Influence of gonadotropins on insulin- and insulin-like growth factor-I (IGF-I)-induced steroid production by bovine granulosa cells.
To determine the effect of gonadotropins on insulin- and insulin-like growth factor (IGF-I)-induced bovine granulosa cell functions, granulosa cells from bovine ovarian follicles were cultured for 2 days in the presence of 10% fetal calf serum (FCS), and then cultured for an additional 2 days in serum-free medium with added hormones. In the presence of 0 or 1 ng/mL of insulin or IGF-I, FSH had little or no effect (P > 0.05) on estradiol production by granulosa cells from both small (1-5mm) and large (> or = 8mm) follicles. However, in the presence of > or = 3 ng/mL of insulin, FSH increased (P < 0.05) estradiol production by granulosa cells from small and large follicles such that the estimated dose (ED(50)) of insulin necessary to stimulate 50% of the maximum estradiol production was decreased by 2- to 3-fold from 22 to 28 ng/mL in the absence of FSH to 7-14 ng/mL in the presence of FSH. Similarly, in the presence of > or = 3 ng/mL of IGF-I, FSH increased (P< 0.05) estradiol production by granulosa cells from small and large follicles such that the ED(50) of IGF-I for estradiol production was decreased by 4- to 5-fold from 25 to 36 ng/mL in the absence of FSH to 5-6 ng/mL in the presence of FSH. In the presence of FSH, the maximal effect of insulin on estradiol production was much greater than that of IGF-I (137- versus 12-fold increase) and were not additive; when combined, 100 ng/mL of IGF-I completely blocked the stimulatory effect of 100 ng/mL of insulin. In the absence of FSH, the maximal effect of insulin and IGF-I on estradiol production was similar. Concomitant treatment with 30 ng/mL of LH reduced (P<0.05) insulin-stimulated estradiol production by 52% on day 1 and 19% on day 2 of treatment. Insulin, IGF-I and FSH also increased (P<0.05) granulosa cell numbers and progesterone production but their maximal effects were less (i.e., < 4-fold increase) than their effects on estradiol production. In conclusion, insulin and IGF-I synergize with FSH to directly regulate ovarian follicular function in cattle, particularly granulosa cell aromatase activity.
Spicer
Leon J
LJ
Department of Animal Science, Oklahoma State University, Stillwater, OK 74078, USA. igf1leo@okstate.edu
Chamberlain
Connie S
CS
Maciel
Sonia M
SM
D000818:Animals; D001141:Aromatase / Q000378:metabolism; D002417:Cattle / Q000378:metabolism*; D002452:Cell Count; D002478:Cells, Cultured; D003470:Culture Media; D004305:Dose-Response Relationship, Drug; D004958:Estradiol / Q000096:biosynthesis; D005260:Female; D005640:Follicle Stimulating Hormone / Q000494:pharmacology; D006065:Gonadotropins, Pituitary / Q000494:pharmacology*; D006107:Granulosa Cells / Q000187:drug effects* / Q000378:metabolism; D007328:Insulin / Q000494:pharmacology*; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology*; D007986:Luteinizing Hormone / Q000494:pharmacology; D011374:Progesterone / Q000096:biosynthesis; D013256:Steroids / Q000096:biosynthesis*
D003470:Culture Media; D006065:Gonadotropins, Pituitary; D007328:Insulin; D013256:Steroids; D011374:Progesterone; D004958:Estradiol; D007334:Insulin-Like Growth Factor I; D007986:Luteinizing Hormone; D005640:Follicle Stimulating Hormone; D001141:Aromatase