THE MIGRATING MOTOR COMPLEX - THE MOTOR COMPONENT OF A CHOLINERGIC ENTERIC SECRETOMOTOR PROGRAM

The role of cholinergic nerves in the cyclic activation of interdigest ive motility and secretion was studied in 23 healthy volunteers. Net f luid transport in a distal duodenal segment and the release of pancrea ticobiliary secretions into the duodenal lumen, were measured with a t riple lumen perfusion technique. Interdigestive motor activity was rec orded with a low-compliance pneumohydraulic system, and the transmural potential difference (PD) was measured as an on-line marker of electr ogenic anion secretion. Transport parameters were related to the migra ting motor complex (MMC) in the control situation and after the admini stration of atropine (0.01 mg kg(-1) body wt, i.v.). The early part of the MMC cycle was characterized by low motor activity, low release of bile and pancreatic juice into the duodenal lumen, a slightly lumen p ositive transmural PD, and a non-significant net fluid absorption ('ab sorptive mode'). Under control conditions, motor activity and pancreat icobiliary secretions subsequently increased and there was a shift in net fluid transport and transmural PD in the secretory direction ('sec retory mode'). Furthermore, there was a significant correlation betwee n contraction frequency, a more lumen negative PD, and the magnitude o f net fluid secretion. After the administration of atropine, the secre tory mode was abolished, but there was still a significant correlation between contraction frequency and transmural PD. In conclusion, choli nergic neurones seem to mediate the shift from the absorptive to the s ecretory mode in the human distal duodenum. The antisecretory effect o f atropine may be the result of inhibition of motilin release, reduced activation of tension-sensitive intramural secretory pathways, or blo ckade of cholinergic neurones to the secreting epithelium.