BACKGROUND/AIMS: Intragastric acidification at pH 1.0 strongly inhibits phase III contractions in the dog, but this mechanism is not well known. We studied the mechanism in conscious dogs. METHODS: Vagally denervated and innervated gastric pouch dogs were prepared. Force transducers were chronically implanted on the serosa of the pouch, main stomach, and mid-duodenum. The pH of the perfusate was monitored. RESULTS: Administration of histamine (40 micrograms.kg-1.h-1 intravenously [i.v.]) and instillation of acidic saline at pH 1.0, but not pH 2.0, into the main stomach strongly inhibited the motilin-induced (0.1 microgram/kg i.v.) phase III activity in the main stomach and the innervated pouch but did not influence contractions in the extrinsically denervated pouch. Famotidine completely reversed the histamine-induced inhibition of phase III in the main stomach and Pavlov pouch. Acidification of the pouch itself or duodenum at pH 1.0 did not affect contractions in the main stomach and pouch of either type. CONCLUSIONS: The mechanism of inhibition of motilin-induced phase III activity by acid in the stomach involves the intact vagovagal reflex, but sympathetic participation is not completely ruled out. The inhibition of motilin-induced phase III activity may originate in the antral mucosa of the stomach.
BACKGROUND/AIMS: Intragastric acidification at pH 1.0 strongly inhibits phase III contractions in the dog, but this mechanism is not well known. We studied the mechanism in conscious dogs. METHODS: Vagally denervated and innervated gastric pouch dogs were prepared. Force transducers were chronically implanted on the serosa of the pouch, main stomach, and mid-duodenum. The pH of the perfusate was monitored. RESULTS: Administration of histamine (40 micrograms.kg-1.h-1 intravenously [i.v.]) and instillation of acidic saline at pH 1.0, but not pH 2.0, into the main stomach strongly inhibited the motilin-induced (0.1 microgram/kg i.v.) phase III activity in the main stomach and the innervated pouch but did not influence contractions in the extrinsically denervated pouch. Famotidine completely reversed the histamine-induced inhibition of phase III in the main stomach and Pavlov pouch. Acidification of the pouch itself or duodenum at pH 1.0 did not affect contractions in the main stomach and pouch of either type. CONCLUSIONS: The mechanism of inhibition of motilin-induced phase III activity by acid in the stomach involves the intact vagovagal reflex, but sympathetic participation is not completely ruled out. The inhibition of motilin-induced phase III activity may originate in the antral mucosa of the stomach.