Although a clear role for estrogen receptor (ER) α has been established, the contribution of ERβ in estrogen-dependent development, growth and functions of the myometrium is not understood. As a first step towards understanding the role of ERβ, we have examined the expression of ERα and ERβ in the human myometrium. With competitive RT-PCR assays, the level of ERβ mRNA was 10-200 times lower than that of ERα mRNA in both premenopausal and postmenopausal myometrium. In premenopausal myometrium, the expression pattern of ERβ mRNA during the menstrual cycle was similar to that of ERα mRNA, with highest levels in peri-ovulatory phase. In postmenopausal myometrium, ERβ mRNA was significantly higher than it was in premenopausal myometrium, while the level of ERα mRNA was lower. The net result was a change in the ratio of ERβ to ERα mRNA expression. The ratio changed from 0.6-1.5 in premenopausal to 2.5-7.6 in postmenopausal myometrium. In premenopausal women, the gonadotropin releasing hormone analogue, leuprorelin acetate, elicited a decrease in ERα and an increase in ERβ mRNA expression to cause a postmenopausal receptor phenotype. Estradiol, on the other hand, reversed ERα and ERβ mRNA expression and their ratio in postmenopausal myometrium to those of premenopausal myometrium. Immunohistochemical staining and Western blot analysis of ERα and ERβ with semiquantitative analysis showed good agreement between mRNA and protein levels. The data indicate that coordinated expression of ERα and ERβ might be necessary for normal estrogen action in myometrium. Furthermore, estrogen appears a dominant regulator of both receptors in the myometrium. © 2002 Elsevier Science Inc. All rights reserved.
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