Novel autonomic neurotransmitters and upper gastrointestinal function.

The evidence for, and possible roles of, inhibitory and excitatory non-adrenergic, non-cholinergic (NANC) nerves supplying smooth muscle, and the effects of putative transmitter candidates are considered for each of three main regions of the upper gastrointestinal tract: (A) the smooth muscle portion of the oesophagus and the oesophagogastric junction, (B) the stomach (fundus, body and antrum) and gastroduodenal junction and (C) the biliary tract and choledochoduodenal junction. The major points from human tissues are as follows: 1. Inhibitory (NANCI) nerves appear to be present in the muscularis externa of oesophagus, stomach and duodenum, with greater density in the circular than in the longitudinal muscle. 2. NANCI nerves are present in high density at the oesophagogastric and choledochoduodenal junctions. They may also be present at the gastroduodenal junction. The gall-bladder may have a very sparse NANCI innervation. 3. Excitatory (NANCE) nerves appear to be present throughout the upper gastrointestinal tract. 4. Many candidates need at present to be considered for the role of NANCE transmitter(s) in the human upper gastrointestinal tract but substance P still seems a likely contender for this role. 5. Fewer candidates are at present generally available for the role of NANCI transmitter(s), with VIP and ATP being leading contenders. However, in the human upper gastrointestinal tract the evidence for ATP is not good, and VIP still remains the favourite candidate except in the gall-bladder, where its role remains to be elucidated.