Involvement of serotonergic mechanisms in the disruption of ovine duodenal migrating myoelectric complex cycles by duodenal acidification.

Infusions of 1 and 4 mmol of HCl (pH 2.0) into the duodenal bulb of conscious sheep, within 30% of the period of the migrating myoelectric complex (MMC) cycle, induced aborally propagated premature phases of regular spiking activity (RSA) on the proximal duodenum. A transient inhibition of reticular contractions and a shortening of the period of subsequent duodenal MMC cycles were obtained with infusions of 4 mmol of HCl but not with infusions of 1 mmol. When the animals were pretreated with the 5-hydrotryptamine (5-HT) antagonists, ritanserin (0.2 mg/kg) and metergoline (0.5 mg/kg), 15 min before duodenal infusions of 4 mmol of HCl, premature RSAs and inhibition of reticular contractions were still elicited, but shortening of the subsequent duodenal MMC cycles did not occur. It is concluded that the shortening of duodenal MMC cycles induced by duodenal infusions of 4 mmol of HCl involved a serotonergic mechanism incorporating 5-HT2 receptors. The premature duodenal RSA and inhibition of reticular motility also elicited by these infusions appeared to be independent of this serotonergic system.