EFFECTS OF RECOMBINANT ACTIVIN-A ON IN-VITRO CULTURE OF MOUSE PREANTRAL FOLLICLES

Activins are part of the intragonadal factors that can modulate the ac tions of gonadotropins and regulate cellular functions during preantra l or early antral stages of folliculogenesis in vivo. In a mouse early preantral follicle culture system, activin A production was measured and recombinant bovine activin A (r-ACT A) was added (10 or 50 ng/ml) to recombinant follicle-stimulating hormone (r-FSH)-supplemented (10 o r 100 mIU/ml) medium for a 12-day culture period. Specificity of activ in A action was ascertained by addition of recombinant human follistat in (r-FS; 20 or 100 ng/ml). Immunoreactive activin A concentrations in mouse follicle-conditioned medium increased by a factor of 20-50, rea ching concentrations from 2 to 5 ng/ml at end of culture. In the initi al days of culture, additions of r-ACT A to r-FSH-supplemented medium provoked a dramatic volumetric increase and earlier attachment of the follicle. A dose of 100 ng/ml r-FS was able to block the actions of 10 ng/ml but not those caused by 50 ng/ml r-ACT A. In follicle cultures supplemented with 10 mIU/ml r-FSH, additions of r-ACT induced a dose-d ependent inhibin (INH) and estradiol (E-2) increase. Basal and human c horionic gonadotropin (HCG)-induced progesterone (P) production were n ot influenced by r-ACT A or r-FS additions. Addition of r-ACT A decrea sed (P = 0.017) the intact follicle survival rate and had no influence on final oocyte diameter. In cultures supplemented by 10 mIU/ml r-FSH , additions of r-ACT A did not influence progression and resumption of meiosis I. Use of a higher r-FSH supplementation dose (100 mlU/ml) te nded to affect meiosis I adversely (P = 0.052), and r-ACT A addition a mplified this effect significantly (P = 0.007). These in vitro experim ents demonstrate pronounced effects from r-ACT on r-FSH-mediated folli cle survival, growth, and estrogen biosynthesis. (C) 1998 Wiley-Liss, Inc.