Receptors for insulin-like growth factor-I and tumor necrosis factor-α are hormonally regulated in bovine granulosa and thecal cells

Mastitis induces release of tumor necrosis factor-α (TNFα) and has been linked with reduced reproductive performance. To further elucidate the role and mechanism of action of TNFα on ovarian cells, the effect of TNFα on insulin-like growth factor-I (IGF-I)-induced steroidogenesis and IGF-I binding sites in granulosa and thecal cells as well as the hormonal regulation of TNFα receptors were evaluated. Granulosa and thecal cells were obtained from small (1–5 mm) and large (≥8 mm) bovine ovarian follicles, respectively, and cultured for 3–4 days. During the last 2 days of culture, cells were treated with various hormones and steroid production and specific binding of 125I-IGF-I and 125I-TNFα was determined. Two-day treatment with 30 ng/ml of TNFα decreased (P<0.05) IGF-I-induced estradiol production by granulosa cells and IGF-I-induced androstenedione production by thecal cells. Two-day treatment with 10 and 30 ng/ml of TNFα decreased (P<0.05) specific binding of 125I-IGF-I to thecal cells, but had no effect on specific binding of 125I-IGF-I to granulosa cells, or on specific binding of 125I-IGF-II to thecal cells. TNFα did not compete for 125I-IGF-I binding to granulosa or thecal cells whereas unlabeled IGF-I suppressed 125I-IGF-I binding. Insulin inhibited (P<0.10) whereas FSH had no effect on the number of specific 125I-TNFα binding sites in granulosa cells. In contrast, LH increased (P<0.10) whereas insulin had no effect on specific 125I-TNFα binding sites in thecal cells. These results suggest that IGF-I and TNFα receptors in granulosa and thecal cells are regulated by hormones differentially.