Regulation of DNA synthesis in goldfish vitellogenic ovarian follicles by hormones and growth factors

Abstract The present study examines the effects of selected hormones and growth factors on deoxyribonucleic acid (DNA) synthesis by goldfish vitellogenic and prematurational full‐grown ovarian follicles in vitro. The synthesis of DNA was assessed from the incorporation of [ 3 H]‐thymidine after preincubation in medium supplemented with fetal bovine serum, followed by a second incubation in serum‐free medium with several combinations of hormones and growth factors. DNA synthesis by vitellogenic ovarian follicles was enhanced by the addition of ovine and porcine insulin (0.4–40 μg/ml) and human recombinant insulin‐like growth factor I (IGF‐I, 12.5–100 ng/ml) and IGF‐II (50–100 ng/ml); the order of potency was IGF‐I > IGF‐II > insulin. The interactive effects of insulin, IGF‐I, and IGF‐II on DNA synthesis by vitellogenic follicles were additive, suggesting that these peptides may act through distinct receptors. By comparison, both insulin (4 μg/ml) and IGF‐I (100 ng/ml) had no effect on DNA synthesis by prematurational full‐grown follicles, suggesting that sensitivity of ovarian follicles to insulin and IGF‐I may change during follicular development. IGF‐I (25–200 ng/ml) and IGF‐II (25–200 ng/ml) had no effect on basal and human chorionic gonadotropin (hCG)‐stimulated testosterone and 17β‐estradiol production by vitellogenic follicles, suggesting that these growth factors may play a role in regulating follicular DNA synthesis but not ovarian steroidogenesis. Carp gonadotropins (cGtH‐I and cGtH‐II), hCG, and 17β‐estradiol also enhanced DNA synthesis by vitellogenic follicles. The effects of hCG and 17β‐estradiol on DNA synthesis were further enhanced in the presence of either insulin or IGF‐I. In conclusion, these data provide convincing evidence of the mitogenic actions of insulin, IGFs, gonadotropins, and 17β‐estradiol, suggesting that these hormones and growth factors may regulate follicular growth and development in the goldfish. © 1994 Wiley‐Liss, Inc.