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 Cells1

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.

Follicular blood flow, antrum growth and angiogenic mediators in mares from ovulation to deviation

“…The plateau of increased IGF-1 after ovulation from day 3 to day 5 during follicle selection and its increase again during and after deviation supports the role of IGF-1 in follicle selection and deviation. Within the equine ovary, the production of insulin like growth factors (IGF-I, IGF-II) and insulin like growth factor binding proteins (IGFBP-2, IGFBP-5) by granulosa cells and estradiol confirmed their role in the regulation of steroidogenesis and the IGF system (Davidson et al, 2002). In agreement with our results, the lowest concentration of IGFBPs indicated high free IGFs and dominance (Mihm et al, 2000), and selection (Mazerbourg et al, 2003).…”

Effects of decreased estradiol-17β on the serum and anterior pituitary IGF-I system in pigs

“…During the estrous cycle in ewes, expression of IGFBP-5 in the uterine luminal epithelium and inner myometrium has been found to increase around ovulation and decrease during the late luteal phase (Gadd et al 2000), times coincident with increased and decreased circulating concentrations of estradiol respectively. Administration of E2 to equine granulosa cells also increased relative amounts of IGFBP-2 (Davidson et al 2002). Thus, E2 appears to be a regulator of relative amounts and expression of IGFBP-2 and -5.…”

Participación del sistema IGF en la patogenia de la enfermedad quística bovina

“…El desarrollo folicular está regulado principalmente por la FSH y la LH, y el sistema IGF actúa en sinergia con dichas hormonas, estimulando la diferenciación celular Davidson et al, 2002). La regulación de la foliculogénesis es un proceso complejo en el cual los IGFs son relevantes por la interrelación con la FSH, hormonas esteroides, otros factores de crecimiento y hormonas que controlan el desarrollo folicular (Souza et al, 2007).…”

“…El desarrollo folicular está regulado principalmente por la hormona foliculoestimulante (FSH) y la hormona luteinizante (LH), sin embargo existen evidencias que indican que los factores de crecimiento como el sistema de factores de crecimiento análogos a insulina (IGF), actúan en sinergia con las gonadotropinas y pueden actuar localmente en las células del folículo promoviendo o atenuando la diferenciación celular (Giudice, 1992;Spicer y Echternkamp, 1995;Monget, 1996;Adashi, 1998;Davidson et al, 2002;Brogan et al, 2010).…”