Radio-immunoassays for glucagon-like peptides 1 and 2 (GLP-1 and GLP-2)

Abstract

Gene-sequencing studies have shown that the glucagon precursor contains two additional glucagon-like sequences, the so-called glucagon-like peptides 1 and 2 (GLP-1 and GLP-2). We developed radio-immunoassays against synthetic peptides corresponding to these sequences. Antisera were raised in rabbits after carbodiimide conjugation of peptides to BSA. The selected antisera showed neither mutual cross-reactivity nor cross-reacted with any other peptide of the glucagon family. Trypsin digestion experiments showed that both antisera were directed against the C-terminus of the antigen peptides. Labelling was performed with chloramine T, and separation with plasma-coated charcoal. The detection limit was 7 and 25 pmol/l for GLP-1 and GLP-2. Accurate measurement of both peptides in plasma required extraction. Optimum recovery was obtained with ethanol at 75% (final concentration). The concentrations measured in fasting plasma from 10 normal subjects were 107 +/- 7 pmol/l and 151 +/- 14 pmol/l for GLP-1 and GLP-2, respectively. After a mixed meal the concentrations rose slowly for 2 h reaching 145 +/- 13 and 225 +/- 15 pmol/l.