Adrenergic blockage does not restore the canine gastric migrating motor complex during vagal blockade

Bilateral cervical cooling blockade of the vagi abolishes the gastric migrating motility complex (MMC), except for the pylorus. The present study investigated if this finding is caused by adrenergic inhibition of the stomach via sympathetic nerves entering the vagi below the level of the blockade. Stomach and upper small bowel motor activity was monitored in five chronic dogs whose vagosympathetic nerve trunks were previously isolated in bilateral, cervical skin loops to permit blockade by cooling. Adrenergic blockade was performed by an initial bolus injection of phentolamine (0.3 mg/kg) and propranolol (0.3 mg/kg) followed by a continuous intravenous infusion of the combined drugs at a rate of 1.5 mg.kg-1.h-1 for phentolamine and 0.3 mg.kg-1.h-1 for propranolol. Bilateral cervical vagal blockade abolished the gastric MMC, with persistence of phase III of the MMC in the upper small bowel. During combined vagal and adrenergic blockade, gastric contractions were absent in 4 of the 22 duodenal complexes observed. In the other duodenal complexes, intermittent gastric contractions were associated with all phases of the intestinal MMC, including phase I. At times, this contractile activity was accentuated during phase III but never reached the intensity of activity or showed the typical coordination features of the gastric MMC seen with the vagi intact. Therefore, unopposed adrenergic inhibition of the stomach does not explain the absence of the gastric MMC during vagal cooling blockade. Under normal circumstances, the vagus nerve is the most important pathway for central control of the appearance of the gastric MMC.