Arousal of a specific and persistent sodium appetite in the rat with continuous intracerebroventricular infusion of angiotensin II.

Abstract

Prolonged exposure of the brain of the normal Na-replete rat to angiotensin II produced a marked and persistent Na appetite. Short-term, repeated systemic injections of isoprenaline or renin (both of which raise circulating angiotensin levels), and repeated intracranial injections of angiotensin II evoked increased ingestion of 2.7% NaCl. In a 2nd series of experiments, continuous infusions of angiotensin II directly into the brain evoked extremely large intakes of 3% NaCl. In addition to large intakes of hypertonic NaCl some rats drank daily volumes of water that exceeded their body weight. Not only did the animals drink large volumes of 3% NaCl during continuous angiotensin II infusion, but after termination of the infusion they continued to ingest NaCl at a rate comparable to that of the adrenalectomized rat. In most of the animals the persistent NaCl intake diminished over several days, but other animals continued to drink NaCl for as long as their intake was measured (up to 7 mo.). The response to continuous infusion infusion of angiotensin II was dose-dependent. Both water and 3% NaCl intake increased over a dose range of 6 ng/h to 6000 ng/h. The persistence of the Na appetite was also dose-dependent across the same range of doses. Angiotensin-induced salt appetite is specific for Na. Animals did not drink 0.5 M-NH4Cl and only occasionally drank minimal amounts of 0.5 M-KCl during continuous infusion. The large water turnover was not responsible for the Na appetite. Rats given access to 3% NaCl only during infusion of angiotensin drank copiously. Animals that were not infused but were given saccharine-flavored water to increase their water intakes did not drink 3% NaCl offered at the same time even though fluid intake was high. Rats that did not receive intracranial infusions but were infused intragastrically with volumes of water equal to or exceeding the amounts that were drunk during angiotension infusion did not drink the 3% NaCl but did drink some water. The onset of drinking after the start of angiotensin infusion varied from animal to animal. NaCl drinking was not temporally linked to water intake, although this was observed occasionally. Most of the drinking occurred during the night although angiotensin was infused continuously throughout the nychthemeron. Increases in angiotensin levels, probably with other factors such as increased levels of aldosterone or ACTH, result in Na appetite. The hormonal changes may alter the animals'' preception of salt making it more acceptable. By means that are not yet understood the increased acceptability of salt persists after the termination of angiotensin infusion.