Histamine type 2 receptor (H2R)

The **histamine type 2 receptor** (H2R) is a member of the G protein-coupled receptor superfamily. It is primarily known for mediating the effects of histamine in stimulating gastric acid secretion by parietal cells in the stomach, making it a classic target for the treatment of gastric and duodenal ulcers, GERD, and related disorders. H2R is also expressed throughout the gastrointestinal tract, the heart, vasculature, immune cells, and various regions of the central nervous system, where it participates in regulating motility, secretion, cell growth, and neurotransmission. H2 antagonists (famotidine, ranitidine, cimetidine, nizatidine) are widely used, both by prescription and over the counter, to decrease gastric acid secretion. Additionally, H2R has been explored as a therapeutic target in CNS disorders such as schizophrenia and in the context of heart failure. The receptor primarily signals through Gs proteins, activating adenylate cyclase and increasing cAMP, but may also engage phosphoinositide and protein kinase C pathways. Structural studies show that ligand binding and G protein coupling involve distinct molecular features, supporting rational drug design. Key functional and safety considerations include tolerance with prolonged antagonist use, central and peripheral side effects, and clinically relevant drug-drug interactions

Other names

Gastric receptor IHH2RHRH2

Competitive inhibition of histamine binding at the H2 receptor (antagonists/blockers) Decreased intracellular cAMP levels in gastric parietal cells, leading to reduced gastric acid secretion (antagonists) Agonists stimulate cAMP production via Gs-protein coupling, promoting gastric acid secretion Some antagonists may also modulate other neurotransmitter systems or receptor internalization/desensitization