The amnion produces little of the prostaglandin E2 detected on the decidual side of human fetal membranes.

Cultured intact fetal membrane disks initially produced high levels of prostaglandin E2 (PGE2) on the fetal and maternal sides which declined during four days of culture. The transfer of a bolus of PGE2 from the fetal side to the maternal side of the membrane ranged from 1% to 3% after 24 hours of culture, and was a minimum over the period of 48-72 hours from the start of the incubation. To assess the handling of PGE2 synthesized by the amnion, 3H-arachidonic acid was incorporated into cultured amnion and into the amnion side of cultured intact fetal membrane disks. Labelled amnion released 3H-PGE2 on both sides of the tissue, whereas similarly labelled cultured intact fetal membrane only had detectable levels of 3H-PGE2 on the fetal side. It was calculated that no more than 9.7 +/- 1.4% of the PGE2 synthesised by the amnion crossed to the maternal side of the membrane without being metabolised during the transfer through the membrane. These results are consistent with similar indirect methods which suggested that PGE2 from the amnion may have only a limited role in human labor, and indicates the importance of using appropriate culture systems to investigate intra-uterine prostaglandin production.

Metabolism of prostaglandins E2 and F2 alpha by human fetal membranes.

Prostaglandin E2 (PGE2) is important in the early stages of human labour, leading particularly to cervical ripening and dilatation. The source of PGE2 is thought to be either the amnion or the decidua, but the chorion interposes between the amnion and the target tissues, namely the myometrium and cervix. In order to investigate the role of the chorion in modulating prostanoid production, [3H]PGE2 was added to the amnion side of fetal membranes, and the production of metabolites on both sides of the fetal membrane followed by HPLC. The major metabolite was 13,14-dihydro-15-oxo-PGE2 with smaller amounts of 13,14-dihydro-15-oxo-PGA2 and PGB2. The production of all metabolites of PGE2 was time dependent. [3H]PGF2 alpha, which is normally produced by the decidua, was also added to fetal membranes and found to be metabolised to 13,14-dihydro-15-oxo-PGF2 alpha and PGE2. These results suggest that the metabolic enzymes in the chorion may determine intra-uterine levels of prostaglandins, and may also determine the identity of the eicosanoids released by intact fetal membranes.

Quantitative production of prostaglandin E2 and its metabolites by human fetal membranes.

Cultured amnion, choriodecidua and intact fetal membrane produced similar quantities of prostaglandin E2 (PGE2) (1-5 ng/ml). Choriodecidua and intact fetal membrane also produced very high levels of PGE2 metabolites (100-1000 ng/ml). The total production of PGE (PGE2 + PGE2 metabolites) was similar in intact fetal membrane and in choriodecidua, suggesting that the amnion, although a source of PGE2, contributes little to the overall PGE production by fetal membranes.

Metabolism of prostaglandin E2 on the fetal and maternal sides of intact fetal membranes.

The metabolism of prostaglandin E2 (PGE2) added to the chorio-decidual side or the amnion side of the intact fetal membrane was compared. Similar rates of metabolism were found when the PGE2 was added to the fetal side or the maternal side of the membrane, even though the amnion (on the fetal side of the membrane) contains no metabolizing enzymes. The appearance of PGE2 metabolites on the opposing side of the membrane was also independent of whether the PGE2 was added to the fetal or maternal side, which suggests that the chorion, which lies between the amnion and the decidua, is the major determinant of the rate of metabolism of PGE2. Furthermore, it might be expected that less PGE2 metabolism subsequent to diffusion across the membrane may occur on the amnion side, since this tissue contains no metabolizing enzymes, but no evidence for this was found. PGE2 synthesized by the amnion would therefore have little effect on PGE2 levels on the maternal side of the fetal membrane, and may not be directly involved in labour.

Use of a new simplified assay for phospholipase A2 to measure bacterial enzyme levels.

During investigation of possible phospholipase A2 (PLA2) production by pathogenic bacteria associated with preterm labour, a rapid and simple assay method was developed which involved few steps and which could be applied easily to large numbers of samples. The principle difference from previously described methods lies in separation of the reaction products by partitioning them between organic and aqueous solvents, rather than by using thin layer chromatography. This enabled us to determine that none of the bacteria studied released PLA2 into the culture medium spontaneously, and that only Escherichia coli contained high levels of PLA2.

Control of fetal membrane prostaglandin E2 production by bacteria.

The effect of bacteria on the production of prostaglandin E2 (PGE2) and PGE2 metabolites by fetal membranes has been investigated. Live bacteria stimulated a large increase in the levels of PGE2 metabolites, but only a small increase in the levels of PGE2 on the fetal side of the membranes. No significant changes in the levels of PGE2 or its metabolites were found on the maternal side. Bacteria may therefore stimulate PGE2 production by fetal membranes during short-term incubations, but it seems that the metabolic capacity of the chorion was so high that no change in PGE2 levels was detectable on the maternal side of the fetal membranes. This was confirmed by the finding that less than 1% of 3H-PGE2 added to the fetal side of the membrane reached the maternal side without being metabolized.

Limited transfer of prostaglandin E2 across the fetal membrane before and after labor.

The transfer of prostaglandin E2 (PGE2) across intact fetal membranes (amnion-chorion-decidua) obtained before and after the onset of labor was investigated using a novel system for in vitro fetal membrane culture. Studies using physiological concentrations of PGE2 showed that very little PGE2 will cross the membranes without being metabolised, before or after the onset of labor. It was only when pharmacological concentrations of PGE2 were used that the enzyme activity of the chorion was no longer able to prevent transfer of PGE2 without conversion to inactive metabolites. These results suggest that only small amounts of PGE2 from amnion are normally transferred across the chorio-decidua before or after the onset of labor, but the metabolism of PGE2 subsequent to transfer across the fetal membranes requires further assessment.