Studies from our lab and others show that oestrogen reduces angiotensin II (ANGII) induced water intake by ovariectomized rats. Elimination of endogenous oestrogen by ovariectomy causes weight gain that can be reversed or prevented by oestrogen replacement. Changes in body weight modify cardiovascular responses to ANGII but whether such changes have similar effects on central and behavioral responses to ANGII is unknown. The goal of this study was to evaluate the contributions of oestrogen and weight loss on isoproterenol (ISOP) induced Fos immunoreactivity (IR) and on angiotensin type 1 (AT1) receptor mRNA in forebrain regions implicated in the control of fluid balance. Isoproterenol significantly increased Fos IR in the hypothalamic paraventricular and supraoptic nuclei, the subfornical organ (SFO), and the organum vasculosum of the lamina terminalis, but had no effect on AT1 mRNA expression. However, both ISOP-induced Fos IR and the AT1 mRNA were attenuated in the SFO of the oestrogen and weight loss groups compared to that of the control group. Consequently, we examined the effect of weight loss on ISOP-induced water intake and plasma renin activity (PRA) and found that weight loss decreased water intake after ISOP, but had no effect on PRA. Thus, we propose that weight loss decreases ANGII-elicited water intake in the female rat by down regulating the expression of the AT1 receptor.