Steroid hormone receptors in the uterus and ovary of immature rats treated with gonadotropins

We administered either saline (group A) or 10 IU of pregnant mare serum gonadotropin (PMS; groups B and C) to female immature rats. Fifty-three hours later, the rats were injected with saline (groups A and B) or 30 IU of human chorionic gonadotropin (hCG; group C). The rats were decapitated 17 h after the last treatment, and the serum levels of progesterone (P4) and estradiol (E2) were measured by specific radioimmunoassays (RIA). The receptor levels of progesterone (PR) and estrogen (ER) in the uterus and ovaries were measured and the dissociation constant (Kd) of PR was obtained. The highest serum level of P4 was found in group C and that of E2 in group B. Cytosol levels of PR and ER in the uterus and ovary of the group B were the highest. It was indicated that the PMS treated-group (B), which had developing follicles in the ovary and the high serum level of E2, showed the highest concentration of ER and PR in both the ovary and the uterus. In the PMS and hCG-treated group (C), the uterine and ovarian steroid receptors decreased probably because of the luteinization and the high serum level of P4. The Kd uterine PR value was less than that of ovarian PR.