Aspects on luminal nitric oxide in relation to oesophageal acid exposure and mucosal integrity

Sammanfattning: Nitric oxide (NO) exerts important neuromuscular control of the oesophagus, but little is known about the sources and effects of the NO present in the distal oesophageal lumen. These questions were presently addressed in both human and animal experiments. An increase in [NO] was observed in healthy volunteers on oesophageal acid exposure which was dependent on both nitrate intake and the presence of saliva. In healthy volunteers, treated and untreated patients with gastro-oesophageal reflux disease (GORD), the basal [NO] increased stepwise by disease state. Acid exposure gave rise to a substantial increase in [NO], most marked in GORD patients, despite salivary deviation and PPI treatment. In a ferret model dividing the oesophagus to exclude saliva and gastric refluxate, a significant percentual increase in luminal NO was still elicited by acid exposure. This reaction was blocked by the NO-synthase inhibitors L-NAME and 1400w. A randomised and blinded histological evaluation of chronic and acute acid damage to the human oesophageal epithelium verified that an adequate noxious stimulus had been given in the human model. Further, it revealed that markers associated with disease state were; an increase in the thickness of the basal layers, the length of the papillae and possibly, dilatation of intercellular spaces (DIS). Markers associated with acute acid challenge were ballooning of superficial layers, superficial densification and possibly the occurrence of granulocyte infiltration. NO synthase (iNOS) was found by immunohistochemistry in the epithelia of both humans and ferrets, implying preconditions for an enzymatic epithelial NO production. In humans the isoform was further confirmed by Western blot and rtPCR technique. However, an increase of iNOS immunoreactivity on acid exposure was found in ferrets only. In ferrets, iNOS blockers led to a steeper rise in PD and a tendency to an earlier decline towards nadir, which might be taken as a weak suggestion of an influence of NO on ion fluxes and epithelial integrity. This would be in accordance with the finding that the healthy volunteer group - which had a lower NO increase on acid exposure showed a more pronounced increase in DIS on acute exposure. A correlation was found in humans between a deep nadir on PD and a high degree of DIS which suggest an association between DIS and mucosal integrity. Changes in luminal [NO], as modified by dietary/salivary nitrite/nitrate contents, had no influence on oesophageal neuromuscular functions (motility, sensitivity, LOS functions) nor on oesophageal or gastric 24 hour acidity. Blood flow was slightly lower amongst reflux patients but did not react to acute changes in acid exposure or nitric oxide. In conclusion, oesophageal luminal NO has two sources, chemical production from dietary nitrate and endogenous production via iNOS. Local nitric oxide formation is particularly pronounced in gastro-esophageal reflux disease. Intraluminal NO did not affect oesophageal blood flow, motility, gastric or oesophageal acid exposure. No substantial proof of NO effects on epithelial integrity as expressed by PD and histology was found. The role of luminal NO in GORD has yet to be determined.