BACKGROUND & AIMS: The aim of the present study was to determine the effect of intraileal administration of capsaicin on gastrointestinal motility. METHODS: Mongrel dogs equipped with strain gauge force transducers on the stomach, small intestine, and colon were used. We studied the effects of intraileal capsaicin on gastrointestinal contractions with or without pharmacologic antagonists. The effects of capsaicin administration into the lumen of innervated and extrinsically denervated ileal Thiry loops were also studied. RESULTS: Intraileal capsaicin dose dependently inhibited postprandial contractions at all sites and interdigestive contractions in the upper gastrointestinal tract. Intraileal capsaicin-induced inhibition of gastrointestinal contractions was partially reversed by a nitric oxide (NO) synthase inhibitor, a 5 hydroxytryptamine-3 receptor antagonist (5-HT(3)), and an opiate antagonist. Administration of capsaicin into the innervated ileal Thiry loop had inhibitory effects on gastrointestinal contractions, but gastrointesinal motor activity was not affected by capsaicin administered into the extrinsically denervated Thiry loop. CONCLUSIONS: Stimulation of ileal afferent fibers by capsaicin inhibits gastrointestinal contractions via an extrinsic neural reflex.
BACKGROUND & AIMS: The aim of the present study was to determine the effect of intraileal administration of capsaicin on gastrointestinal motility. METHODS: Mongrel dogs equipped with strain gauge force transducers on the stomach, small intestine, and colon were used. We studied the effects of intraileal capsaicin on gastrointestinal contractions with or without pharmacologic antagonists. The effects of capsaicin administration into the lumen of innervated and extrinsically denervated ileal Thiry loops were also studied. RESULTS: Intraileal capsaicin dose dependently inhibited postprandial contractions at all sites and interdigestive contractions in the upper gastrointestinal tract. Intraileal capsaicin-induced inhibition of gastrointestinal contractions was partially reversed by a nitric oxide (NO) synthase inhibitor, a 5 hydroxytryptamine-3 receptor antagonist (5-HT(3)), and an opiate antagonist. Administration of capsaicin into the innervated ileal Thiry loop had inhibitory effects on gastrointestinal contractions, but gastrointesinal motor activity was not affected by capsaicin administered into the extrinsically denervated Thiry loop. CONCLUSIONS: Stimulation of ileal afferent fibers by capsaicin inhibits gastrointestinal contractions via an extrinsic neural reflex.