Role of histamine H4 receptors in the gastrointestinal tract.

The location and functional role of histamine H4 receptors (H4Rs) in the gastrointestinal tract (GI) is reviewed, with particular reference to their involvement in the regulation of gastric acid secretion, gastric mucosal defense, intestinal motility and secretion, visceral sensitivity, inflammation, immunity and carcinogenesis. H4Rs have been detected in different cell types of the gut, including immune cells, paracrine cells, endocrine cells and neurons; moreover, H4R expression was reported in human colorectal cancer specimens. Functional studies with selective H4R ligands demonstrated protective effects in several experimental models of gastric mucosal damage and intestinal inflammation, suggesting a potential therapeutic role of drugs targeting this new receptor subtype in GI disorders, such as allergic enteropathy, inflammatory bowel disease (IBD), irritable bowel syndrome (IBS) and cancer.