Insulin-like growth factor-I stimulates gonadotrophin production from eel pituitary cells: a possible metabolic signal for induction of puberty.
Insulin-like growth factor (IGF)-I has been suggested as a potential signal linking growth and puberty in mammals. Using the juvenile European eel as a model, we employed a long-term, serum-free primary culture of pituitary cells to study the direct effect of IGF-I on gonadotrophin (GtH-II=LH) production. IGF-I increased both cell content and release of GtH-II in a time- and dose-dependent manner. IGF-I and IGF-II had similar potencies but insulin was 100-fold less effective, suggesting the implication of an IGF type 1 receptor. Other growth and metabolic factors, such as basic fibroblast growth factor and thyroid hormones, had no effect on GtH-II production. IGF-I did not significantly increase the number of GtH-II immunoreactive cells, indicating that its stimulatory effect on GtH-II production does not result from gonadotroph proliferation. Comparison of IGF-I and somatostatin (SRIH-14) effects showed that both factors inhibited growth hormone (GH) release but only IGF-I stimulated GtH-II production by eel pituitary cells. This indicates that the effect of IGF-I on gonadotrophs is not mediated by the reduction of GH released by somatotrophs into the culture medium. This study demonstrates a specific stimulatory effect of IGF-I on eel GtH-II production, played out directly at the pituitary level. These data obtained in a primitive teleost suggest that the role of IGF-I as a link between body growth and puberty may have been established early in the evolution of vertebrates.
Huang
Y S
YS
Laboratoire de Physiologie Générale et Comparée, Muséum National d'Histoire Naturelle, URA 90 CNRS, 7 rue Cuvier, 75231 Paris Cedex 05, France.
Rousseau
K
K
Le Belle
N
N
Vidal
B
B
Burzawa-Gérard
E
E
Marchelidon
J
J
Dufour
S
S
D000704:Analysis of Variance; D000818:Animals; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D004524:Eels / Q000378:metabolism*; D005260:Female; D006065:Gonadotropins, Pituitary / Q000096:biosynthesis*; D013006:Growth Hormone / Q000096:biosynthesis; D007150:Immunohistochemistry; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology*; D010902:Pituitary Gland / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D012741:Sexual Maturation / Q000502:physiology*; D013268:Stimulation, Chemical; D013997:Time Factors
D006065:Gonadotropins, Pituitary; D007334:Insulin-Like Growth Factor I; D013006:Growth Hormone