Initiation of duodenal acid-induced motor complexes

The contractile activity associated with spontaneous migrating myoelectric complexes was recorded from the antrum and duodenum of 11 subjects; complexes always consisted of gastric and duodenal components, each followed by a period of total inhibition of activity. Fifty milliliters of the following solutions were infused into the duodenum at 5 ml/min; 0.9% saline, 100 mM Tris buffer (pH 8.0), and 100 mM HCl. Only HCl initiated contractions resembling the duodenal phase of a migrating myoelectric complex; maximal gastric activity never preceded acid-induced duodenal activity. Acid-induced complexes did not differ from spontaneous complexes in their contraction rate, velocity of propagation, or period of postcomplex inhibition; they were significantly shorter. The occurrence of an acid-induced or spontaneous complex each inhibited the occurrence of the other for at least 26 min. Of 5 subjects receiving 50 ml of 10, 20, and 50 mM HCl at 5 ml/min, 3 responded to 50 mM HCl and 2 to 20 mM HCl with a complex; an average of 0.33 mmol ± 0.10 (SE) of HCl initiated a complex. Duodenal infusion of 50 ml of 100 mM HCl within 3 min caused maximal duodenal activity, which began simultaneously at all recording sites, did not propagate, and had no inhibition following. Infusion of 50 ml of 100 mM HCl into the stomach over 10 min increased duodenal contractile activity for the 10 min after the infusion, but no complexes were initiated. In 4 subjects, acid-induced complexes (100 mM HCl in 10 min) were prevented by intravenous atropine 20 μg/kg. Infusion of synthetic 13-leucine motilin (1, 10, and 100 μg) into the duodenum in 6 subjects did not affect gastroduodenal motility. Thus, intraduodenal HCl can induce contractile activity resembling the duodenal phase of a migrating complex, mediated mainly through postganglionic cholinergic neurons. A bolus of HCl emptied into the duodenum by the antral phase of a complex may be one means of propagating the gastric phase of a complex into the duodenum.