Effects of Estrogen, Raloxifene and Levormeloxifene on α1A-Adrenergic Receptor Expression

Abstract

Purpose: We investigated the effect of estrogen, raloxifene and levormeloxifene on α1A-adrenergic receptor expression. Materials and Methods: Postpartum rats underwent intravaginal balloon injury and ovariectomy, and were then treated with estrogen or placebo for 8 weeks. The urethras were examined for α1A-adrenergic receptor expression by Western blot analysis and immunohistochemistry. Urethral smooth muscle cells were isolated from untreated female rats and examined for the expression of estrogen receptors α and β by immunofluorescence microscopy. Urethral smooth muscle cells were treated with estrogen, raloxifene or levormeloxifene for 24 hours and examined for α1A-adrenergic receptor expression by real-time polymerase chain reaction. The effects of these drugs on α1A-adrenergic receptor expression were further examined by promoter assays. Results: Estrogen treatment resulted in decreased α1A-adrenergic receptor expression in the urethras. Urethral smooth muscle cells expressed estrogen receptors α and β, the former predominantly in the cytoplasm and the latter in the nucleus. Estrogen significantly down-regulated α1A-adrenergic receptor mRNA expression, while raloxifene and levormeloxifene had no significant effect. Estrogen also significantly down-regulated α1A-adrenergic receptor promoter in the presence of estrogen receptor α or β. Raloxifene and levormeloxifene up-regulated α1A-adrenergic receptor promoter in the presence of estrogen receptor α but not β. Conclusions: Estrogen down-regulated α1A-adrenergic receptor expression in the urethral smooth muscle of female rats, while raloxifene and levormeloxifene had no significant effect. These findings represent a possible molecular mechanism through which estrogen, raloxifene and levormeloxifene differentially affect urinary continence.