Effects of gonadotropins and insulin-like growth factors-I and -II on in vitro steroid production by bovine granulosa cells

Abstract

The objectives of this study were: 1) to develop a bovine granulosa cell (GC) culture system; and 2) to use this system to evaluate the effects of gonadotropins (FSH and LH) and insulin-like growth factors-I and -II (IGF-I and IGF-II) on steroidogenesis of bovine GC derived from small, medium, and large antral follicles (diameters ≤4, 5–8 and >8 mm, respectively). Granulosa cells were cultured (concentration, 5 × 105 cells per well) in serum-free medium for 48 h with variable doses of hormones and growth factors. Concentrations of progesterone (P4) and estradiol-17β (E2) in the media were determined by radioimmunoassay. Basal E2 production by GC from follicles of all sizes decreased with time of culture (P < 0.01) while basal P4 production increased (P < 0.01). Basal E2 and P4 production increased with increasing size of follicles (P < 0.01). Only very low concentrations of FSH stimulated E2 production from medium and large follicles. Follicle-stimulating hormone stimulated P4 production by GC of follicles of all sizes (P < 0.05). Luteinizing hormone inhibited E2 production by GC in medium and large follicles (P < 0.05), suggesting that LH is responsible for the rise in plasma E2 through effects on both theca cells and GC. A dose of 100 ng mL−1 of IGF-I increased E2 production by GC from medium and large follicles (P < 0.05). Progesterone production by GC from all categories of follicles was also stimulated by IGF-I (P < 0.05). Estradiol-17β production by GC from large follicles decreased in response to IGF-II (P < 0.05). The physiological role of IGF-II on steroidogenesis in the bovine ovary remains to be elucidated. In summary, these results demonstrate the development of a serum-free culture system for bovine GC, and that FSH, LH, IGF-I and IGF-II have different effects on steroidogenesis by bovine GC from different size follicles. Key words: Granulosa cells, gonadotropins, Insulin-like growth factors, progesterone, estradiol-17β, cows