Abstract
In the fasted gastrointestinal (GI) tract, a characteristic cyclical rhythmic migrating motor complex (MMC) occurs in an ultradian rhythm, at 90–120 min time intervals, in many species. However, the underlying mechanism directing this ultradian rhythmic MMC pattern is yet to be completely elucidated. Therefore, this study aimed to identify the possible causes or factors that involve in the occurrence of the fasting gastric contractions by using Suncus murinus a small model animal featuring almost the same rhythmic MMC as that found in humans and dogs. We observed that either intraduodenal infusion of saline at pH 8 evoked the strong gastric contraction or continuously lowering duodenal pH to 3‐evoked gastric phase II‐like and phase III‐like contractions, and both strong contractions were essentially abolished by the intravenous administration of MA 2029 (motilin receptor antagonist) and D‐Lys3‐GHRP6 (ghrelin receptor antagonist) in a vagus‐independent manner. Moreover, we observed that the prostaglandin E2‐alpha (PGE2‐ α) and serotonin type 4 (5HT4) receptors play important roles as intermediate molecules in changes in GI pH and motilin release. These results suggest a clear insight mechanism that change in the duodenal pH to alkaline condition is an essential factor for stimulating the endogenous release of motilin and governs the fasting MMC in a vagus‐independent manner. Finally, we believe that the changes in duodenal pH triggered by flowing gastric acid and the release of duodenal bicarbonate through the involvement of PGE2‐ α and 5HT4 receptor are the key events in the occurrence of the MMC.
Highlights
The term migrating motor complex (MMC) was first defined by Szurszewski (1969) as the result of the recording of a cyclic pattern of intestinal migrating myoelectrical activity in dogs
We examined whether ID changes in pH could affect gastric contractions
We observed that ID infusion of saline at different pH values at a rate of 2.0 mL/ min for 1 min induced gastric contractions in a pHdependent manner (Fig. 1Aa), and that the motility index (MI) of the ID infusion of pH 8 saline with a volume of 2 mL was the maximum, and similar to motilin-induced phase III-like contractions (Fig. 1Ab)
Summary
The term migrating motor complex (MMC) was first defined by Szurszewski (1969) as the result of the recording of a cyclic pattern of intestinal migrating myoelectrical activity in dogs. The stomach and small intestine undergo a temporally coordinated cyclic motor pattern in many monogastric animals (including rodents, dogs, pigs, rabbits, and humans), known as the migrating motor complex (MMC) (Szurszewski 1969; Vantrappen et al 1977). It has been observed that the occurrence of the MMC is regulated in an ultradian rhythmic period of 90–120 min intervals in the gastrointestinal (GI) tract in humans and dogs (Itoh et al 1976; Vantrappen et al 1979a). Whether the occurrence of such ultradian rhythmic patterns of the MMC is found in multiple species during the interdigestive state with a stipulated time interval is a question that remains to be answered
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