ROLE OF BRAIN ANGIOTENSIN-II IN THIRST AND SODIUM APPETITE OF SHEEP

The contribution of brain angiotensin II (ANG II) to thirst and Na+ ap petite of sheep was evaluated. Thirst was stimulated by water deprivat ion, intracarotid or intracerebroventricular infusion of ANG II, or in tracarotid or intracerebroventricular infusion of hypertonic solution. Intracerebroventricular infusion, over 1-3 h, of the ANG II type 1 (A T(1)) receptor antagonist, losartan, decreased or abolished water inta ke caused by all of the stimuli tested. Intracerebroventricular infusi on of ZD-7155, another AT(1)-receptor antagonist, blocked ANG II-induc ed water intake. Neither losartan nor ZD-7155 infused intracerebrovent ricularly altered the Na+ appetite of Na+-depleted sheep. Intracerebro ventricular infusion of losartan over 3 h, however, did block the incr ease in water intake and the decrease in Nai intake caused by intracer ebroventricular infusion of hypertonic NaCl in Na+-depleted sheep. Int racerebroventricular infusion of the ANG II type 2 (AT(2)) receptor an tagonist, PD-123319, over 1-3 h, did not alter ANG II-induced water in take or Na+ depletion-induced Na+ intake. These results are consistent with the proposition that brain ANG II, working via AT(1) receptors, is involved in the neural system controlling some aspects of physiolog ical thirst and Na+ appetite. A role for AT(2) receptors in physiologi cal thirst or Na+ appetite is not supported by the present results.