Different expression of estrogen receptors alpha and beta in human myometrium and leiomyoma during the proliferative phase of the menstrual cycle and after GnRHa treatment.

Uterine leiomyomas (uterine fibroids) are sex-steroid dependent benign tumors. Limited knowledge is available regarding the role of estrogen and their receptors in the regulation of fibroids in premenopausal women, and in their shrinkage after treatment with a gonadotropin-releasing hormone analogue (GnRHa). The expression of the two subtypes of the estrogen receptor (ER), ERalpha and ERbeta was studied in leiomyoma and homologous myometrium from women in the proliferative phase of the menstrual cycle and from women treated with GnRHa. The mRNA levels of ERalpha and ERbeta were monitored by solution hybridization and in situ hybridization, and receptor proteins were detected and localized by immunohistochemistry. Both ERalpha and ERbeta were present in the leiomyomas and homologous myometrium. The ERalpha mRNA level in the leiomyomas was higher than in the surrounding myometrium. The ERbeta mRNA level was lower than that of ERalpha in both groups. ERbeta immunoreactivity was lower in leiomyomas when compared with the myometrium after GnRHa treatment, while ERalpha was higher in the leiomyomas. The present results imply that the increased ratio of ERalpha/ERbeta observed in the fibroids after GnRHa treatment could reflect or be the cause of the shrinkage of the leiomyoma, which is the clinical outcome of this treatment.