Regulation of Steroidogenesis in Cultured Porcine Theca Cells by Growth Factors*

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Abstract
Growth factors [insulin-like growth factors (IGF-I, IGF-II), transforming growth factor-.beta. (TGF.beta.), epidermal growth factors (EGF)], found in the ovary and known to alter granulosal function, were assessed for their ability to modulate porcine thecal steroidogenesis. Theca cells from large porcine follicles (8-10 mm) were plated (5 .times. 105 cells/ml .cntdot. well) in serum-free M199, treated with increasing doses of growth factors: IGF-I (0.1-50 ng/ml), IGF-II (0.5-200 ng/ml), EGF (0.021-100 ng/ml), TGF.beta. (0.001-40 ng/ml), or insulin (0.01-50 .mu.g/ml), with or without human CG [(hCG); 20 ng/ml], and incubated for 72 h. Levels of steroids in media were determined by RIA. Insulin increased (P < 0.05) basal and gonadotropin-induced secretion of androstenedione, progesterone, estradiol, and testosterone. IGF-I increased (P < 0.05) the basal and hCG-induced secretion of progesterone and androstenedione at the highest doses, but did not affect basal secretion of estradiol or testosterone. IGF-II, at the highest doses, increased (P < 0.05) thecal steroidogenesis, but only after administration of hCG. In contrast, TGF.beta. increased (P < 0.05) basal and gonadotrophin-induced secretion of estradiol but inhibited thecal secretion of progesterone, androstenedione, and testosterone. EGF did not alter thecal secretion of progesterone, androstenedione, or testosterone but significantly (P < 0.05) inhibited basal and hCG-stimulated secretion of estradiol. In conclusion, insulin, IGF-I, IGF-II, EGF, and TGF.beta. can modulate steroidogenesis in porcine theca cells.

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