[Motility of the small intestine: organization, regulation and functions. 15 years' research on migrating complexes]

The motility pattern of the small intestine has been widely studied over the past fifteen years since a cyclically recurring and distally migrating sequence of myoelectric and motor events was first discovered. Myoelectric or motor migrating complexes (MMC) are composed of 3 main consecutive phases: quiescence, irregular spiking activity and regular spiking activity. Though specific characteristics have been recorded, this sequence seems to be a common pattern in several species of mammals, despite wide differences in digestive anatomy and physiology and very different food habits. Moreover, the basic pattern has been observed to be able to adapt to the mode of feeding and the food composition. Usually, MMC are initiated on the duodenum, but they may be initiated at any level from wandering sources. The anatomical integrity of the intestinal wall is necessary to regular proximodistal migration of the full sequence. Through the cholinergic network of the plexuses, the intrinsic nervous system plays a determinant role in controlling both the initiation and the migration of MMC. The cyclic recurrence of the full sequence, which seems to be a property of the intrinsic plexuses, can be explained by analogy with relaxation oscillators. Nevertheless, the extrinsic nervous system also plays a role, mainly by modulating the duration and intensity of the irregular spiking activity phase. Such a modulation supports the adaptive changes of MMC to feeding. The significance of several hormones and regulatory peptides has also been considered, as some of them cyclically vary in phase with MMC and, as exogenous peptides, they may affect MMC. However, none of these substances plays any determinant role; they rather serve as feedback regulations coordinating small intestine motility with gastric function and pancreatic and biliary secretion, thus giving rise to the so-called secretory component of MMC. The secretions show a cyclic pattern parallel to the MMC pattern, resulting in a cyclic variation of the pH of the duodenal contents. Moreover, it now appears that nervous and humoral controls of MMC should not be distinguished. An overall view of the whole control system is even more complicated due to the possible role of the central nervous system and to the ubiquity of several peptides of the brain-gut axis. In spite of extensive data on these mechanisms, there are still several gaps in our knowledge. But the MMC pattern and its related functions obviously support the coordination of the sequential events involved in digestion.(ABSTRACT TRUNCATED AT 400 WORDS)