Kinetic of DNA synthesis in immature rat uterus: Age dependence and estradiol stimulation

Abstract

1. 1. The stimulation of DNA synthesis by estradiol-17β was studied in surving uteri of 1- to 30-day-old rats injected 24 h previously with estradiol-17β. 2. 2. Uteri from untreated immature rats showed an age-dependent decrease in incorporation of [ Me −3H]thymidine into DNA during the first month after birth; incorporation decreased by a factor of 10 over this period. 3. 3. In rats less than 15 days old, a single estradiol-17β injection did not result in an increase in the rate of DNA synthesis; uterine wet weight, RNA content and protein content also showed no increase. At 15 days, estradiol caused an increase in uterine wet weight, but only slight increases in the other parameters measured. In uteri of 20-day-old rats, estradiol-17β caused a significant increase in the rate of DNA synthesis and in RNA and protein content. 4. 4. Amounts of estradiol-17β as low as 50 pg per 20-day-old rat (33 g in weight) significantly increased the rate of DNA synthesis. Dibutyryl cyclic AMP, administered in doses of 0.5 mg into the uterine lumen or 5 mg intraperitoneally, showed no effect on uterine nucleic acid or protein synthesis. 5. 5. In the 20-day-old rat uterus, the epithelial, stromal and myometrial tissues all showed a wave of cell division with a peak mitotic activity between 24 and 28 h after estradiol injection. In the epithelium, the increase was from 3 mitoses per 1000 cells to 164 per 1000 cells 26 h after hormone treatment.