Activin at parturition: changes of maternal serum levels and evidence for binding sites in placenta and fetal membranes

OBJECTIVE: To evaluate maternal serum activin A levels in pregnant women at parturition, correlated to the mode of delivery, and to localize activin receptor messenger RNA in human placenta and fetal membranes. METHODS: A specific two-site enzyme-linked immunosorbent assay (ELISA) was used to measure maternal activin A levels. Activin receptor mRNA was localized in placenta and fetal membranes by in situ hybridization, using ActRII or ActRIIB antisense riboprobes. RESULTS: Serum activin A levels increased significantly in pregnant women during vaginal or cesarean delivery after spontaneous labor. No significant changes of serum activin A were found in patients undergoing elective cesarean delivery. Syncytiotrophoblast and amnion cells hybridized to radiolabeled ActRIIB probe, whereas few cells within the structure of the villi and decidual cells hybridized to radiolabeled ActRII probe. CONCLUSION: The present studies indicate that vaginal or cesarean delivery following spontaneous labor is characterized by increased activin A levels and that activin receptors are present on trophoblast and fetal membranes.