The dynamics of prostaglandin metabolism in human fetal membranes and decidua around the time of parturition.

To address whether prostaglandins (PGs) produced in the amnion can gain access to the myometrium, we used three in vitro systems to determine the characteristics of PG secretion, metabolism, and transfer in amnion, chorion, and decidua around the time of parturition. PG metabolism, measured in explant cultures or cytosol preparations, occurs predominantly by the enzyme PG dehydrogenase, which was highest in chorion and was 2- to 3-fold more active for PGE2 than PGF2 alpha. The activity increased significantly around the time of labor onset. The activity of PG-9-ketoreductase, which interconverts the E and F series of PGs, was 2-3 orders of magnitude less than that of PG dehydrogenase. Using a dual chamber perfusion apparatus, we demonstrated that similar amounts of PGE2 were secreted from the fetal (amnion) and maternal (chorio-decidua) surfaces, and this ratio did not change with labor. Using radiolabeled PGE2, radioactivity traversed full thickness membranes at the rate of 4%/h. Only approximately 12% of the transferred radioactivity remained as intact PGE2, and very little conversion to PGF2 alpha was detected. No changes in transfer were detected around the onset of labor. We conclude that it is unlikely that PGE2 produced in the amnion acts directly on the myometrium.