Vagal Influences on the Phasic and Tonic Components of the Motility of the Ovine Stomach and Gastroduodenal Area

Abstract

Both the phasic and tonic components of gastric motility including the gastroduodenal junction were recorded after section or cooling blockade of the vagus nerves in conscious sheep. The phasic contractile activity was monitored using electromyography, strain gauges, and intraluminal manometry. The changes in the tone of the stomach (abomasum) were assessed by an electronic barostat. The cyclical contractions of the reticulorumen ceased immediately after bilateral vagotomy, whereas the activity of the antral part of the abomasum was strongly enhanced. Two weeks after vagotomy, the abomasal hypermotility persisted while reticuloruminal movements developed from a local nervous network. Vagal cooling at 5°C of one of the vagus nerves after section of the contralateral vagus similarly inhibited reticuloruminal contractions in contrast to the occurrence of abomasal hypermotility. During vagal cooling, both the abomasal and pyloric tone were lowered. We conclude that vagal cooling impairs excitatory input to the reticulorumen and inhibitory input to the gastroduodenal junction. The decreased smooth muscle tone at the abomasal and pylorus levels during vagal cooling suggests that vagal stimulatory influences are abated.