Glucagon-like peptide-1 is co-localized with neurotensin in the chicken ileum

Glucagon-like peptide (GLP)-1 and neurotensin (NT) are distributed throughout the chicken ileum. Here, we attempt to determine if GLP-1 and NT co-localize in the chicken ileum by using immunofluorescence, immunocytochemistry and in situ hybridization techniques. Three types of enteroendocrine cells, GLP-1+/NT+, GLP-1+/NT− and GLP-1−/NT+ cells, were detected in the mucosal epithelium by the double immunofluorescence method. The ratio of GLP-1+/NT+ cells at the crypts in the distal ileum was significantly higher than that in the proximal ileum. The ratios of the three cell types were similar along the crypt–villous axis in the proximal ileum but the percentage of GLP-1+/NT+ cells significantly decreased at the middle part of villi relative to crypts and the bottom part of villi in the distal ileum. Enteroendocrine cells that were immunoreactive to both GLP-1 and NT peptides and showed both proglucagon and NT precursor mRNA signals were found in the crypts of the distal ileum but not in the villous epithelium. The results from performing an immunocytochemical method with colloidal gold indicated that the GLP-1 content within GLP-1+/NT+ cell secretory granules decreased stepwise from the crypt to the middle part of the villus but the NT content in these granules increased in this direction. These findings reveal that the cells producing both GLP-1 and NT are mainly localized in the crypts of the chicken ileum but these endocrine cells specialize in NT-producing cells at the villous epithelium of the distal ileum.