Initiation of migrating myoelectric complex in sheep by duodenal acidification and hyperosmolarity: role of vagus nerves.

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Abstract
Gastrointestinal motility was studied in conscious sheep by X-radiography and by electromyography from chronically implanted electrodes before and after total thoracic vagotomy. Duodenal infusion of 0.5-3 mmol HCl (0.035-0.1 M-HCl) induced premature duodenal regular spiking activity (RSA) within 1-7 min in 15 of 17 sheep studied when infused at 20 min after a natural RSA. There was no correlation between abomasal pH and any phase of the migrating myoelectric complex (MMC). Duodenal alkalinization by infusion of 0.3 M-Tris buffer (pH 10.2) or 0.1 M-NaHCO3 had no influence on the occurrence of the MMC. The vagus nerves contribute to the regulation of the frequency and propagation of the MMC in sheep: duodenal acidification is not essential nor is it the normal stimulus for initiation of RSA, but duodenal infusion of HCl or hyperosmolar NaCl can initiate a premature duodenal RSA via the vagus nerves.