Expression of oestrogen receptor-α and -β in ovarian endometriomata

The contribution of oestrogen receptor (ER) isoforms, ER-alpha and ER-beta, in oestrogen-dependent development and growth of ovarian endometriomata, is unknown. Therefore, we examined the expression of ER-alpha and ER-beta in ovarian endometriomata and normal uterine endometrium. ER-alpha and ER-beta were shown to be dominantly expressed in the nuclei of the epithelial lining cells of ovarian endometrioma and of the glandular cells of normal uterine endometrium. ER-beta was expressed at a much lower level than ER-alpha in the glandular cells of normal uterine endometrium, while ER-beta was expressed at a slightly lower level than ER-alpha in the epithelial lining cells of ovarian endometrioma. In normal uterine endometrium, ER-beta mRNA was expressed at a much lower level than ER-alpha mRNA, and the expression pattern of ER-beta mRNA during the menstrual cycle was similar to that of ER-alpha mRNA. On the other hand, ER-beta mRNA expression was significantly higher and over a much greater range in ovarian endometriomata (P < 0.05) than in normal uterine endometrium during the menstrual cycle, while ER-alpha mRNA expression was relatively lower and more random. Therefore, in ovarian endometriomata, oestrogen action via ER-alpha cascades seems to be partially damaged, as the expression of ER-alpha mRNA does not respond to endocrinological alterations during the menstrual cycle, while the relative over-expression of ER-beta might be related to a unique oestrogen-dependent growth and spreading of ovarian endometriomata.