furosemide (10 mg/kg sc) and a low dose of the angiotensin-converting enzyme inhibitor captopril (5 mg/kg sc) reduced mean arterial blood pressure (MAP) and increased ingestion of water and 0.3 M NaCl within 2 h. Administration of either agent alone did not reduce MAP or cause significant fluid intakes. The increased ingestion of water and saline after furosemide plus captopril 1) was not due to increased excretion of water and sodium compared with losses after furosemide alone, 2) was abolished by the AT1-receptor blocker, losartan (10 mg/kg sc), and 3) was abolished by administration of a greater dose of captopril (100 mg/kg sc). Intravenous infusion of phenylephrine (3-4 micrograms.kg-1 x min-1) prevented the reduction in MAP after furosemide plus captopril and blunted the saline intake but not water intake. Simultaneous administration of the vasodilator minoxidil and captopril also stimulated robust salt appetite in association with reduced MAP. It is concluded that the integrity of renin-angiotensin mechanisms is necessary for the rapid ingestion of water and saline after furosemide and captopril and that arterial pressure modulates the behavioral responses.