McMurtry J P, Francis G L, Upton F Z, Rosselot G, Brocht D M
United States Department of Agriculture, Nonruminant Animal Nutrition Laboratory, Beltsville, Maryland 20705.
J Endocrinol. 1994 Aug;142(2):225-34. doi: 10.1677/joe.0.1420225.
The development of a homologous radioimmunoassay (RIA) for chicken insulin-like growth factor-I (cIGF-I) and its use to investigate the developmental changes in IGF-I in the chicken and turkey is described. A double-antibody RIA has been developed using recombinantly derived cIGF-I as antigen, radiolabelled tracer and standard. The resulting immunoassay 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 extracts were parallel with cIGF-I standard. The antiserum is specific for IGF-I as no cross-reactivity with chicken IGF-II, insulin, glucagon, 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/ethanol-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 reagents revealed higher IGF-I concentrations than if the IGF were quantified using heterologous mammalian-derived reagents. A similar pattern was observed when tissue extracts were assayed for IGF-I content. The application of the homologous RIA to monitor blood and tissue IGF-I levels during embryonic development and posthatch growth in avian species will provide more accurate comparisons of results from studies on the role of IGF-I in growth and metabolism of domestic birds.
