Functional activity of murine intestinal mucosal cells is regulated by the glucagon-like peptide-1 receptor

To determine whether the glucagon-like peptide-1 receptor (GLP-1r) plays a role in the regulation of intestinal functional activity, we analyzed the distribution of the GLP-1r in mouse tissues and tested if tissues expressing the receptor respond to exendin-4 and exendin (9-39) amide, a GLP-1r agonist and antagonist respectively. In ileum, Glp1r mRNA level was two fold higher in extracts from epithelial cells than non-epithelial tissues. By immunohistochemistry, the receptor was localized to the mucosal cell layer of villi of ileum and colon, to the myenteric and submucosal plexus and to Paneth cells. Intravenous administration of exendin-4 to CD-1 mice induced expression of the immediate early gene c-fos in mucosal cells but not in cells of the enteric plexuses or in L cells of ileum. The induction of c-fos was inhibited by the voltage-gated sodium channel blocker tetrodotoxin. Exendin-4 also increased c-fos expression in ileal segments in vitro, suggesting that this action of the analog was independent of an extrinsic input. The induction of c-fos expression by exendin-4 was inhibited by exendin (9-39) amide, indicating that the action of exendin-4 was mediated by activation of the receptor. Our findings indicate that the GLP-1r is involved in ileal enterocyte and Paneth cell function, that the GLP-1 analog activates c-fos expression in the absence of an extrinsic input and that some of the actions of the receptor is/are mediated by voltage-gated Na channels.