Estrogen replacement attenuates stress-induced pressor responses through vasorelaxation via β₂-adrenoceptors in peripheral arteries of ovariectomized rats.

We examined whether chronic estrogen replacement has an inhibitory effect on stress-induced pressor responses via activation of β₂-adrenoceptor (AR) in peripheral arteries of ovariectomized rats. Female Wistar rats aged 9 wk were ovariectomized. After 4 wk, pellets containing either 17β-estradiol (E₂) or placebo (Pla) were subcutaneously implanted into the rats. After 4 wk of treatment, rats underwent cage-switch stress, and, in a separate experiment, a subset received an infusion of isoproterenol (ISO) with or without pretreatment with the β₁-AR blocker atenolol or the β₂-AR blocker butoxamine. In addition, the isolated mesenteric artery was used to assess the concentration-related relaxing responses to ISO and the β₁- or β₂-AR mRNA level. The cage-switch stress-induced pressor response was significantly attenuated in the E₂-treated group compared with the Pla-treated group. Pretreatment with atenolol reduced blood pressure responses in both groups. However, butoxamine enhanced the pressor response only in the E₂-treated group, resulting in no difference between the two groups. In addition, the intravenous ISO-induced depressor response was significantly enhanced in the E₂-treated group compared with the Pla-treated group. Furthermore, the difference in the depressor response was abolished by pretreatment with butoxamine but not by atenolol. In the isolated mesenteric artery, butoxamine caused a rightward shift in ISO-induced concentration-related relaxation in the E₂-treated group. The β₂-AR mRNA level in the mesenteric artery was higher in the E₂-treated group than in the Pla-treated group. These results suggest that estrogen replacement attenuated the stress-induced pressor response probably by suppressing vasoconstriction via activation of β₂-ARs in peripheral arteries of ovariectomized rats. NEW & NOTEWORTHY In this study, we show, for the first time, that estrogen replacement has an inhibitory effect on the psychological stress-induced pressor response through vasorelaxation via β₂-adrenoceptors, probably due to overexpression of β₂-adrenoceptor mRNA, in peripheral arteries of ovariectomized rats.

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