Platelet-Activating Factor in Human Luteal Phase Endometrium1

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Abstract
Platelet-activating factor (PAF; 1-O-alkyl-2-acetyl-sn-glycero-3-phoshorylcholine) is one of the most potent mediators of vascular permeability. PAF levels change in the rabbit endometrium just prior to implantation, which suggests that PAF may be a key substance transducing preimplantation embryonic signals. To study whether PAF was present in the human endometrium, and if so, to determine the cellular origin and hormonal regulation of endometrial PAF, specimens were obtained from 14 women (aged 23-42 yr) undergoing elective hysterectomy during the luteal phase of the cycle (plasma progesterone levels > 2 ng/ml). No specimens were taken from women with malignant uterine pathology. Stromal cells and epithelial glandular cells were separated by collagenase and DNAse digestion, and then cultured to confluence in vitro in medium 199. Radioimmunoassays of prostaglandin F (PGF) and prolactin in the culture medium were used to confirm cell type and viability. PGF release into the culture medium from stromal cells was low (control 1.52 .+-. 0.20 ng/ml), and unchanged by hormone treatment. In contrast, release of PGF from unstimulated glandular cells was 6.05 .+-. 0.52 ng/ml, and was significantly increased (p < 0.05) by estradiol or progesterone plus estradiol, to 12.17 .+-. 1.67, and 8.60 .+-. 0.81, respectively. Progesterone alone was without effect. Prolactin was secreted by stromal cell cultures, increasing steadily from 24 to 120 h. The levels in the medium were increased by progesterone. PAF activity was assessed by rabbit platelet aggregation and serotonin-release bioassays after lipid extraction and separation by thin-layer chromatography. Basal PAF concentration in unstimulated stromal cells during the 24-h period after confluence was 0.14 .+-. 0.05 (mean .+-. SEM:pmol/mg protein/24 h). Progesterone combined with estradiol (10 nM) increased PAF in stromal cells in a dose-dependent manner, a 1-.mu.M dose giving the optimal response. Progesterone alone (1 .mu.M) was as effective as when combined with estradiol (10 nM) to increase PAF concentrations significantly (p < 0.05) in stromal cells, the values being 0.99 .+-. 0.15 and 1.0 .+-. 0.13, respectively. Estradiol alone had no stimulatory effect. PAF concentration in the medium was undetectable in most cultures, and did not change with treatment. PAF was not found in the glands. PAF appears to be restricted to the stromal cells of the endometrium, and its cellular concentration is increased by progesterone.

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