[Characteristics of the estrogen receptor system of the guinea pig uterus].

Physico-chemical parameters of estradiol-receptor interaction in guinea pig uterine cytosol (velocity constants of association and dissociation, half-life time of estradiol-receptor complex, and the value of free energy change) were studied. The number of receptor sites per cell was calculated. It was shown that under conditions of different degree of approximation to the equilibrium, the affinity percentage in the system under study remained unchanged for the majority of steroids, this pointing to the achievement of equilibrium in these cases. The steroid affinity to the analyzed R-system depended on presence of intact 3- and 17beta-hydroxils with somewhat greater significance of 3-(phenolic) hydroxil of steroid molecule.