COMPARISON OF SANDWICH ENZYME-LINKED IMMUNOADSORBENT ASSAY AND RADIOIMMUNOASSAY FOR DETERMINATION OF EXOGENOUS GLUCAGON-LIKE PEPTIDE-1(7-36)AMIDE IN PLASMA

A sensitive sandwich enzyme-linked immunoadsorbent assay (ELISA) for d etermination of exogenous glucagon-like peptide-1(7-36)amide (GLP-1(7- 36)amide) in plasma samples from pharmacokinetic studies is described. The assay employs an N-terminally directed antibody and a C-terminall y directed antibody. The ELISA has a working range from 10 to 500 pmol l(-1), and can be applied to plasma samples from humans, dogs, pigs, minipigs, cats, rabbits, and rats. The assay was compared to a validat ed radioimmunoassay (RIA), employing an antibody directed against the mid-region of GLP-1. After s.c. administration of GLP-1(7-36)amide, th e plasma immunoreactivity of GLP-1 (P-GLP-1-IR) measured by ELISA was markedly lower than P-GLP-1-IR measured by RIA. After HPLC fractionati on of plasma samples with subsequent RIA and ELISA analyses of the fra ctions, this difference was shown to be due to cross reaction with bio logically inactive fragments of GLP-1(7-36)amide in the RIA but not in the ELISA.