Intragastric capsaicin stimulates motility of upper gut and proximal colon via distinct pathways in conscious dogs

The aim of the present study was to investigate the effect and mechanism of action of intragastric and intraduodenal capsaicin on gastrointestinal motility. Five mongrel dOgs were equipped with eight strain gauge force transducers on the stomach, small intestine, and proximal colon. In the interdigestive state, capsaicin was administered into the gastric or duodenal lumen. The effects of atropine, hexamethonium, ondansetron, and FK888 on capsaicin-induced contractions were studied. Intragastric capsaicin induced contractions within 15 min in the gastric antrum, duodenum, proximal jejunum, and proximal colon. These stimulatory effects were inhibited by atropine at all sites; by hexamethonium in the small intestine and colon; by ondansetron in the antrum, duodenum, and colon; and by FK888 in the antrum and colon, respectively. Intraduodenal capsaicin had no effect on contractility. Stimulation of afferent fibers by capsaicin in the stomach but not in the duodenum augments contractile activity in local and distant regions of the gut via distinct pathways.