Divergent effects of ER{alpha} and ER{beta} on fluid intake by female rats are not dependent on concomitant changes in AT1R expression or body weight

Estradiol (E₂) decreases both water and saline intakes by female rats. The ERα and ERβ subtypes are expressed in areas of the brain that control fluid intake; however, the role that these receptors play in E₂'s antidipsogenic and antinatriorexigenic effects have not been examined. Accordingly, we tested the hypothesis that activation of ERα and ERβ decreases water and saline intakes by female rats. We found a divergence in E₂'s inhibitory effect on intake: activation of ERα decreased water intake, whereas activation of ERβ decreased saline intake. E₂ decreases expression of the angiotensin II type 1 receptor (AT₁R), a receptor with known relevance to water and salt intakes, in multiple areas of the brain where ERα and ERβ are differentially expressed. Therefore, we tested for agonist-induced changes in AT₁R mRNA expression by RT-PCR and protein expression by analyzing receptor binding to test the hypothesis that the divergent effects of these ER subtypes are mediated by region-specific changes in AT₁R expression. Although we found no changes in AT₁R mRNA or binding in areas of the brain known to control fluid intake associated with agonist treatment, the experimental results replicate and extend previous findings that body weight changes mediate alterations in AT₁R expression in distinct brain regions. Together, the results reveal selective effects of ER subtypes on ingestive behaviors, advancing our understanding of E₂'s inhibitory role in the controls of fluid intake by female rats.

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