Autoradiographic studies on the fetal and newborn uteri of the guinea pig after injection of 3H-progesterone into non-treated and into estradiol-primed animals.

The localization and retention of radioactivity in the uteri of fetal and newborn guinea pigs was studied after subcutaneous injection of 3H-progesterone into intact and estradiol-primed animals. In the fetal uterus of the animals treated with estradiol, a significant increase in the accumulation of silver grains was observed, mainly localized in the stroma and myometrium, but very little is detected in the uterine gland. On the other hand, in the uteri of newborns, the effect of estradiol on radioactivity retention was significantly less intense and the radioactivity is mainly localized in the epithelium and the uterine gland. These data correlate well with the quantitative evaluation of the concentration of progesterone-specific-binding sites in the non-treated and in the estradiol-primed fetal and newborn guinea pigs.