Follistatin and activin A in extra-embryonic coelomic and amniotic fluids and maternal serum in early pregnancy

Follistatin is a specific binding protein which controls bioavailability ofactivins and inhibins which have an important role in fetal development. Inthe first trimester of pregnancy bioactive dimeric inhibins are found athigh concentrations in the extra- embryonic coelomic fluid, but thedistribution of follistatin and activins is not known. We have usedrecently developed immunoassays for follistatin, activin A and activin ABto determine their presence in the intrauterine compartments during earlypregnancy. Follistatin was present in highest concentrations in theextra-embryonic coelomic fluid (11.72 +/- 1.70 ng/ml; median +/- SEM), withless in maternal serum (6.35 +/- 4.58) and lowest amounts in amniotic fluid(0.97 +/- 0.52). Follistatin concentrations in extra-embryonic coelomicfluid were highly correlated with both dimeric inhibin isoforms. Activin Awas present in only barely detectable amounts in some samples of extra-embryonic coelomic fluid (41% of samples) and maternal serum (26%) and wasundetectable in all amniotic fluid samples. Activin AB was undetectable inall compartments. The presence of follistatin in the amniotic andextra-embryonic coelomic fluids may regulate the availability of bioactiveactivins and inhibins which are released into the intrauterine compartmentsduring the development of the fetus and placenta in early pregnancy.