Activin and follistatin in female reproduction.
Muttukrishna S., Tannetta D., Groome N., Sargent I.
Activin and follistatin were initially identified in the follicular fluid based on their effects on pituitary FSH secretion in the mid-1980s. It is now evident that activin, follistatin and activin receptors are widely expressed in many tissues where they function as autocrine/paracrine regulators of a variety of physiological processes including reproduction. The major function of follistatin is to bind to activin with high affinity and block activin binding to its receptors. Total activin A and follistatin are also found in the maternal circulation throughout pregnancy. Activin A levels are increased in abnormal pregnancies such as pre-eclampsia, fetal growth restriction and gestational hypertension. The placenta, vascular endothelial cells and activated peripheral mononuclear cells (PBMC) may all contribute to the raised levels of activin A in pre-eclampsia with unaltered follistatin in pre-eclamptic placenta, PBMCs or vascular endothelial cells suggesting the availability of 'free' activin A that could be biologically active in these cells.