title: Effect of follicle size on in vitro production of steroids and insulin-like growth factor (IGF)-I, IGF-II, and the IGF-binding proteins by equine ovarian granulosa cells.
abstract: Little is known regarding the hormonal regulation of granulosa cell steroidogenesis and the ovarian insulin-like growth factor (IGF) system in the mare. The objectives of this study were to determine, first, if estradiol, insulin, and/or FSH affect steroid production by equine granulosa cells (experiment 1) and, second, if the components of the IGF system are produced by equine granulosa cells in culture as well as whether estradiol, insulin, and/or FSH affects IGF and/or IGF-binding protein (IGFBP) production by equine granulosa cells (experiment 2). Granulosa cells from small (6-15 mm), medium (16-25 mm), and large (25-48 mm) follicles were collected from cyclic mares (n = 14), cultured for 2 days in medium containing 10% fetal calf serum, washed, and then treated for an additional 2 days in serum-free medium with or without added hormones. In experiment 1, large-follicle granulosa cells produced less progesterone and more estradiol than did medium- and/or small-follicle granulosa cells (P < 0.05). Progesterone production was inhibited (P < 0.05) by FSH and insulin in small- and medium- but not in large-follicle granulosa cells; estradiol was without effect. Insulin increased (P < 0.05) estradiol production in small- and medium-follicle granulosa cells but had no effect in large-follicle granulosa cells. In experiment 2, IGF-I production was inhibited (P < 0.05) by insulin across all follicle sizes but was not affected by estradiol or FSH. Granulosa cells of medium and large follicles produced more IGF-II than did granulosa cells of small follicles (P < 0.05). Insulin and FSH inhibited (P < 0.05) IGF-II production by granulosa cells of large and medium but not of small follicles; estradiol was without effect. Only IGFBP-2 and -5 were produced by equine granulosa cells. Production of IGFBP-2 was less (P < 0.10) in granulosa cells of large versus those of small and medium follicles, whereas medium-follicle granulosa cells produced more (P < 0.05) IGFBP-5 than did small- or large-follicle granulosa cells. Averaged across follicle sizes, estradiol increased (P < 0.05) IGFBP-2 production, FSH increased (P < 0.10) IGFBP-2 and -5 production, and insulin was without effect. These results indicate that IGF-I, IGF-II, IGFBP-2, and IGFBP-5 are produced by equine granulosa cells and that insulin, FSH, and estradiol play a role in the regulation of steroidogenesis and the IGF system of equine granulosa cells.
authors.affiliation: Department of Animal Science, Oklahoma State University, Stillwater, Oklahoma 74078, USA.
authors.forename: Tonya R
authors.initials: TR
authors.lastname: Davidson
authors.forename: Connie S
authors.initials: CS
authors.lastname: Chamberlain
authors.forename: Tamara S
authors.initials: TS
authors.lastname: Bridges
authors.forename: Leon J
authors.initials: LJ
authors.lastname: Spicer
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D003470:Culture Media; D016895:Culture Media, Serum-Free; D004958:Estradiol / Q000096:biosynthesis / Q000494:pharmacology; D005260:Female; D005640:Follicle Stimulating Hormone / Q000494:pharmacology; D006107:Granulosa Cells / Q000187:drug effects / Q000378:metabolism*; D006736:Horses / Q000378:metabolism*; D007328:Insulin / Q000494:pharmacology; D018971:Insulin-Like Growth Factor Binding Protein 2 / Q000096:biosynthesis; D018975:Insulin-Like Growth Factor Binding Protein 5 / Q000096:biosynthesis; D018969:Insulin-Like Growth Factor Binding Proteins / Q000096:biosynthesis*; D007334:Insulin-Like Growth Factor I / Q000096:biosynthesis*; D007335:Insulin-Like Growth Factor II / Q000096:biosynthesis*; D006080:Ovarian Follicle / Q000033:anatomy & histology*; D011374:Progesterone / Q000096:biosynthesis; D013256:Steroids / Q000096:biosynthesis*
chemical_list: D003470:Culture Media; D016895:Culture Media, Serum-Free; D007328:Insulin; D018971:Insulin-Like Growth Factor Binding Protein 2; D018975:Insulin-Like Growth Factor Binding Protein 5; D018969:Insulin-Like Growth Factor Binding Proteins; D013256:Steroids; D011374:Progesterone; D004958:Estradiol; D007334:Insulin-Like Growth Factor I; D007335:Insulin-Like Growth Factor II; D005640:Follicle Stimulating Hormone