Injections of phentolamine into the anterior hypothalamus-preoptic area of rats blocks both pressor and drinking responses produced by central administration of angiotensin II.

There are conflicting reports of a possible contribution of noradrenergic projections to the rostral hypothalamus to drinking and blood pressure regulation. The present study investigated the effects of injecting phentolamine into the anterior hypothalamus-preoptic region on drinking and blood pressure responses elicited by injecting angiotensin II into a lateral cerebral ventricle of the rat. Angiotensin II (250 ng or 25 ng) elicited water intakes averaging 9.25 +/- 0.52 ml and 4.35 +/- 0.44 ml respectively in 15 min with latencies of less than 3 min. Phentolamine, an alpha-adrenergic antagonist, injected into the rostral hypothalamus produced a dose-dependent reduction in water intake and number of laps taken accompanied by an increased latency to drink. In the urethane anaesthetized rat, angiotensin II produced significant increases in blood pressure. Injections of phentolamine into rostral hypothalamic sites in which drinking responses to angiotensin II were attenuated, also attenuated the pressor response to angiotensin II. These results indicate that alpha-adrenergic input to the rostral hypothalamus is involved in both the pressor and drinking responses elicited by central angiotensin II.