MITOTIC ACTIVITY OF VAGINAL EPITHELIAL CELLS FOLLOWING NEONATAL INJECTIONS OF DIFFERENT DOSES OF ESTROGEN IN MICE

In C57Black/Tw mice given injections of 1 μg estradiol‐17β (E) for 5 days beginning on the day of birth, and killed a few days after the treatment, the vaginal epithelium showed estrogen‐dependent proliferation and parakeratosis. In contrast, in the mice treated neonatally with 30 μg E for 5 days, the vaginal epithelium exhibited estrogen‐independent proliferation and cornification or parakeratosis. Two peaks occurred in the mitotic rate in vaginal epithelial cells in the proximal and middle vaginae of the 1 μgE‐treated mice, at 1 and 5 days of age, respectively, while the first peak was lacking in the distal vagina. The mitotic activity in 1 μgE‐treated mice declined to the control level at 60 days. In the 30 μgE‐treated animals also, 2 peaks were found in the mitotic rate at 1 and 7 days in both the proximal and middle vaginae. In contrast to the 1 μgE‐treated mice, although the rate dropped once at 10 days, it increased again at 20 days and remained high thereafter. The second peak at 7 days of age coincided with the active proliferation of nodules appearing in the 30 μgE‐treated mice. In the distal vagina, a peak occurred in the mitotic rate at 7 days without a preceding peak like that observed in the other parts of the vagina following the first injection of E on the day of birth.