Colocalization of glucagon-like peptide and glucagon immunoreactivities in pancreatic islets and intestine of salmonids.

Pancreatic islets of salmon contain at least two peptides of the glucagon family: 29-amino acid glucagon and 31-amino acid glucagon-like peptide (GLP). Both peptides were recently isolated from the pancreatic islets of coho salmon and sequenced (Plisetskaya et al. 1986). Antibodies generated against these two peptides and against human glucagon were used as immunocytochemical probes to investigate whether glucagon and GLP are processed in the same, or in different cell types in the pancreatic islets and the gut of salmon. Two salmonid species, rainbow trout and coho salmon, were studied. All islet A-cells in the two species were immunoreactive toward both anti-salmon (s)-glucagon and anti-s-GLP. Similar colocalization of glucagon and GLP immunoreactivites was found in open-type endocrine cells in mucosae of the small intestine (including the pyloric coecae) and the large intestine close to the vent of rainbow trout. None of the antibodies stained mucosal cells of the body of the stomach. These results suggest that in the pancreas and the gut of salmonid fish the same cells produce both glucagon and GLP. These peptides are most likely the products of a single gene coding for the preproglucagon sequence.