Glucagon-Like Peptide-1 in the Rat Pancreas

The concentration, molecular forms, distribution and release of the glucagon-like peptide (GLP)-1, encoded by the mammalian preproglucagon gene, in the rat pancreas were investigated by newly developed specific radioimmunoassay and immunocytochemistry. Both the GLP-1-like immunoreactivity and immunoreactive glucagon (IRG) values in the rat pancreas extract obtained by Kenny’s extraction method were higher than those obtained by the acid boiling method. Using the former method, the concentrations of GLP-1-like immunoreactivity and IRG were 209±66 nｇ/ｇ wet weight and 3,740±760 nｇ/ｇ wet weight, respectively. On Sephadex G50 chromatography of rat pancreatic extracts, the major peak of GLP-1-like immunoreactivity was eluted at the position of synthetic GLP-1 and a minor peak at the 10-kDa position which refers to the major proglucagon fragment (16). The molar ratio of GLP-1-like immunoreactivity to IRG integrated from the elution profile was 0.12. Serial sections immunostained using the peroxidase-antiperoxidase method revealed that GLP-1-like immunoreactivity coexists with IRG in cells located in the marginal zone of the rat pancreatic islets. The levels of GLP-1-like immunoreactivity in the effluent from the isolated perfused rat pancreas were increased by 20 mM arginine in the biphasic pattern synchronously with an increase in IRG levels. The total amounts of GLP-1-like immunoreactivity and IRG released by arginine infusion for 20 min were 18.2±6.1 pmol and 16.8±6.6 pmol, respectively. Thus, the extisence and release of the GLP-1-like immunoreactivity in the rat pancreas were confirmed. However, the reason for the lesser amount of GLP-1-like immunoreactivity compared with IRG in the pancreas should be elucidated.