Ovary: Follistatin concentrations in follicular fluid of normal and polycystic ovaries

Follistatin (FS) is an activin/inhibin binding protein whichis believed to act in an autocrine/paracrine manner to regulategrowth and differentiation. Although FS has been identifiedin human follicular fluid, it remains unclear how its concentrationchanges during selection and atresia, and what the concentrationsof FS are in follicles of women with polycystic ovary syndrome(PCOS). Towards this goal, we have measured by radioimmunoassaythe concentrations of FS in follicular fluid obtained from dominantand atretic cohort follicles of normal cycling women, preovulatoryfollicles of in-vitro fertilization (IVF) patients, and smallGraafian follicles of patients with PCOS. In all cases, thefollicular fluid concentration of FS was much higher (100-fold)than that reported in serum. The FS concentrations (ng/ml) were203 ± 42 (normal dominant), 185 ± 17 (atreticcohort), 185 ± 5 (IVF), and 250 ± 14 (PCOS). Therewas no statistical difference between these mean values of FS.Further, there were no significant correlations between thefollicular fluid concentrations of FS and the concentrationsof oestradiol, progesterone, or androstenedione. These resultsindicate that human Graafian follicles, regardless of whetherthey are healthy or atretic, normal or PCOS, contain high steady-stateconcentrations of FS in the micro-environment. Collectively,these data fit with the hypothesis that major increases anddecreases in the concentration of FS in the micro-environmentmay not play a key role in the mechanisms of selection, atresia,and PCOS in women. The possibility of regulation of intrinsicactivin and inhibin activity through FS binding is discussed.