[Plasma estradiol concentration and uterine estrogen receptor in adult rats after steroid administration (author's transl)].

Interaction of estradiol and testosterone was studied at the level of cytoplasmic and nuclear estrogen receptors in the uterus of the adult rat. 55 Sprague-Dawley strain rats, 10 weeks old, were divided into 4 groups. Group I. 5 intact rats (proestrus). Group II. 30 rats were injected with long acting estradiol (ED: 1mg/0.2ml of estradiol dipropionate). Each 5 rats were sacrificed on day 1, 3, 5, 7, 11 and 14 days respectively after the ED injection. Group III. 10 rats were injected with ED. Vehicle (0.2ml of dimethyl sulfoxide) and 1mg/ 0.2ml of testosterone were injected from the 3rd day of the ED injection for 5 days into each 5 rats respectively. Group IV. 10 rats were injected with ED. The rats were treated similarly to Group III except that vehicle or testosterone injections began from the 7th day. Plasma estradiol was determined by RIA. The DCC method for cytoplasmic receptor assay and the pellet exchange method for nuclear receptor assay were used. As to unbound receptor assay, the material was incubated with tritiated estradiol at 0 degrees C for 2 hours. Incubation at 30 degrees C for 1 hour was added to the above for bound receptor assay. Plasma estradiol levels increased 1 day after the ED injection and remained very high for 7 days and decreased to five times that of intact rats 14 days after the injection. Plasma estradiol levels were not influenced by injections of vehicle or testosterone. In group II, cytoplasmic estrogen receptor decreased 1 day after the ED injection and remained low for 7 days and then returned gradually. In nucleus bound receptor increased. Fluctuation of estrogen receptors in uterine cytoplasma and nucleus was in accordance with the concentration of plasma estradiol. In Groups III and IV, there was no significant difference in cytoplasmic and nuclear estrogen receptors between vehicle and testosterone injections. Plasma estradiol levels and uterine cytoplasmic and nuclear estrogen receptors of the ED-treated rats were not influenced by testosterone injections. It is supposed that interaction of estradiol and testosterone may occur in the protein or DNA synthesis mechanism after the receptor level.