N alpha-Methylhistamine: association with Helicobacter pylori infection inhumans and effects on gastric acid secretion

Infection with the bacterium Helicobacter pylori is associated with altered gastric acid secretion and gastrointestinal disease. Recent work has sugge sted that N alpha -methylhistamine, produced by the bacterium and acting on histamine receptors in gastric tissue, might be involved. Gastric juice an d tissue biopsies from infected patients have been analysed for the presenc e of N alpha -methylhistamine using a specific and sensitive assay based on gas chromatography mass spectrometry. N alpha -Methylhistamine was detecte d in five of seven samples of gastric juice from infected patients (5-180 p mol/ml) but was absent in nine uninfected subjects. The compound was not fo und in fundic and antral biopsies from both subject groups. Helicobacter py lori, cultured on agar and in broth with and without added histamine, was f ound to to produce detectable levels of N alpha -methylhistamine. Instillat ion of this compound at 10(-5) mol/l into the gastric lumen produced a sign ificant increase in acid secretion in vivo while plasma gastrin concentrati on remained unchanged. N alpha -Methylhistamine in gastric juice appears th erefore to be associated with infection, although this product is not gener ated directly by the bacterium. The concentrations found are below those re quired to affect acid secretion or gastrin production in vivo, although hig her local concentrations may exist around a site of infection. (C) 2000 Els evier Science B.V. All rights reserved.