Generation of phases I and II of migrating myoelectric complex in the dog

The mechanisms of generation of most of the phases of the migrating myoelectric complex (MMC) are unclear. Except for phase III activity, this issue has not been investigated directly. We have qualitatively examined the relations between different phases of the MMC cycle in the order to provide an objective basis for the formation of theories. Eight dogs of either sex were implanted with 10 bipolar electrodes distributed along the gastrointestinal tract. Myoelectric activity was recorded during the fasted state or after feeding until the return of the MMC cycle. The relations between phase I duration, phase II duration, phase III migration time, and phase III period were examined using simple linear-regression methods. We found that only phase I duration was highly correlated (r = 0.87, P < 0.01) with phase III migration time and that only phase II duration was highly correlated (r = 0.90, P < 0.01) with phase III period. In either the fed or fasted state, phase III activity that began in the midjejunum was accompanied concurrently with phase I activity of the duodenum and upper jejunum, where phase III activity had not occurred. Also, the position of phase III activity in the lower small intestine when phase I activity of the upper small intestine ended was 277 ± 24 cm (83 ± 5% of the small intestinal length) from the pylorus, and the coefficient of variation of this position was significantly smaller (P < 0.01) than that of the other cycle variables. Together these results suggest that only phase III activity migrates and that phase I activity may be controlled by phase III activity at distal sites. In addition, rather than being an integral part of the MMC cycle, phase II activity may represent background activity whose limits are determined by the occurrence of phase III activity.