[Selection of preparations with anticipated antiestrogen activity]

Specificity of interaction between estrogen-receptor systems of guinea pig uterus and oviducts and six estrogens was studied. The obtained datas suggest existence of tissue specificity in estrogen-receptor interaction in uterus and oviducts. Modifications of the steroid molecule led to decrease in extent of estrogen affinity. Introduction of an ethyl group into 17 alpha-position resulted in the effect, by the rate of estrogen-receptor binding equal to reduction of 17 beta-hydroxyl. Low but distinct affinity of 17 alpha-estradiol, its structure and stability, enabled to select this substance as a preparation with anticipated anti-estrogenic activity.