Ovine follicular fluid inhibits aromatase activity

"Within follicle" regulations may be important for the fine tuning of gonad otrophin action in ovarian follicles. While numerous growth factors, steroi ds or proteins which are present in follicular fluid have been shown to hav e the ability of positively or negatively affecting follicle function, the net effet of follicular fluid of the dominant follicle on its function is u nclear. A bioassay measuring aromatase activity of follicular walls was used (1) to check whether follicular fluid from dominant follicles can alter aromatase activity (2), to check how follicle size, atresia and specific gonadotroph ins alter the effects of follicular fluid (3), to identify the nature (ster oid or protein) of the active compound(s), and (4) to check whether the inh ibition is specific of aromatase. Dominant follicular fluid had the ability to reduce aromatase activity. This effect was dose dependent and was obvio us whether or not a protease inhibitor was added to the incubation medium. There was no difference in the magnitude of the inhibitory effect of follic ular fluid when FSH (2 ng/ml) or no FSH was added to the incubation medium. LH, however, could potentialise the inhibitory effects of follicular fluid . Dominant follicular fluid was more potent to inhibit aromatase than folli cular fluid from atretic follicles. Medium conditioned by granulosa cells, but not by theca cells could inhibit aromatase activity when added to the i ncubation medium. Charcoal treatment of dominant follicular fluid did not r emove its inhibitory potential. Fractionation of dominant follicular fluid by a desalting column demonstrated that the inhibition was related to a com pound(s) > 10 kDa. Finally, the effect of dominant follicular fluid on arom atase appears specific of this enzyme as follicular fluid does not affect a ndrogen output by thecal shells or progesterone output by luteal cells. Further research is required to check whether the activity observed in domi nant follicular fluid is related to compounds known to affect aromatase act ivity (inhibin, mullerian inhibiting substance, heat shock protein 90, supe roxyde dismutase) or to another peptide/protein. (C) 2000 Elsevier Science Inc. All rights reserved.