Local, exendin-(9-39)-insensitive, site of action of GLP-1 in canine ileum

Glucagon-like peptide-1 (GLP-1) modulates glucose levels following a meal, including by inhibition of gastric emptying and intestinal transport. Intra-arterial injection of GLP-1 into the gastric corpus, antrum, or pylorus of anesthetized dogs had no effect on the contractile activity of the resting or neurally activated stomach. GLP-1 injected intra-arterially inhibited intestinal segments when activated by enteric nerve stimulation but not by acetylcholine. Isolated ileum segments were perfused intra-arterially, instrumented with strain gauges to record circular muscle activity and with subserosal electrodes to stimulate enteric nerves. GLP-1 caused concentration-dependent inhibition of nerve-stimulated phasic but not tonic activity. This was absent during TTX-induced activity and partly prevented by N-G-nitro-L-arginine. Exendin-(9-39), the GLP-1 antagonist, had no intrinsic activity and did not affect the actions of GLP-1. Capsaicin mimicked the effects of GLP-1 and may have reduced the effect of subsequent GLP-1. GLP-1 may mediate paracrine action on afferent nerves in the canine ileal mucosa using an unusual receptor.