Mechanism of interdigestive migrating motor complex in conscious dogs

The migrating motor complex (MMC) is well characterized by the appearance of gastrointestinal contractions in the interdigestive state. This study was designed to clarify the mechanisms of gastric MMC (G-MMC) and intestinal MMC (I-MMC) in conscious dogs. Five strain gauge transducers were implanted on the stomach and intestine. To investigate the correlation between luminal 5-HT and phase III contractions, gastric and duodenal juices were collected during the MMC cycle. The 5-HT concentrations in gastric and duodenal juice were measured by HPLC. To investigate whether luminal 5-HT initiates MMC, 5-HT (10(-8)-10(-6) M, 10 ml) was administered into the duodenum 20 min after gastric phase III. To investigate the involvement of 5-HT3 or 5-HT4 receptors in mediating G-MMC and I-MMC, 5-HT3 antagonists (ondansetron) or 5-HT4 antagonists (GR 125,487) were infused for 120 min. Luminal administration of 5-HT (10(-6) M) initiated duodenal phase II followed by G-MMC and I-MMC with a concomitant increased release of plasma motilin. The duodenal 5-HT concentration was significantly increased during phase II (59 +/- A 9 ng/ml) and phase III (251 +/- A 21 ng/ml) compared to that of phase I (29 +/- A 5 ng/ml). On the other hand, the 5-HT content in the stomach was not significantly changed throughout the MMC cycle. Intravenous infusion of motilin (0.3 mu g/kg/h) increased the luminal 5-HT content and induced G-MMC and I-MMC. 5-HT4 antagonists significantly inhibited both G-MMC and I-MMC, while 5-HT3 antagonists inhibited only G-MMC. It is suggested that the MMC cycle is mediated by a positive feedback mechanism via the interaction between motilin and 5-HT.