ONTOGENY OF INSULIN-LIKE GROWTH-FACTORS (IGF-I AND IGF-II) AND IGF-BINDING PROTEINS IN THE CHICKEN FOLLOWING HATCHING

The present study examined plasma concentrations of insulin-like growt h factor (IGF)-I, IGF-II and IGF-binding proteins (IGFBPs) during post hatch growth and development in chickens. Three distinct proteins whic h bound I-125-IGF-I were observed irrespective of age or sex, these ha ving apparent molecular weights of 22, 28, and 36 kDa. The major IGFBP present during much of the growth and development period was the 28-k Da form followed by the 36-kDa form. Plasma concentrations of IGF-II a nd of the 22-kDa IGFBP showed little ontogenic variation with the exce ption of elevated levels of the 22 kDa IGFBP in 1-day-old chicks. The circulating concentrations of IGF-I and of the 28-kDa IGFBP increased progressively between the time of hatching to reach a maximum at 6 wee ks of age and subsequently declined to lower levels in adults. Some wh at similarly the 36-kDa IGFBP increased during early pre- and posthatc hing growth to a maximum at 6 weeks of age. There were marked sex diff erences in circulating concentrations of IGF-I in young (4 week) and a dult chickens and in the 36-kDa IGFBP in the adult, both being lower i n females. Estrogen treatment of adult male chickens decreased the cir culating concentrations of IGF-I together with the level of both the 2 8- and 36-kDa IGFBPs. Testosterone treatment had no effect on the circ ulating concentrations of either IGF-I or IGFBPs in adult female chick ens. We conclude that the relative levels of IGF-I, IGF-II, and the IG FBPs change with age. In addition, circulating concentrations of estro gen may play a role in the regulation of IGF-I and IGFBPs. (C) 1997 Ac ademic Press.