Canine cyclic motor activity of stomach and small bowel: the vagus is not the governor.

The influence of the vagus nerve on gastric cyclic motor activity and small bowel migrating motor complexes is controversial. Diaphragmatic vagesection does not alter their occurrence or periodicity, but cervical vagal cooling inhibits both gastric cyclic motor activity and duodenal phase II activity. We have clarified this contradictory data by reversible vagal cooling at the diaphragm level in 5 dogs implanted with strain gages and bipolar electrodes to record gastric and small intestinal cyclic activities. Circulation of coolant through an implanted convectional jacket surrounding the vagal trunks lowered jacket temperature to 2 degrees-8 degrees C and maintained this temperature for 3-5 h in each experiment. Vagal denervation during cooling was proven at the end of each trial by abolition of intravenous insulin-stimulated gastric contractions, which promptly appeared with warming. More than 90% of gastric motor cycles persisted during vagal cooling. The mean duration of gastric phase III activity was reduced during cooling but the mean period of gastric motor cycles was unchanged. Duodenal phase II and III activities were unchanged and migrated normally through the small bowel. We conclude that the vagus nerve may modulate the duration of gastric phase III activity but does not govern the initiation of gastric cyclic motor activity or the duration, period, and migration of small intestinal migrating myoelectric complexes. These findings concur with those after truncal vagectomy but are different from observations made with cervical vagal cooling.