Pyloric contribution to antroduodenal resistance to flow in the conscious dog

We have developed a pneumatic resistometer to monitor antroduodenal resistance to flow for prolonged periods of time in conscious dogs. To investigate the specific contribution of the pylorus to antroduodenal resistance we compared resistance during fasting in four control dogs and in four dogs with extramucosal pyloric myotomy (1.5 cm long). After pyloric myotomy, as in controls, resistance to flow changed cyclically, being lowest during phase I and highest during phase III of the interdigestive motor cycle. Pyloric myotomy decreased resistance during phase III. Atropine (0.1 mg X kg-1 X h-1) administered during motor quiescence (phase I) reduced resistance in the control group (P less than 0.05) but not in myotomized animals. Bethanechol (0.2 mg X kg-1 X h-1) significantly increased resistance in both groups (P less than 0.05). We conclude that antroduodenal resistance to flow is related to cyclic interdigestive motility. The pylorus is the predominant determinant of antroduodenal resistance during motor quiescence, but its contribution diminishes markedly during motor activity.