Concentration of activin A and follistatin in follicular fluid from human small antral follicles associated to gene expression of the corresponding granulosa cells

The present study correlated concentrations of activin A and follistatin in follicular fluid (FF) from human small antral follicles to FF concentrations of AMH, inhibin B, progesterone, and oestradiol and to the mRNA expression of FSH-receptor (FSHR), LH-receptor (LHR), AMH-receptor2 (AMHR2), CYP19a, and androgen-receptor (AR) in the corresponding granulosa cells (GC). FF from 144 follicles (3–12 mm in diameter) was included whereas mRNA expression profiles were established in GC from 66 of the 144 follicles.Levels of follistatin remained constant in relation to follicular diameter, whereas activin A levels increased in follicles exceeding 10 mm in diameter. Levels of activin A and inhibin B showed a highly significant inverse association. Follistatin showed highly significant positive associations with AMH and inhibin B levels and with FSHR and AR gene expression in GC.This study revealed unexpected associations that probably reflect the complicated regulatory mechanisms governing human folliculogenesis.

► Levels of follistatin remained constant in relation to follicular diameter.
► The level of follistatin was ten times higher than activin in individual follicles.
► Follistatin showed highly significant positive associations with AMH and inhibin B.
► Follistatin showed significant positive association with FSHR and AR gene expression.
► Levels of activin A and inhibin B showed a highly significant inverse association.