Antagonism of the dipsogenic action of intraseptal angiotensin II in the rat

Abstract The injection of 0.01 to 2.0 μg of antiotensin II (A II) into the medial septal area of unanesthetized rats in normal water balance caused dose-dependent drinking, during the 60 min period following drug administration. A hyperbolic dose-response curve, rectified by a log dose scale was obtained. Pretreatment with 5 and 10 μg of locally injected haloperidol, 15 min prior to A II (0.3 μg), partially antagonized the dipsogenic effects of A II and a dose of 25 μg of haloperidol completely blocked this effect. A cataleptic-like state followed haloperidol administration. The injection of doses as high as 25 μg of dopamine in the same brain site caused no drinking. Pretreatment with 3 μg of intraseptal Sar 1 , Ala 3 , Ile 8 — angiotensin I, a competitive antagonist of A II at peripheral receptors, completely antagonized the dipsogenic effect of A II. The same dose (3 μg) of the A II analog alone caused only a mild but significant drinking response. These results suggest that A II acts of specific receptors in the CNS that may be similar to peripheral angiotensin receptors. On the other hand, the role of brain catecholamines in the mediation of A II-induced drinking remains uncertain.