Water and salt intake of wild rabbits (Oryctolagus cuniculus (L)) following dipsogenic stimuli.

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Wild rabbits trapped in their natural habitat and adapted to laboratory conditions were studied. Food, water and electrolyte (0.5 M-NaCl, 0.5 M-KCl, 0.25 M-MgCl2 and 0.25 M-CaCl2) consumption, urinary volume and sodium losses were monitored daily following stimuli which were found dipsogenic in other species. Water drinking was observed immediately after the intravenous injection of 1 M-NaCl (3 ml/kg), and following withdrawal of a mean of 13.9% of calculated blood volume. Daily intake of water decreased during intracerebroventricular (I.C.V.) infusion of 0.3 M-NaCl in artificial cerebrospinal fluid (c.s.f.), during I.C.V. infusion of 0.9 M-mannitol c.s.f., both at a rate of 17 microliters/h, following peritoneal dialysis with 5% (w/v) glucose solution, and during food restriction. Water intake was not affected following intravenous administration of acetazolamide (10 mg/kg). Daily intake of 0.5 M-NaCl solution was increased following peritoneal dialysis with 5% (w/v) glucose solution, which caused hyponatraemia, but not after haemorrhage which caused about the same sodium deficit as peritoneal dialysis, but as an isosmotic loss. Administration of two different angiotensin II analogues, systemically or I.C.V., failed to induce water drinking. However, urinary sodium excretion and intake of 0.5 M-NaCl were increased during the 5 days of I.C.V. infusion of angiotensin II (10 pmol/h). Infusion for 1 day of angiotensin II (500 pmol/h) led to increased urinary sodium excretion which was followed by increased intake. The intake of other electrolyte solutions was not significantly affected by any of the treatments detailed above. The mechanisms participating in initiation of thirst in wild rabbits are very sensitive to decrease in blood volume, in contrast to other species studied in laboratories. Angiotensin II at the doses and routes administered was not dipsogenic in wild rabbits. The increased intake of 0.5 M-NaCl solution observed during and after the long-term intraventricular administration of angiotensin II in the wild rabbit appears predominantly a response to sodium deficit caused by natriuresis. The persistence of appetite after the cessation of infusion is indicative of a residual effect on central mechanisms of salt appetite.

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