Dissociation of Estradiol from a Uterine Nuclear Receptor

Dissociation of 3H-estradiol, previously bound to a uterine nuclear receptor by in vitro techniques, was enhanced when incubated with unlabeled estradiol. Other estrogens increased dissociation but testosterone produced no effect. Significant differences were noted between the association and dissociation process. Uteri containing 3H-estradiol bound to receptors in vivo were homogenized and incubated under different conditions. The distribution of radioactivityradioactivity among cellular fractions was altered. An increase in nuclear-bound material occurred during incubation at 25 or 37 C, but no change was observed at 4 C. This increase required the supernatant fraction and was specific for estradiol. Similar experiments were performed using 3H-estriol and a comparison between the 2 estrogens is made. (Endocrinology84: 718, 1969)