DEVELOPMENTAL-CHANGES IN CHICKEN AND TURKEY INSULIN-LIKE GROWTH-FACTOR-I (ICF-I) STUDIED WITH A HOMOLOGOUS RADIOIMMUNOASSAY FOR CHICKEN IGF-I

The development of a homologous radioimmunoassay (RIA) for chicken ins ulin-like growth factor-I (cIGF-I) and its use to investigate the deve lopmental changes in IGF-I in the chicken and turkey is described. A d ouble antibody RIA has been developed using recombinantly derived cIGF -I as antigen, radiolabelled tracer and standard. The resulting immuno assay has a minimum detection limit of 0.035 ng and effective dose of 2.5 ng. Dose-response curves of chicken and turkey plasma and tissue e xtracts were parallel with cIGF-I standard. The antiserum is specific for IGF-I as no cross-reactivity with chicken IGF-II, insulin, glucago n, gastrin or avian pancreatic polypeptide was observed. We have also established that acid/ethanol extraction of chicken and turkey plasma reduced possible interference of IGF-binding proteins (IGFBPs) in the RIA. Comparison of IGF-I immunoactivity in unextracted and acid/ethano l-extracted samples following gel filtration under acidic and neutral conditions indicates that the cIGFBPs may be acid-labile. Analyses of samples from growing chickens and turkeys using the homologous avian r eagents revealed higher IGF-I concentrations than if the IGF were quan tified using heterologous mammalian-derived reagents. A similar patter n was observed when tissue extracts were assayed for IGF-I content. Th e application of the homologous IIIA to monitor blood and tissue IGF-I levels during embryonic development and posthatch growth in avian spe cies will provide more accurate comparisons oi results from studies on the role of IGF-I in growth and metabolism of domestic birds.