Proliferative pattern of uterine cells from birth to adulthood in intact, neonatally castrated, and/or adrenalectomized mice, assayed by incorporation of [125I]iododeoxyuridine.

The proliferative pattern of uterine cells from birth to adulthood was investigated in mice. The uptake of 5-[125I] iodo-2'-deoxyuridine [( 125I]dUrd) by the whole uterus was used as an index of cell proliferation. Nearly parallel changes in uterine growth were found from days 0-25 after birth in both intact and neonatally castrated mice. In both groups of mice, the weight of the uterus increased (0.7-6 mg) and high [125I] IdUrd uptake values were found from days 0-15, while the weight remained nearly constant, and very low uptake values were found in the next 10 days. Additionally, we could demonstrate that adrenalectomy plus ovariectomy caused no significant effect on neonatal growth of the uterus. After day 25, the weight of uterus (6-50 mg) and [125I]IdUrd uptake increased again in the intact mice, but remained low in the neonatally castrated mice. The proliferative response of the uterine cells to exogenous 17 beta-estradiol was then examined. The injection of 17 beta-estradiol on days 0 (20 micrograms/mouse) and 10 (5 micrograms/mouse) induced significant increases in [125I]IdUrd uptake the next day. Neonatal castration had no significant effect on the responsiveness of the uterus to estrogen-induced growth in adult mice. These findings suggest that sex steroids secreted from both the ovaries and adrenals of neonatal and prepubertal mice play no significant role in the proliferation of uterine cells, and that a quiescent interval of cell proliferation occurs around day 20 after birth between the autonomous (days 0-15) and the ovary-dependent (after day 25) proliferation of mouse uterine cells.