Production of inhibin forms by the fetal membranes, decidua, placenta and fetus at parturition

Inhibins are regulators of paracrine and endocrine function during pregnanc y, but their intrauterine sites of secretion are not well established. In a mniotic fluid, inhibin A-, inhibin B- and inhibin pro-alpha C-containing is oforms were present in high concentrations, whereas in maternal serum, inhi bin A and pro-alpha C forms were present in high amounts, with low concentr ations of inhibin B. In fetal cord serum, inhibin pro-alpha C was present i n all samples, inhibin B was detectable in male but not female fetuses, wit h no detectable inhibin A in either sex. From cultured explants, both inhib in A and B were secreted by chorion laeve, whereas only inhibin A was secre ted by placenta, with both tissues secreting inhibin pro-alpha C, Only low concentrations of both dimeric inhibins and pro-alpha C forms were secreted by decidua parietalis and amnion, The dual perfused placental cotyledon se creted both inhibin A and pro-alpha C into maternal perfusate, but only inh ibin pro-aC into the fetal circulation and less than to the maternal side. We conclude that trophoblast is the predominant source of dimeric inhibins, but with markedly different secretion depending on its intrauterine locati on, There was a significant decrease in inhibin A and pro-alpha C in amniot ic fluid collected at term active labour compared to elective Caesarean sec tion (P < 0.001). This may reflect a local change in inhibin/activin proces sing at labour likely in chorion laeve trophoblast cells, which may be impo rtant in the paracrine control of the feto-maternal communication required to maintain pregnancy and initiate labour.