ASSESSMENT OF DEVELOPMENTAL-CHANGES IN CHICKEN AND TURKEY INSULIN-LIKE GROWTH-FACTOR-II BY HOMOLOGOUS RADIOIMMUNOASSAY

The development of a homologous RIA for chicken insulin-like growth fa ctor-II (cIGF-II) and its application to investigate the developmental changes in IGF-II in the chicken and turkey are described. A double-a ntibody RIA has been developed using recombinantly derived cIGF-II as antigen, radiolabelled tracer and standard. Serial dilutions of chicke n and turkey plasma were parallel to serial dilutions of cIGF-II stand ard. We have also established that acid/ethanol extraction of chicken and turkey plasma reduced possible interference of insulin-like growth factor-binding proteins in the RIA. Consumption of a low-protein diet by male chickens lowered plasma IGF-I twofold, whereas IGF-II levels were unchanged. Food withdrawal evoked an increase in circulating IGF- II, while IGF-I levels were reduced. Refeeding returned both growth fa ctors to normal circulating concentrations. During chick embryo incuba tion, plasma IGF-II levels were tenfold higher than those of IGF-I. In the turkey embryo, plasma IGF-II concentrations were higher than thos e of IGF-I. During the post-hatch period, IGF-II levels declined with age in chickens. In the growing turkey, IGF-II levels were consistentl y higher than IGF-I levels. The application of the homologous RIA to m onitor plasma levels during embryonic development and posthatch growth in avian species will provide more accurate comparisons of results fr om studies on the role of IGF-II in growth and metabolism of domestic birds.