Effect of mifepristone (RU 486) on concentrations of prostaglandin E-2 binding sites in the rat endometrium

Human granulosa-lutein cells express functional EP1 and EP2 prostaglandin receptors

Prostaglandin E(2) (PGE(2)) exerts mainly luteotrophic effects in the corpus luteum. In other tissues, PGE(2) acts via specific PGE(2) receptor subtypes including EP1, which modulates intracellular calcium ([Ca(2+)](i)) and EP2, which is coupled to cyclic AMP (cAMP) generation. We have therefore investigated the presence of functional EP1 and EP2 receptors using human granulosa-lutein (GL) cells. Reverse-transcription PCR revealed that GL cells expressed mRNA transcripts encoding both EP1 and EP2 receptors. When GL cells were challenged with ligands that can bind to both receptor subtypes (PGE(2) and 16,16 dimethyl PGE(2)) or exclusively to EP2 (butaprost), both cAMP formation and progesterone synthesis were stimulated. Furthermore, the cAMP response to these agonists could be significantly blocked by an EP1/2 antagonist AH6809 but not by an EP1-selective antagonist SC19220. Exposure of GL cells to 16,16-dm PGE(2) transiently raised [Ca(2+)](i) levels, which could be prevented by both AH6809 and SC19220. We therefore conclude that human GL cells express functional EP1 and EP2 receptors.

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.

Deciduogenic effects of mediators of the polyphosphatidylinositol pathway in pseudopregnant mice

Intraluminal injections (15 microliters) of either concanavalin A (125 micrograms) or ionophore A 23,187 (0.01 mumol) induced a decidual cell reaction (DCR) in the uterus of day 4.5 pseudopregnant mice. However, when these agents were administered in different combinations with each other or with CaCl2 (15 mumol) and phorbol-12-myristate-13-acetate (1.6 nmol), interacting effects occurred to either enhance or inhibit each of the others' independent deciduogenic capacities. The results suggest that the polyphosphatidylinositol pathway and Ca2+ are involved in the induction of the DCR in mice with complex interactions occurring between the active components of the pathway to modulate the outcome of the transformation process.

Low dose RU486 prevents progesterone antagonism on uterine growth and concomitant type II oestradiol binding induction by oestradiol in rats

The effect of RU486, a synthetic antisteroid, on the antagonism of progesterone (Pg) and dexamethasone (Dex) against oestradiol (Oe) induced uterine growth, and on uterine oestradiol binding (type I and type II sites) was studied in ovariectomized CFY rats. Changes of hypothalamic low affinity [3H]Oe binding have also been evaluated. Inhibitory effects of Pg but not of Dex on uterine growth and type II Oe binding site induction were prevented by RU486. Antiprogestin effect of RU486 could also be demonstrated on low affinity [3H]Oe binding in hypothalami. The inhibitory effect of dexamethasone on type II Oe binding was not opposed by antisteroid, on the contrary, RU486 seemed to potentiate this effect of Dex. Evaluation of type I binding was complicated by the distorting effect of type II binding at the saturation curve. Changes of type I binding seemed to parallel those of type II binding except after Oe+Dex treatment where an increased level of uterine cytoplasmic type I sites and a simultaneous decrease of type II sites were found. Blockage of [3H]Oe binding at high RU486 concentrations was found in vitro in the uterine cytoplasmic fraction. A less pronounced effect was observed in the nuclear fraction. Possible mechanisms of the RU486 effect on type II Oe binding are discussed.