Influence of nutrition on hepatic IGF-I mRNA levels and plasma concentrations of IGF-I and IGF-II in meat-type chickens

Abstract

<jats:title>Abstract</jats:title> <jats:p>We have examined the influence of nutrition on plasma IGF-I, IGF-II and IGF-binding protein (IGFBP) levels and on hepatic IGF-I gene expression in young meat-type chickens. Plasma IGF concentrations were measured by using RIA with recombinant chicken IGFs as standards.</jats:p> <jats:p>In chickens fed the control diet containing 200 g/kg dietary protein <jats:italic>ad libitum</jats:italic> for 7 days, plasma IGF-I concentrations increased significantly from those found in the initial control group. Food restriction for either 4 or 7 days decreased plasma IGF-I by 30% from the initial control. When chickens were refed <jats:italic>ad libitum</jats:italic> for 3 days after 4 days of restricted feeding, plasma IGF-I levels recovered to those of the control birds fed <jats:italic>ad libitum</jats:italic>. In chickens eating a low protein diet (100 g/kg protein), the plasma IGF-I tended to be lowered but the decrease was not significant. Although the intensity of IGF-I and β-actin mRNA bands protected in the RNase protection assay was changed by nutrition, no statistical effect of nutrition on the ratio of IGF-I to β-actin was observed. The nutritional treatments had no effect on plasma IGF-II concentrations.</jats:p> <jats:p>Western ligand blot and chromatographic analyses were used to investigate the influence of nutrition on IGFBP profiles. Both IGF-I and IGF-II ligands in the Western ligand blot revealed the most intense binding at 30 kDa for plasma obtained from chickens with restricted food intake. The 30 kDa band also appeared at a lower intensity in the group fed a low protein diet but not in any other groups. These observations were confirmed by neutral gel chromatography. The chicken IGF-II ligand revealed an intensely labelled band corresponding to 75 kDa and this was not affected by nutrition.</jats:p> <jats:p>IGF-I and IGFBP concentrations in the plasma of young broiler chickens were influenced by nutritional state but IGF-II concentrations were not. The lack of a response in circulating IGF-II levels may have been due to the presence of high concentrations of a 75 kDa specific binding protein which did not respond to nutrition in this experiment.</jats:p> <jats:p><jats:italic>Journal of Endocrinology</jats:italic> (1996) <jats:bold>149,</jats:bold> 181–190</jats:p>