Non-neuronal dopamine in the gastrointestinal system

1. Dopamine (DA) is a protective agent in the gastrointestinal (GI) tract in both rats and humans. Therefore, we have studied the site of DA production in rat and human GI tract using a variety of techniques, including immunocytochemistry (ICC), in situ hybridization histochemistry, reverse transcription-polymerase chain reaction, HPLC, western blotting and immunoelectron microscopy. 2. We found very high concentrations of DA that persisted after chemical sympathectomy (CS) in the gastric juice, the stomach mucosa and in the pancreas. Both the stomach mucosa and the pancreas also had tyrosine hydroxylase (TH) activity, most of which remained after CS. Double-labelling ICC showed that acid-producing parietal cells and the exocrine pancreas must also be capable of producing DA. 3. We isolated rat stomach parietal cells by cell fractionation and found that both DA and TH activity are present in isolated (denervated) parietal cells. These cells also have other features of aminergic cells: they are immuno- (and mRNA) positive for the DA plasma membrane transporter and vesicular monoamine transporter(s). In both gastric and duodenal mucosa, we demonstrated the presence of significant amounts of the D5 receptor that could serve as a target for locally produced DA. 4. Because DA, its biosynthetic enzymes and its transporters are also found in parietal cells in the human stomach, a mucosal protective system involving DA could be important clinically.