Local danazol therapy can improve endometriotic signs and symptoms without causing any menstrual disorders. As a consequence, certain direct actions of danazol on endometriotic tissues have been proposed, but the mechanisms of these actions have not been clarified. In the present study, the direct effects of danazol on normal human endometrial stromal cells (ESCs) were examined using in vitro decidualization assays. Danazol did not affect the viable cell numbers of unstimulated ESCs or 8Br-cAMP-stimulated decidualized ESCs, but significantly enhanced the viable cell numbers of 8-Br-cAMP-stimulated ESCs during decidualization in a dose-dependent manner. Danazol had no effect on PRL secretion by 8-Br-cAMP-stimulated decidualized ESCs. Danazol, as well as progesterone and medroxyprogesterone acetate (MPA), induced ESC decidualization. Danazol synergistically enhanced the differentiation process of 8-Br-cAMP-stimulated ESCs during decidualization. Although progesterone and MPA increased G-CSF and IL-8 secretion by ESCs in similar manner to 8-Br-cAMP, danazol had no such effects. Moreover, remarkable increases in G-CSF and IL-8 secretions by 8-Br-cAMP-stimulated ESCs during decidualization were completely inhibited by cotreatment with danazol. These results indicate that danazol has specific pharmacological effects on ESCs, rather than progesterone-like effects or similar effects to those reported for endometrial cytokines. According to the results, normal human ESCs can be classified into at least four functional subpopulations. Therefore, under certain circumstances, danazol has similar or opposite effects on ESCs to certain endometrial cytokines, suggesting that it regulates functional cellular subpopulation ratios of normal human ESCs by modifying the endometrial cytokine network in endometrial stromal tissues.

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