We previously reported that activin A, not inhibin, was localized to endometrial tissues, and that the endometrium might be a major source of activin A during the menstrual cycle, using an immunohistochemical method. However, there are few detailed reports concerning the expression of inhibin subunits, activin receptors and Smad proteins in the ectopic endometrial tissues of endometriosis. In this study, our purpose was to evaluate the immunohistochemical localization of inhibin α-, βA-subunits, activin A, activin receptor, and Smad proteins in ovarian endometriosis. Tissue samples from ovarian endometriosis were obtained from 13 women. Normal endometrial tissues were obtained during the proliferative phase from 5 premenopausal women without endometriosis who were undergoing a hysterectomy for the treatment of uterine cervical intraepithelial neoplasia 3. We examined the immunohistochemical localization of inhibin/activin α-, βA-subunit, activin A, activin receptors types IA, IB, IIA, IIB, Smad2, Smad3 and Smad4 using an avidin-biotin-peroxidase complex technique. No immunostaining for the α-subunit of inhibin was observed in ovarian endometriosis and the normal endometrium. Positive immunostaining for the βA-subunit of inhibin, activin A, activin receptors types IA, IB, IIA, IIB, Smad2, Smad3 and Smad4 was observed in ovarian endometriosis and the normal endometrium. In conclusion, these results suggest that activin A, but not inhibins, is produced by ovarian endometriosis and the normal endometrium, and that the activin signal transduction system exists in both ovarian endometriosis and the normal endometrium.

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