Endometrial prostaglandin E2 binding during the estrous cycle and its hormonal control in ovariectomized rats

Binding of [3H] prostaglandin E2 ([3H]PGE2) to endometrial membrane preparations obtained from rats at known stages of the estrous cycle and from ovariectomized rats treated with various combinations of progesterone and estradiol was determined. No specific, high-affinity binding of [3H]PGE2 could be detected by endometrial membrane preparations obtained throughout the estrous cycle. In ovariectomized rats treated with progesterone and estradiol to induce either the neutral, receptive or postreceptive phase of the endometrium for blastocyst implantation, the greatest concentration of endometrial PGE binding sites was found in the preparations from the neutral phase. Treatment of ovariectomized animals with estradiol and progesterone, alone or combined, revealed that endometrial PGE binding sites were progesterone-dependent, and were first detectable 48 h after the initiation of progesterone treatment. Following separation of the endometrial luminal epithelium and stroma in progesterone-treated ovariectomized rats, PGE binding sites were detected only in the stromal membrane preparation. The results indicate the endometrial PGE binding sites in the rat are under hormonal control and that no simple relationship exists between the concentration of endometrial binding sites and uterine sensitization for the decidual cell reaction.