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

Abstract

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.

Influence of enteric helminths on the distribution of intestinal endocrine cells belonging to the diffuse endocrine system in brown trout, Salmo trutta L.

“…The occurrence of cells immunopositive to anti-glucagon serum was reported in the intestine of rainbow trout, Oncorhynchus mykiss Walbaum (Holmgren et al 1982;Beorlegui et al 1992). However, no positive reactions were found in the stomach or the nervous system of this species (Holmgren et al 1982;Nozaki, Miyata, Oota, Gorbman & Plisetskaya 1988;Beorlegui et al 1992).…”

Immunohistochemical study of the gastrointestinal endocrine cells in the Korean aucha perch

“…It is well documented that the distribution and frequency of glucagon‐IR cells in the alimentary tract vary with fish species (Al‐Mahrouki & Youson, 1998). They were generally detected in the proximal parts of the gut of some species of teleosts (Nozaki et al ., 1988; Conlon & Falkmer, 1989) and cartilaginous fishes (Faraldi et al ., 1988). In addition, the ontogeny of glucagon‐IR cells was monitored in the GI tract of turbot (Reinecke et al ., 1997) and sea bream Sparus aurata L. (Sarasquete et al ., 1993).…”

Physiology of fish endocrine pancreas

“…We have found that glucagon and glucagon-like peptide are expressed within the same islet cells (Nozaki et al 1988b), while SST-14 and SST-25, the products of different genes, are expressed in different cells (Nozaki et al 1988a). Even more puzzling was the discovery that cells expressing SST-14 are located adjacent to insulin immunoreactive cells, while cells expressing SST-25 are associated topographically with glucagon/GLP-positive cells (Nozaki et al 1988a).…”