Effects of hypotension and fluid depletion on central angiotensin-induced thirst and salt appetite

We examined the effects of hypotension and fluid depletion on water and sod ium ingestion in rats in response to intracerebroventricular infusions of A NG II. Hypotension was produced by intravenous infusion of the vasodilator drug minoxidil (25 mug.kg(-1).min(-1)) concurrently with the angiotensin-co nverting enzyme inhibitor captopril (0.33 mg/min) to prevent endogenous ANG II formation. Hypotension increased water intake in response to intracereb roventricular ANG II (30 ng/h) but not intake of 0.3 M NaCl solution and ca used significant urinary retention of water and sodium. Acute fluid depleti on was produced by subcutaneous injections of furosemide (10 mg/kg body wt) either alone or with captopril (100 mg/kg body wt sc) before intracerebrov entricular ANG II (15 or 30 ng/h) administration. Fluid depletion increased water intake in response to the highest dose of intracerebroventricular AN G II but did not affect saline intake. In the presence of captopril, fluid depletion increased intakes of both water and saline in response to both do ses of intracerebroventricular ANG II. Because captopril administration cau ses hypotension in fluid-depleted animals, the results of the two experimen ts suggest that hypotension in fluid-replete animals preferentially increas es water intake in response to intracerebroventricular ANG II and in fluid- depleted animals increases both salt and water intake in response to intrac erebroventricular ANG II.