Variations of prostaglandin E2 receptors in hamster's ovary and endometrium during estrous cycle

The purpose of this study was to determine concurrent ovarian and endometrial prostaglandin E2 (PGE2) receptor concentrations throughout the hamster estrous cycle. The effect of progesterone (P4) on PGE2 receptor in these two tissues was also investigated during in vitro culture. Estrous cycles of mature female hamsters were monitored according to the appearance of the vaginal discharge on cycle day 1 (D1). Ovaries and uteri were removed from cyclic hamsters at 10:00 a.m. on each day of the cycle and at 6:00 p.m. on D4 (proestrus). Ovarian and endometrial cell membranes were collected and assayed for the specific PGE2 binding by Scatchard plot analysis, using seven different concentrations of 3H-PGE2 (0.72-9.1 nM) with or without the presence of unlabelled PGE2 (9.1 microM). Ovarian and endometrial tissues of the cyclic hamsters were shown to contain a saturable, specific binding site with KD=4.69+/-0.55, and 5.7+/-0.4 nM for ovary and endometrium, respectively. Relative binding activity of PGE1 for the PGE2 binding site was about 28%. PGF2alpha and PGA1 did not compete for the PGE2 binding site. In ovaries, the PGE2 receptor levels started to increase sharply in the evening of D4 and reached maximum in the morning of D1. A precipitous drop of PGE2 receptor was observed on D2 followed by gradual decreases on D3 and D4. The PGE2 receptor concentrations in endometrium were the lowest in the morning of D4, and increased thereafter until a maximal level was reached on D2. Progesterone (10 nM) augmented PGE2 receptors in ovarian but not in endometrial tissue during 24-h in vitro incubation.