Inhibition of angiotensin-induced water intake following hexamethonium pretreatment in the dog

Abstract The possibility that the pressor effects of angiotensin II influence angiotensin-induced thirst was investigated in dogs pretreated with hexamethonium. Ganglionic blockade reduced drinking elicited by i.c.v. administration of angiotensin II and totally eliminated drinking elicited by i.v. infusion of angiotensin II, whereas the pressor response to i.v. and i.c.v. angiotensin II was significantly increased. In contrast, hexamethonium had no effect on water intake or mean arterial blood pressure following i.c.v. isoproterenol, and produced a significant increase in drinking to s.c. isoproterenol, which was preceded by a large fall in mean arterial pressure. No changes in mean arterial pressure or drinking were observed during NaCl infusion in hexamethonium-pretreated animals. These results suggest that angiotensin II exerts its full dipsogenic activity only during normotensive or hypotensive states, and that the pressor effect of angiotensin II can antagonize its effects on water intake.