A homologous radioimmunoassay for rat insulin-like growth factor-I (IGF-I): implications for studies of human IGF-I physiology

J Clin Endocrinol Metab. 1996 May;81(5):2002-5. doi: 10.1210/jcem.81.5.8626873.


We report the development of a unique radioimmunoassay (RIA) for rat insulin-like growth factor-I (rIGF-I) which does not recognize human IGF-I (hIGF-I). The rIGF RIA uses a specific anti-rIGF-I antiserum with rIGF-I standards and radioligand. Rat sera were extracted by either an abbreviated acid/ethanol procedure or by acid-chromatography with virtually identical results. Assay sensitivity is congruent to 0.5 ng/tube and inter- and intra-assay coefficients of variation were 3.4-7.6% and 4.8-9.2%, respectively. Comparisons of the rIGF-I RIA with a typical heterologous RIA shows that the latter underestimates rIGF-I levels congruent to of 3-fold. Sera from rats treated with hIGF-I were also studied using the rIGF-I RIA and a hIGF-I- specific immunoradiometric assay (IRMA), and results indicate poor correlation between the actual total IGF-I levels (rIGF-I RIA + hIGF-IRMA) and the heterologous RIA estimates. The availability of both rIGF-I and hIGF-I specific immunoassays facilitates more precise studies of hIGF-I in the rat model.

Publication types

  • Comparative Study

MeSH terms

  • Animals
  • Cricetinae
  • Humans
  • Insulin-Like Growth Factor I / analysis*
  • Insulin-Like Growth Factor II / analysis
  • Mice
  • Radioimmunoassay / methods*
  • Radioimmunoassay / statistics & numerical data
  • Rats
  • Sensitivity and Specificity
  • Species Specificity


  • Insulin-Like Growth Factor I
  • Insulin-Like Growth Factor II