Hormonal regulation of the peripubertal surge of insulin-like growth factor-I in the rat.
The marked increase in circulating insulin-like growth factor-I (IGF-I) levels during puberty observed in primates indicates an important functional relationship between hypothalamic-pituitary gonadal function and hormonal regulation of peripubertal circulating IGF-I levels. Recent studies demonstrating local production and secretion of gonadal peptides including IGF-I suggest that increased circulating IGF-I levels during puberty might be due to direct gonadal secretion of IGF-I or alternatively to indirect effects of increased gonadal steroid secretion on nongonadal tissues including the hypothalamus, pituitary, and liver. We therefore studied the effects of prepubertal castration on the pubertal IGF-I surge and demonstrate that castration provokes a further increase rather than ablation of the pubertal IGF-I surge in the rat. Furthermore, neonatal treatment with monosodium glutamate, a hypothalamic neurotoxin, abolishes the pubertal IGF-I surge when commenced on postnatal day 1 but not on day 5, whereas treatment with a GnRH antagonist commencing within 12 h of birth significantly reduces but does not abolish the pubertal IGF-I surge. We therefore propose that the pubertal IGF-I surge in the rat is not due to direct gonadal secretion of IGF-I or other gonadal hormones during puberty but may involve hypothalamic and/or hepatic programming by events during prenatal or very early postnatal life.
D000818:Animals; D000831:Animals, Newborn; D005260:Female; D007987:Gonadotropin-Releasing Hormone / Q000031:analogs & derivatives* / Q000494:pharmacology; D007334:Insulin-Like Growth Factor I / Q000097:blood / Q000378:metabolism*; D007986:Luteinizing Hormone / Q000097:blood; D008297:Male; D009919:Orchiectomy; D009929:Organ Size; D010052:Ovariectomy; D051381:Rats; D011920:Rats, Inbred WF; D012737:Sex Factors; D012741:Sexual Maturation; D013002:Somatomedins / Q000378:metabolism*; D013739:Testosterone / Q000097:blood
D013002:Somatomedins; D007987:Gonadotropin-Releasing Hormone; D013739:Testosterone; C010661:surfagon; D007334:Insulin-Like Growth Factor I; D007986:Luteinizing Hormone