A HOMOLOGOUS RADIOIMMUNOASSAY FOR RAT INSULIN-LIKE GROWTH-FACTOR-I (IGF-I) - IMPLICATIONS FOR STUDIES OF HUMAN IGF-I PHYSIOLOGY

We report the development of a unique radioimmunoassay (RIA) for rat i nsulin-like growth factor-I (rIGF-I) which does not recognize human IG F-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 vir tually identical results. Assay sensitivity is (similar to)0.5 ng/tube and inter- and intra- assay coefficients of variation were 3.4-7.6% a nd 4.8-9.2%, respectively. Comparisons of the rIGF-I RIA with a typica l heterologous RIA shows that the latter underestimates rIGF-I levels by (similar to)3-fold. Sera from rats treated with hIGF-I were also st udied using the rIGF-I RIA and a hIGF-I-specific immunoradiometric ass ay (IRMA), and results indicate poor correlation between the actual to tal IGF-I levels (rIGF-I RIA + hIGF-IRMA) and the heterologous RIA est imates. The availability of both rIGF-I and hIGF-I specific immunoassa ys facilitates more precise studies of hIGF-I in the rat model.