Enteric mechanisms of initiation of migrating myoelectric complexes in dogs.

The enteric mechanisms governing initiation of migrating myoelectric complexes were studied in 6 conscious dogs, each implanted with a set of 12 bipolar electrodes on the small intestine. The small intestine was transected and reanastomosed at three sites to give four isolated segments of equal length. Each segment had three implanted electrodes. All four isolated segments generated migrating myoelectric complexes which were, initially, totally independent of each other in time. The most proximal segment had the longest mean migrating myoelectric complex time period (106.2 +/- 10.1 SEM min) and the second segment had the shortest mean migrating myoelectric complex time period (66.8 +/- 6.7 SEM min). Distal to the second segment, the mean migrating myoelectric complex time period increased progressively (83.1 +/- 11.2 SEM min and 95.8 +/- 7.6 SEM min, respectively). Isolation of the small intestine into segments did not significantly change migrating myoelectric complex propagation characteristics such as velocity and direction of propagation within each segment. The mean duration of phase 3 activity was not affected in the first segment but increased significantly in the distal three segments (p less than 0.05). The propagation of migrating myoelectric complexes across the sites of transection and reanastomosis started recovering 45-60 days after surgery and recovered fully by 98-108 days. The study findings show that enteric mechanisms control the initiation of migrating myoelectric complexes. Each small segment of the small intestine is capable of initiating migrating myoelectric complexes of its own and behaves as a relaxation oscillator. In the intact small intestine, regional migrating myoelectric complex oscillators are coupled by the intrinsic neurons so that the proximal oscillators drive the distal oscillators. Recovery of migrating myoelectric complex propagation across sites of transection and reanastomosis suggest that intrinsic nerves regenerate after transection.