Circulating insulin-like growth factors (IGF-I and -II) and IGF binding proteins in divergently selected fat or lean chickens: effect of prolonged fasting.

Possible differences in insulin-like growth factors (IGF-I and -II) and their binding proteins (IGFBPs) were investigated in genetically fat or lean chickens. Comparisons were performed at 9 weeks of age in the fed or the fasted (48 h) state. Plasma concentrations of both IGFs were altered by nutrition and genotype. IGF-I, and to a lower extent IGF-II, decreased following fasting. IGF-I and -II were higher in fat compared to lean chickens, in both the fasted and the fed states. Of four circulating IGFBPs with molecular weights of 28, 34, 40 and 60 kDa, IGFBP-28, and to a lesser extent IGFBP-34 and -60, increased in the fasted state. No consistent differences were observed between genotypes for IGFBPs. Therefore in chickens, as in mammals, IGFs are downregulated, and IGFBP-28 upregulated by fasting. An increase in IGFs levels in Fat chickens may contribute to enhance fat deposition in this genotype.