Mechanisms coordinating gastric and small intestinal MMC: role of extrinsic innervation rather than motilin

Abstract

We have investigated the role of vagal and efferent adrenergic innervation coordinating the gastric and small intestinal migrating motor complexes (MMCs) after removal of the pylorus, duodenum, and upper jejunum in three dogs. The cervical vagus nerves were previously isolated in bilateral skin loops to permit reversible cooling blockade of the vagi. Pharmacological alpha- and beta-receptor blockade was accomplished by bolus intravenous injection of phentolamine and propranolol followed by intravenous infusion of the combined drugs. Gastric and upper jejunal MMC-like activity was initially absent after bowel resection but reappeared after 1-4 mo with the gastric and jejunal MMC-like activities coordinated as if the jejunum were the duodenum. Motilin peaks were absent. All gastric contractions were abolished by vagal blockade. Pharmacological adrenergic blockade immediately induced an intense burst of contractile and electrical activity in the stomach, which propagated to the distal ileum. This phase III-like burst was followed by ongoing intermittent bursts of contractile and electrical activity in the stomach and small intestine, lasting throughout the blockade, without further MMC-like activity. Vagal cooling blockade in combination with adrenergic blockade did not restore gastric MMC-like activity but abolished or decreased the number of gastric contractions, with the reappearance of the small intestinal MMC. Atropine boluses abolished all control and adrenergic blockade-induced stomach and small intestinal contractile and electrical activity. In conclusion, after duodenectomy, the gastric MMC-like activity that is reestablished and is coordinated with the small intestinal MMC is vagally dependent and cholinergic, but its cyclical nature requires adrenergic efferent pathways. Under these circumstances, coordination of the gastric and jejunal MMCs appears to require extrinsic innervation.