Radioautographic analysis of 6,7- 3H estradiol-17β uptake in rat uterus following extraction of endogenous estrogens

Abstract

The uptake of 6,7- 3H estradiol-17β by uterine eosinophils in the rat has been demonstrated in vitro. The number of uterine eosinophils is in direct proportion to the estrogenic level of the animal and is diminished by progesterone. Preliminary experiments in vitro have shown that the uptake capacity of each uterine eosinophil varies according to the hormonal condition of the animal, being inversely proportional to the estrogenic level in the rat. In our present research uterine sections from animals under different hormonal conditions were exposed to the action of ethanol. Ethanol partially extracts the endogenous estrogen from the intraeosinophilic acceptor sites without altering their capacity for estrogen binding. After ethanol treatment these sections were incubated in tritiated estradiol. Our aim was to find out the probable mechanism accounting for this process in eosinophils. A marked increase in estradiol uptake by eosinophils in hype r estrogenic rats ( proestrus, estrus or estrogen-treated ) was observed, whereas there was no modification in the uptake in hypoestrogenic rats ( diestrus or recently ovariectomized animals ). These results suggest that the difference in the uptake of tritiated estradiol by uterine eosinophils under different hormonal conditions are due to a competition between 6,7- 3H estradiol 17β and the endogenous estrogens for the same acceptor site. This intraeosinophilic acceptor site would have the following characteristics: a) a great affinity for estradiol-17β, b) a high specificity for molecules of estrogenic action but not for other steroid hormones, and c) a limited binding capacity for estradiol due to a finite number of these uptake sites.