Influence of dietary protein on insulin-like growth factor binding proteins in the chicken

We determined the effect of dietary protein on the distribution of insulin- like growth factor (ICF) binding proteins in chicken plasma. Three groups o f male broilers (n = 6 per group) were fed (ad libitum) isocaloric diets co ntaining 12, 21 or 30% dietary protein. Birds were fed respective diets beg inning at 7 days of age and killed at 28 days. No differences were observed between adequate (21%,) and high (30%) protein intakes for any of the para meters investigated (growth criteria, plasma levels of IGF-I, growth hormon e or IGF-binding proteins). Feeding protein deficient diets (12%) resulted in a 34% decrease in body weight, 17% decrease in feed intake and a 39% inc rease in feed/gain ratio. IGF-binding proteins in plasma samples were separ ated by SDS-PAGE and transferred to nitrocellulose sheets. Nitrocellulose b lots were probed with [I-125]chicken IGF-II. Four regions of binding activi ty corresponding to 70, 43, 30 and 24 kDa were observed in all samples. Bir ds consuming 12% dietary group protein had less than 50% of the 33-kDa bind ing activity of birds consuming 21 or 30% dietary protein. The 30-kDa bindi ng activity was 42%, lower in the 12% dietary protein group compared to bir ds consuming adequate protein. In contrast, 70- and 24-kDa binding activiti es were not influenced by dietary protein. Chickens consuming 12% dietary p rotein had higher levels of growth hormone and lower levels of TGF-I than t hose consuming 21 or 30% dietary protein. These data indicate that in chick ens, the circulating levels of at least two independent IGF-binding protein s are influenced by dietary protein. (C) 1999 Elsevier Science Inc. All rig hts reserved.