Estrogen Reduces Aldosterone, Upregulates Adrenal Angiotensin II AT₂ Receptors and Normalizes Adrenomedullary Fra-2 in Ovariectomized Rats

We studied the effect of ovariectomy and estrogen replacement on expression of adrenal angiotensin II AT₁ and AT₂ receptors, aldosterone content, catecholamine synthesis, and the transcription factor Fos-related antigen 2 (Fra-2). Ovariectomy increased AT₁ receptor expression in the adrenal zona glomerulosa and medulla, and decreased adrenomedullary catecholamine content and Fra-2 expression when compared to intact female rats. In the zona glomerulosa, estrogen replacement normalized AT₁ receptor expression, decreased AT1B receptor mRNA, and increased AT₂ receptor expression and mRNA. Estrogen treatment decreased adrenal aldosterone content. In the adrenal medulla, the effects of estrogen replacement were: normalized AT₁ receptor expression, increased AT₂ receptor expression, AT₂ receptor mRNA, and tyrosine hydroxylase mRNA, and normalized Fra-2 expression and catecholamine content. We demonstrate that the constitutive adrenal expression of AT₁ receptors, catecholamine synthesis and Fra-2 expression are partially under the control of reproductive hormones. Our results suggest that estrogen treatment decreases aldosterone production through AT₁ receptor downregulation and AT₂ receptor upregulation. AT₂ receptor upregulation and modulation of Fra-2 expression may participate in the estrogen-dependent normalization of adrenomedullary catecholamine synthesis in ovariectomized rats. The AT₂ receptor upregulation and the decrease in AT₁ receptor function and in the production of the fluid-retentive, pro-inflammatory hormone aldosterone partially explain the protective effects of estrogen therapy.