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

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.

Key Words: urethra, urinary incontinence, estrogens, raloxifene, levormeloxifene

Abbreviations and Acronyms: AR, adrenergic receptor, DMEM, Dulbecco's modified Eagle's medium, ER, estrogen receptor, FBS, fetal bovine serum, PBS, phosphate buffered saline, PCR, polymerase chain reaction, SERM, selective ER modulator, SUI, stress UI, UI, urinary incontinence, USMC, urethral smooth muscle cell