Effects of prenatal treatment with estrogen on mitotic activity of vaginal anlage cells in mice.

Female fetuses of C57BL/Tw mice were injected subcutaneously with 50 microgram 17 beta-estradiol on day 17 of fetal life. The treatment was proved to induce ovary-independent proliferation and cornification in the vaginal epithelium in later postnatal life. These fetuses were sacrificed on day 19 or 20, or on the 3rd day after birth. Histological observation on day 19 or 20 of fetal life did not show a particular effect of estrogen at any portion of the vaginal anlage, but at 3 days after birth, the epithelium of the Müllerian vagina in estrogen treated females consisted of a single layer of columnar cells, whereas that in controls had double-layered columnar cells. A study of the mitotic rate revealed that the epithelial cells of the Müllerian vagina as well as those of the cervix were dividing more actively in fetuses than in pups. Estrogen injection on day 17 induced a marked suppression of the mitotic rate in the epithelium of the Müllerian vagina and cervix on day 19 and 20. On the other hand, estrogen treatment caused a significant increase in the mitotic rate of the epithelium of the sinus vagina, at least on days 19 and 20. It was concluded that the epithelial cells of the sinus vagina respond positively to estrogen and thus possibly play the main role of the development of irreversible changes in the vagina.