Interdigestive motor activity in health and disease

Interdigestive contractile activity in the gastrointestinal tract was measured in dogs and humans. During the interdigestive state, it was found that in healthy dogs and humans, cyclically-recurring strong contractions occurred in the stomach at approximately 100 min intervals and migrated through the small bowel in a caudal direction. The interdigestive contractions consist of three phases, phase I being quiescent while phases II and III are contractile. Phase II contractions resemble those in the digestive state and therefore mix the contents, and phase III contractions are strong in contractile force and consequently squeeze and expel the contents in a caudal direction. Intraduodenal pH changes were studied together with motor activity and it was found that intraduodenal pH remained at a slightly alkaline level during the interdigestive state in the dog; however, in human studies, it was revealed that intraduodenal pH drops below pH 7.0 only during the phase II period. These characteristic contractile changes in the interdigestive state are controlled at least in part by the cyclic increase in motilin concentration in the plasma, but it is not known what regulates the cyclic release of motilin during the interdigestive state. Feeding promptly eliminates changes in the plasma motilin concentration. It is not known whether other gut hormones are involved in the regulation of these specific motor changes in the interdigestive state. One of the typical disorders in motor activity was found in duodenal ulcer. In duodenal ulcer patients, the most characteristic difference from normal subjects was that the duration of phase II activity was significantly prolonged and intraduodenal pH fluctuated widely and intensely during the period. Hypersecretion of acid is well known to be the specific feature of this disease. However, the present study clearly indicates that spontaneous acid secretion per se or vagally induced acid secretion during phase II disturbs the interdigestive motor cycle and, in consequence, leads to the development of ulcers due to the fact that acid contents alone are continuously mixed in the stomach over the prolonged period of phase II activity. These findings lead us to a better understanding of the true pathogenesis of this disease as well as effective treatment of patients from a radical as well as symptomatic standpoint.