Cellular localization of aromatase in human endometrium

The expression of aromatase was examined in human endometrium throughout the menstrual cycle, early pregnancy, and ovarian endometriosis with a specific monoclonal antiserum to human purified placental aromatase cytochrome P-450 (P-450AROM). Tissues were obtained from women undergoing hysterectomy, oophorectomy and/or intrauterine curettage. The day of the cycle was determined from the onset of the last menstrual period and confirmed by endometrial histology. In secretory endometrium, stronger immunoreactivity of aromatase was observed in epithelial gland than immunoreactivity of stroma, especially in mid and late secretory endometrium. In endometrium of early pregnancy, significant immunoreactivity was seen in both glandular cells and stromal cells. However, weak immunoreactivity was seen only in epithelial gland of ovarian endometriosis. There was no immunoreactivity in atrophic endometrium or late proliferative endometrium. These results show that the physiological action of endometrial aromatase is modulated by progesterone and equipped with the capacity for cyclic change throughout the menstrual cycle. The presence of aromatase in the ovarian endometriosis is of interest, since it is histologically different from normal cyclic endometrium, and this is consistent with the ability to synthesize estradiol. But the weak intensity in endometriosis probably means that only a small amount of estradiol was synthesized, which served to explain the poor response to GnRHa or danazol administered on ovarian cystic endometriosis.