Neural control of the canine pylorus.

After atropine administration the anesthetized dog exhibits significant spontaneous pyloric contractile activity and an inhibition-relaxation response upon electrical vagal stimulation. This inhibition-relaxation response was completely blocked by tetrodotoxin administration and by transection of the intraabdominal vagal nerves. In addition, tetrodotoxin administration caused a dramatic increase in spontaneous pyloric motor activity. The histaminergic receptor antagonists diphenhydramine and cimetidine did not block the inhibition-relaxation response. The octapeptide of cholecystokinin (CCK-OP) caused a dose-dependent increase in antral and pyloric motor activity which was significantly decreased by atropine administration. Therefore, histamine and CCK do not appear to play a significant role in the vagally mediated inhibition-relaxation response of the canine pylorus or in the atropine-resistant spontaneous pyloric motor activity.