Estrogen-Induced Vasoprotection Is Estrogen Receptor Dependent

Abstract

Background —Previous studies have shown that estrogen (E2) is vasoprotective in multiple animal models of vascular injury, including mice with homologous disruptions of either the α or β isoforms of the estrogen receptor (ER) gene, calling into question the ER dependency of the vasoprotective effect. This study used ICI 182,780, a nonselective ER antagonist, to test the hypothesis that the vasoprotective effect of E2 in the rat carotid injury model is ER mediated. Methods and Results —Intact female Sprague-Dawley rats were divided into 4 groups and treated with the nonselective ER antagonist ICI 182,780 (ICI; 0.5, 1.5, or 5 mg · kg −1 · d −1 , subcutaneously [S.C.]) or vehicle, beginning before balloon injury of the right common carotid artery and continuing for 14 days afterward. Four groups of ovariectomized rats (OVX) were treated with 17β estradiol (E2) (20 μg · kg −1 · d −1 , S.C.) alone or combined with ICI 5 mg · kg −1 · d −1 , S.C.; with ICI 5 mg · kg −1 · d −1 alone; or with vehicle according to a similar protocol. Two weeks after injury, rats were killed, and the carotid arteries were evaluated for neointima formation using morphometric analysis. ICI 182,780 blunted the E2-related protective effect and increased neointima formation in injured carotid arteries of intact female rats in a dose-dependent fashion. ICI had no effect on neointima formation in OVX, but addition of ICI to E2 in OVX blocked the inhibitory effect of exogenous E2 on neointima formation. Conclusions —These results indicate that the vasoprotective effect of E2 in the balloon-injured rat carotid artery model is mediated by ER.