Effect of human chorionic gonadotropin on the expression of progesterone receptors and estrogen receptors in rabbit ovarian granulosa cells and the uterus.

To investigate whether LH/human CG (hCG) or progesterone acts as a regulator of estrogen receptors (ER) and progesterone receptors (PR) in granulosa cells, we studied the immunohistochemical expression of both ER and PR in the ovary and the uterus of mature rabbits, during the induction of ovulation by FSH followed by administration of hCG, progesterone, or a progesterone antagonist (RU486) and hCG. Granulosa cells pretreated with FSH for 3 days showed ER staining, but negligible PR staining. The staining pattern for ER and PR changed in animals pretreated with FSH followed by hCG injection; by 6 h after hCG injection, we observed the disappearance of ER and the appearance of PR, and by 3 days after hCG injection, we observed the reappearance of ER and the disappearance of PR. However, the expression of ER and PR in the granulosa cells of animals pretreated with FSH followed by progesterone administration instead of hCG was almost the same as that of animals pretreated with FSH alone. In addition, the expression of ER and PR in the granulosa cells of animals pretreated with FSH followed by RU486 and hCG was almost the same as that of animals pretreated with FSH followed by hCG administration. The uterine glandular epithelium, in contrast, began to show decreased appearance of ER and PR by 48 h after hCG injection, and we observed the disappearance of both receptors by 3 days after hCG administration. These results suggest that the expression of ER and PR in granulosa cells is not regulated by the action of progesterone, but by that of LH/hCG.