Angiotensin-estrogen interaction in female brain reduces drinking and pressor responses

Water intake fluctuates over the estrous cycle in rats, with daily intake lowest on the day of estrus. Since estrogen levels are highest preceding estrus and since the brain integrates thirst behavior, a possible central action of estrogen on fluid regulatory mechanisms was investigated in adult male and ovariectomized female rats. Ad libitum drinking was not changed the day of intracerebroventricular injection of estradiol benzoate (EB) but was significantly depressed the following day in females only. Drinking induced by intracerebroventricular angiotensin but not carbachol or cellular dehydration was also depressed in females the day after central EB treatment; again, no change occurred in males. To determine whether central EB depressed other centrally mediated responses to angiotensin, pressor responses to intracerebroventricular injections of angiotensin, carbachol, and hypertonic NaCl were also assessed. Only angiotensin-induced pressor responses in females were attenuated by central EB treatment, with a time course similar to that observed for the depression of drinking. We conclude that central regulatory responses to angiotensin are modulated by estrogen in female but not male brains.