PRESENCE AND POSSIBLE FUNCTION OF ACTIVIN-LIKE SUBSTANCE IN HUMAN FOLLICULAR-FLUID

We assessed the presence of an activin-like substance in human follicu lar fluid that was obtained from women undergoing in-vitro fertilizati on using a bioassay for activin A. Activin activity was not detected i n crude follicular fluids; the bioactivity of standard activin A was i nhibited by the addition of follicular fluid. After the follistatin (b inding protein of activin A) was removed from follicular fluid using a purification procedure, activin activity was detected in the follicul ar fluids (mean concentration: 131 +/- 40 ng/ml). Activin activity was inhibited by the addition of follistatin to fluid. The concentration of activin activity was substantially higher (approximately 100-fold) than that reported in serum. The concentration negatively and signific antly correlated with the number of developed follicles in the ovary ( r = 0.501, P < 0.01). These results suggest that activin A and its bin ding protein are present in follicular fluid in large amounts and that they may have a role in local ovarian regulation.