Description and application of a novel glucagon-like peptide-1 (GLP-1) radioimmunoassay

Abstract

The gut hormone glucagon-like peptide-1 (GLP-1) is derived from the transcription product of the proglucagon gene in the intestinal L cells. The known physiological functions of this peptide include: increases insulin and decreases glucagon secretion from the pancreas, furthermore promotes insulin sensitivity. Our research group working on diabetes and obesity, considered that it is important to develop an own specific and sensitive GLP-1 radioimmunoassay (RIA) method. The antiserum (GLP3/7), sensitive to the C-terminal region of peptide was produced by the immunization of rabbits administering GLP-1(19-37)-bovine serum albumin antigen subcutaneously. To show the antibody attachment we used iodogen method labelled mono-¹²⁵I-GLP-1(19-37). GLP-1(19–37) peptide was used as standard for the RIA determination in a range of 0–1000 fm/ml. Our new RIA method was applied in an insulin resistance animal model. In the experiment Sprague-Dawley rats were treated with olanzapine (per os) 5 mg/kg body weight once a day for four weeks. Finally, in a glucose uptake experiment blood glucose and plasma GLP-1 levels were measured. After ten measurements the D₅₀ value of the calibration curves was 15.18 ± 2.02 fmol/ml. The detection limit of our method was 0.4 fmol/ml GLP-1. The cross-reactivity studies showed that the antiserum used in our RIA method has a limited cross-reactivity with other peptides with similar structure. The difference of fasting blood glucose and GLP-1 plasma levels between control and olanzapine-treated animals were not significant, while blood glucose concentration was increased GLP-1 plasma level was significantly decreased during glucose uptake.