Histamine H₂ receptor (H₂ receptor (sometimes abbreviated as H2R))

The histamine H₂ receptor is a transmembrane G protein–coupled receptor primarily located on parietal cells of the stomach, where it mediates the stimulatory effects of histamine on gastric acid secretion. It is also present in several other tissues, including vascular smooth muscle, neutrophils, cardiac tissue, and some brain regions. Activation of this receptor initiates a signaling cascade via Gs proteins that activate adenylate cyclase and increase cyclic AMP, ultimately stimulating protein kinase A and promoting gastric acid release. The H₂ receptor is a central therapeutic target for gastric acid–related disorders such as peptic ulcers and GERD, with antagonists (H₂ blockers) like cimetidine, ranitidine, famotidine, and nizatidine used to suppress acid secretion. The receptor is also involved in other functions such as immune modulation and smooth muscle relaxation. Safety concerns for pharmacological targeting include rare hepatic toxicity and drug–drug interactions.

Other names

H2 receptorH2RHistamine receptor H2HRH2

Competitive antagonism at the histamine H₂ receptor (prevents histamine-mediated stimulation of gastric acid secretion). Inhibits activation of adenylate cyclase and subsequent cAMP production in parietal cells (decreases activation of protein kinase A, reducing acid secretion).