Opposite effects of insulin-like growth factors (IGFs) on gonadotropin (GtH-II) and growth hormone (GH) production by primary culture of European eel(Anguilla anguilla) pituitary cells

Insulin-like growth factor-I (IGF-I) is a growth factor mainly produced by the liver under the control of growth hormone (GH) and implicated in the me diation of body growth regulation in teleosts as in other vertebrates. Its possible role in the interaction between growth and reproduction was invest igated, by comparing its effects on GH and gonadotropin (GtH-II) production s, in juvenile sexually immature eels. This study was performed in vitro on primary culture of pituitary cells; to avoid effects of other growth facto rs, cells were cultured with basic culture medium (M199) without addition o f serum. Eel GH and GtH-II levels in cells and media were measured by speci fic RIAs. Control cells released a large amount of GH, and after 2 weeks le vels were more than twofold the initial cell content indicating a high prod uction of GH by cultured cells. IGF-I inhibited GH release and production i n a time- and dose-dependent manner. A maximal effect (> 80% inhibition) wa s reached at 10(-9) M. Initial GtH-II cell content was at least 1000 times lower than GH cell content, and the amount released in 2 weeks reached only a few percent of cell content. IGF-I stimulated GtH-II cell content and re lease in a time- and dose-dependent manner. A maximal stimulation of GtH-II production (up to x 6) was observed at 10(-8) M after 2 weeks of culture. IGF-II, showed the same potency as IGF-I to reduce GH production and stimul ate GtH-II production. These results indicate opposite effects of IGFs on G H and GtH-II productions in eel pituitary cells and suggest that IGF-I may play an interface between growth and reproduction (puberty) in juvenile tel eosts. (C) 1999 Elsevier Science B.V. All rights reserved.