Assessment of brain AT1-receptor on the nocturnal basal and angiotensin-induced thirst and sodium appetite in ovariectomised rats.

Objective: Considering the controversial data regarding the role of the brain renin-angiotensin system (RAS) on the thirst and sodium appetite in ovariectomised rats, we aimed to evaluate the role of the brain angiotensin II (Ang II) AT1-receptor on the nocturnal fluids intake.
Materials and Methods: Groups of Wistar female rats were ovariectomised and chronically given oestrogen or vehicle to evaluate its influence on effects induced by i.c.v. injection of losartan, Ang I and Ang II.
Results: The i.c.v. losartan decreased basal water intake in the ovariectomised group. Ang II but not Ang I-induced nocturnal dipsogenic and natriorexigenic responses in ovariectomised rats. In oestrogen-treated rats, both peptides increased fluids intake. Previously, i.c.v. losartan abolished these effects in all groups. Oestrogen replacement decreased the nocturnal fluids intake, attenuated the losartan and Ang II effects, and highlighted the Ang I response.
Conclusions: The present study has shown for the first time the involvement of AT1-receptor in regulating nocturnal basal water and salt intake in ovariectomised rats. In addition, our data have revealed an unexpected increased brain Ang I-mediated fluid intake in oestrogen-treated ovariectomised compared to ovariectomised rats, which was blocked by previous i.c.v. losartan. Our data have therefore shown that oestrogen influences homeostatic behaviours dependent on brain RAS.