Purpose: We investigated the effect of estrogen, raloxifene and levormeloxifene on alpha1A-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 alpha1A-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 alpha and beta by immunofluorescence microscopy. Urethral smooth muscle cells were treated with estrogen, raloxifene or levormeloxifene for 24 hours and examined for alpha1A-adrenergic receptor expression by real-time polymerase chain reaction. The effects of these drugs on alpha1A-adrenergic receptor expression were further examined by promoter assays.
Results: Estrogen treatment resulted in decreased alpha1A-adrenergic receptor expression in the urethras. Urethral smooth muscle cells expressed estrogen receptors alpha and beta, the former predominantly in the cytoplasm and the latter in the nucleus. Estrogen significantly down-regulated alpha1A-adrenergic receptor mRNA expression, while raloxifene and levormeloxifene had no significant effect. Estrogen also significantly down-regulated alpha1A-adrenergic receptor promoter in the presence of estrogen receptor alpha or beta. Raloxifene and levormeloxifene up-regulated alpha1A-adrenergic receptor promoter in the presence of estrogen receptor alpha but not beta.
Conclusions: Estrogen down-regulated alpha1A-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.