PARENT SESSION
Follicular Development
107
INHIBIN SUPPRESSES ESTRADIOL PRODUCTION BY BOVINE GRANULOSA CELLS ISOLATED FROM FIRST WAVE DOMINANT FOLLICLES.
Jimenez-Krassel, Fermin1, Knight, Phil2, Austin, Edward3, Roche, James3,4, Ireland, James1, 1 2 3 4
ABSTRACT- Intrafollicular concentrations of estradiol (E) and inhibin-A (INH) vary inversely during growth of first-wave dominant follicles in cattle. Thus, INH may suppress capacity of dominant follicles to produce E. To test this hypothesis, ovaries were obtained at an abattoir from cows between days 2 to 10 of an estrous cycle, which is during growth of the first wave dominant follicle. Granulosa cells were isolated from estrogen-active [EA, E > progesterone (P) in follicular fluid] or estrogen-inactive (EI, P > E) dominant follicles and cultured (100, 000 cells/well in triplicate) in serum-free Hams F12 media for 16 h. Granulosa cells from an EI dominant follicle were untreated, or treated at t = 0 h with 1 ug of affinity-purified bovine INH or BSA. Concentrations of E in media were determined at 16 h. INH reduced (P < 0.05) E production 75% compared with untreated or BSA-treated controls. Immunoblots of media showed that INH was produced by granulosa cells during culture. Our next study tested whether INH produced during culture altered capacity of granulosal cells to produce E. Granulosa cells were from EA (n = 15 follicles) or EI (n = 32) dominant follicles. Pools of cells from each follicle were treated at t = 0 h with 1 mg purified bovine immunoglobulins (IgG, control) or bovine anti-INH antibodies. Basal E was 4-fold higher (P < 0.05) for granulosa cells from EA vs EI dominant follicles. However, anti-INH antibodies increased (P < 0.05) basal capacity of granulosa cells from EA or EI dominant follicles to produce E 6- or 12-fold, respectively, compared with controls. In the last study, the effect of various doses of anti-INH antibodies or IgG on E production by granulosa cells from EA (n = 2) or EI (n = 1) dominant follicles were tested. INH antibodies increased E production by granulosa cells from EA and EI follicles in a dose dependent fashion (P<0.01) compared with controls, but responsiveness of granulosa cells to INH antibodies was 3-fold greater in cells from EI vs EA follicles. We concluded that INH may have a negative autocrine or paracrine role in regulation of E production by granulosa cells during growth of the first wave dominant follicle in cows. Supported by USDA 1999-02241 to JJI.
KEY WORDS: Dominant non-ovulatory follicle, Inhibin, Estradiol