Alpha-fetoprotein serum levels and the development of estrogen-sensitive cell multiplication in the hamster uterus.

Subcutaneous injections of 5 or 25 micrograms estradiol-17 beta (E2)/kg in ovariectomized adult hamsters produced substantial increases in uterine wet weight, protein content and the mitotic indices of the glandular and luminal epithelia. However, no significant increase was seen in total uterine DNA. Intact hamsters from 2 to 25 days of age received a daily subcutaneous injection of 5 micrograms E2/kg for 2 consecutive days. Significant increases in uterine wet weight and protein content first occurred at 8 and 17 days, respectively. No significant increase was observed in uterine DNA. In a separate experiment, hamsters between 2 and 20 days of age received one subcutaneous injection of 5 micrograms E2/kg. Mitotic indices in the stroma were increased at 6 and 10 days of age. Mitotic indices in the luminal epithelium were significantly increased only at 6 days of age. Rocket immunoelectrophoresis revealed a sharp decline in serum alpha-fetoprotein (AFP) concentrations after 2 days of age. Estradiol concentrations in the sera of immature hamsters gradually decreased from 55 pg/ml at 0 days of age to 17 pg/ml at 20 days of age. These results provide a quantitative analysis of the effects of E2 upon cell proliferation in the hamster uterus. The correlation of declining AFP levels and the incipience of the mitotic response to estrogen suggests that AFP may directly inhibit estrogen-sensitive cell multiplication in the neonate. Other possible causes for the lack of a mitotic response in the uterus of the newborn hamster to the administration of E2 are also discussed.