Contractile mechanisms of canine colonic propulsion.

We investigated the contractile mechanisms of propulsion in the dog colon. "Propagation index" indicating caudad or orad propagation of contractile states exhibited the strongest correlation with transit during both the fasting and the postprandial states. Other parameters, such as total duration of contractile states and area under contractions, also contributed to transit, but to a lesser degree. All parameters exhibited a stronger correlation with transit during the fasting than during the postprandial state. During the fasting state, the transit rate was faster in the proximal than in the middle colon. The transit rate was linear through the proximal and the middle colon during the postprandial state. In contrast to the phasic contractions and the contractile states, the giant migrating contractions were ultrapropulsive. We conclude that the propagation of contractile states in the colon is a major factor in the slow net distal propulsion of colonic contents. The individual phasic contractions may mainly produce mixing and agitation of colonic contents. Giant migrating contractions rapidly propel colonic contents over long distances.