Background/aims: In the gastric mucosa of Helicobacter pylori-infected subjects, we previously detected N alpha-methyl histamine (N alpha-MeHA), a minor catabolite of histamine and a potent agonist of histamine H3 receptors. The origin of N alpha-MeHA and its effects on gastric histamine and somatostatin in infected subjects were investigated.
Methods: Ten noninfected patients and 13 patients with intense colonization were compared. N alpha-MeHA content and its synthetic enzyme activity, N alpha-histamine methyltransferase, binding of [3H]N alpha-MeHA, histamine and somatostatin contents, and histidine decarboxylase activity were assayed in antral and fundic biopsy specimens and in cultured H. pylori strains.
Results: Gastric histamine and somatostatin contents as well as histidine decarboxylase activity were decreased in infected patients and were restored to normal after antimicrobial treatment. Both N alpha-MeHA and N alpha-histamine methyltransferase activity were present in the mucosa of infected patients and in cultured strains and were very low in noninfected patients or after eradication of H. pylori. [3H]N alpha-MeHA bound to gastric mucosa but not to cultured strains. The [3H]N alpha-MeHA specific binding sites were characterized as H3 receptors. The amount of bound [3H]N alpha-MeHA seemed correlated positively with somatostatin content and histidine decarboxylase activity and negatively with N alpha-MeHA content and N alpha-histamine methyltransferase activity.
Conclusions: H. pylori is the main source of gastric N alpha-MeHA that may lower histidine decarboxylase activity and somatostatin content through H3 receptors.