Prostaglandin (PG) release from and platelet-activating factor (PAF) accumulation by enzymatically isolated endometrial epithelial and stromal cells from Day 6 pregnant and Day 6 pseudopregnant rabbits were studied in vitro, using RIA for PG measurement and a platelet aggregation assay for PAF measurement. On the first day of culture in serum-free media, PGF release into the medium was significantly higher from epithelial cells from Day 6 of pregnancy than from stromal cells from Day 6 of pregnancy or pseudopregnancy. PGE release did not differ significantly among these cell types. The addition of indomethacin (10(-5) M) to similar cultures inhibited release of both PGs from both cell types, but to a much greater extent from stromal than from epithelial cells. Significant stimulation of PG release by A23187 was achieved under all conditions on the fifth day of culture; PGE release was significantly greater than PGF release from stromal cells from Day 6 of pregnancy and pseudopregnancy, and release of both PGs from stromal cells was significantly greater from Day 6 of pregnancy than from Day 6 of pseudopregnancy. PG release from similar cells, cultured in medium containing 10% calf serum, was highest on the first or second day of culture and then, especially for PGF, declined with continued culture. PGE release was significantly higher than PGF release from stromal cells on the third and fourth days of culture. The ratios of PGF/PGE release from epithelial cells were significantly higher than those from stromal cells over the 5-day culture period for both reproductive stages. These ratios indicate the differential release of PGE and PGF from rabbit endometrial cell subpopulations and indicate a preferential release of PGE from stromal and of PGF from epithelial cells. Under basal conditions, PAF was not detected in epithelial or stromal cells cultured for 2 or 4 days, or in the associated culture media. If PAF had been released into the medium, it would have rapidly metabolized. Short exposure to calcium ionophore A23187 (10(-5) M) was able to stimulate PAF accumulation in epithelial and stromal cells in serum-free media, probably via the remodeling pathway. PAF was not detected in the medium. Intracellular PAF accumulation after exposure to A23187 (10(-5) M) for 5 min was significantly greater on the second day of culture than on the fourth day in epithelial and stromal cells from Day 6 of pregnancy. Intracellular PAF accumulation in response to stimulation with A23187 (10(-5) M) of stromal cells from Day 6 of pregnancy on the second day of culture was significantly higher than that obtained from Day 6 of pseudopregnancy, suggesting that the ability of rabbit endometrial stromal cells to synthesize PAF is increased in pregnancy. The pattern of intracellular PAF accumulation by and PG release from the same cells in response to A23187 was different. Intracellular PAF accumulation peaked 10 min after exposure to A23187 and by 30 min was declining. In contrast, PG release increased sharply 10 min after exposure to A23187 and then continued to increase up to 30 min. PAF was not detected in the majority of Day 6 blastocysts and never detected in the associated media, whether cultured or not or whether stimulated with A23187 or not. These in vitro studies show that rabbit endometrial epithelial and stromal cells exhibit differential production of PGs, existence of a pathway for PAF synthesis, and increased sensitivity to produce PAF and release PGs in pregnant animals. The close relationship between PAF and arachidonate metabolism in these cells suggests that rabbit endometrial epithelial and stromal cells can modulate their own PG and PAF production during the implantation process.
