Interactions Between Follicle-Stimulating Hormone and Growth Factors in Modulating Secretion of Steroids and Inhibin-Related Peptides by Nonluteinized Bovine Granulosa Cells1

Abstract

The aim was to investigate potential interactions between FSH and intraovarian growth factors in modulating secretion of inhibin A (inh A), activin A (act A), follistatin (FS), estradiol (E2), and progesterone (P4) by bovine granulosa cells cultured under conditions in which a nonluteinized FSH-responsive phenotype is maintained. Cells from 4- to 6-mm follicles were cultured in serum-free medium containing insulin (10 ng/ml) and androstenedione (10(-7) M), and effects of ovine FSH (0.037-3 ng/ml) were tested alone and in combination with insulin-like growth factors (IGF) (LR3 IGF-I analogue; 2-50 ng/ml) and epidermal growth factor (EGF; 0.1-10 ng/ml). Medium was changed every 48 h and cultures ended after 144 h, when cell number was determined. Between 48-96 h and 96-144 h, FSH promoted (P < 0.0001) increases in output of inh A (6-fold), act A (15-fold), FS (6-fold), and E2 (18-fold), with maximal responses (in parentheses) elicited by 0.33 ng/ml FSH during the final period. Higher FSH doses (1 and 3 ng/ml) gave reduced responses for each of the above hormones, whereas P(4) output was maximal (3-fold) at these doses. FSH promoted a slight increase in cell number ( approximately 1.7-fold; P < 0.001). LR3 IGF-I alone markedly increased (P < 0.0001) output of inh A (8-fold), act A (41-fold), FS (12-fold), and E2 (18-fold); this was accompanied by modest increases (P < 0.01) in P4 output ( approximately 2.5-fold) and cell number ( approximately 2-fold). Whereas FSH enhanced inh A, act A, FS, and E2 secretion evoked by lower doses of LR3 IGF-I, it suppressed (P < 0.001) the response to the highest dose. EGF alone promoted a 1.7-fold increase in cell number (P < 0.001) without affecting hormone release; however, it abolished (P < 0.001) FSH-induced secretion of inh A, act A, FS, and E2. Both FSH alone and LR3 IGF-I alone dose-dependently increased the act A:FS ratio ( approximately 3-fold; P < 0.005) and act A:inh A ratio (3-fold to 6-fold; P < 0.001), suggesting that both factors selectively raise activin "tone" and that this could be a key requirement for FSH and IGF-induction of follicular E2 production. This hypothesis was reinforced by the finding that addition of FS, to reduce the act A:FS ratio and sequester secreted activin, markedly suppressed (P < 0.001) FSH (3-fold)-, and LR3 IGF-I (2-fold)-induced E2 output.

Ovarian follicle development in the laying hen is accompanied by divergent changes in inhibin A, inhibin B, activin A and follistatin production in granulosa and theca layers

“…It seems likely that the intrafollicular balance between inhibin, activin and its binding protein FS is important in determining follicular response to these proteins (Findlay et al 2001, Knight & Glister 2001. However, while the present study has clearly shown that such changes occur, it is not possible to assess whether these merely reflect, rather than contribute to, the process(es) which drive follicles through specific developmental checkpoints during folliculogenesis.…”

“…) are present in the ovaries of most mammalian species examined (Knight & Glister 2001). mRNAs encoding inhibin/activin -, A-and B-subunits are also detectable in chicken ovarian follicles (Chen & Johnson 1996, Davis & Johnson 1998 and increasing evidence suggests inhibin-related proteins have important roles in regulating ovarian function in birds.…”

“…Within-and between-plate coefficients of variation (CV) were <10% for each assay. Concentrations of P4 (Sauer et al 1986), A4 (Wrathall & Knight 1995) and E2 (Glister et al 2001) were determined by competitive immunoassay as previously described. Within-and between-assay CV values for steroid assays were all <10%.…”

Follicle-stimulating hormone isoforms and plasma concentrations of estradiol and inhibin A in dairy cows with ovulatory and non-ovulatory follicles during the first postpartum follicle wave

“…Granulosa cell secretion of dimeric inhibin A is regulated by FSH (21,22), and increases as the dominant follicle approaches 185 preovulatory status (17,23). In the current study, cows with ovulatory follicles had higher circulating inhibin A compared to cows with non-ovulatory follicles, despite having lower circulating FSH concentrations.…”

Selected molecular and physiological aspects of mammalian ovarian granulosa cells in primary culture

“…IGF-I also increases expression of LH receptors and responsiveness to FSH, which is reported to enhance aromatase production in the in vitro culture of mouse, sheep, and pig GCs (1,37,39). IGF-I has also been reported to increase the expression of estradiol in GCs (14). Conversely, in 2000 Khalid et al discovered that estradiol or FSH stimulate synthesis of IGF-I (27).…”