Glucagon-like peptide-1 (GLP-1) is a gut peptide with regulatory effects in the gastrointestinal tract by acting at the G protein-coupled receptor, GLP-1R. We investigate the involvement of GLP-1 in intestinal mucosal secretory function. Mucosal preparations from guinea pig ileum were mounted in Ussing flux chambers for measurement of short-current (Isc) as a surrogate for chloride secretion. Expression of GLP-1R was assessed with immunohistochemistry. ELISA was used to study the effects of GLR-1R activation on acetylcholine (ACh) release. Transmural electrical field stimulation (EFS) evoked a typical biphasic increase in Isc. GLP-1 (0.1 nM-1 mM) produced a concentration-dependent reduction in the EFS-evoked biphasic response, suppressed by exendin (9-39) (10 nM), a GLP-1R antagonist. The inhibitory action of GLP-1 was abolished by tetrodoxin (1mM), reduced by scopolamine (1 mM) but it was not affected by hexamethonium (100 mM) or VPAC1 receptor antagonist (1 mM). GLP-1 (10 nM) significantly reduced the amount of ACh release and the effect was almost abolished by pre-treatment with exendin (9-39). In the submucosal plexus, GLP-1R-immunoreactivity (-IR) was expressed in choline acetyltransferase-IR neurons, neuropeptide Y-IR neurons, somatostatin-IR neurons and vasoactive intestinal peptide-IR neurons. These data suggest that GLP-1 is able to modulate chloride secretion by subclasses of neurons in the submucosal plexus of guinea pig small intestine which express the GLP-1R.