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Details

Autor(en) / Beteiligte
Titel
Influence of gonadotropins on insulin- and insulin-like growth factor-I (IGF-I)-induced steroid production by bovine granulosa cells
Ist Teil von
  • Domestic animal endocrinology, 2002-06, Vol.22 (4), p.237-254
Ort / Verlag
United States: Elsevier Inc
Erscheinungsjahr
2002
Quelle
Elsevier ScienceDirect Journals
Beschreibungen/Notizen
  • 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 (1–5 mm) and large (≥8 mm) follicles. However, in the presence of ≥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 ≥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.

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