Radioautographic study of the effect of estradiol-17 , estrone, estriol, progesterone, testosterone and corticosterone on the in vitro uptake of 2,4,6,7- 3 H estradiol-17 by uterine eosinophils of the rat

The in vitro uptake of 2,4,6,7-tritiated estradiol-17beta in uterine eosinophils of the rat was inhibited by the presence of nonradioactive estradiol-17beta, estrone, and estriol, but not by progesterone, testosterone, or corticosterone. This action is attributed to competition between tritiated estradiol and the various estrogenic compounds for the same binding site. Compounds without any estrogenic activity do not compete. The proposal is made that the eosinophil binding system and the 8S-5S binding system are involved in different mechanisms of estrogen action. The parallelism between the doses of estradiol and estriol needed to promote certain estrogenic early effects in the uterus, and the affinity of these steroids for the eosinophil uptake sites, suggests that uterine eosinophils might be responsible for some of these early effects, such as water imbibition, histamine releasing activity, and estrogen priming effect.