histamine2

Histamine H2 receptor, or histamine2, is a subtype of histamine receptor that binds histamine and mediates several physiological responses. It is a G protein-coupled receptor that primarily signals through the Gs protein to activate adenylyl cyclase, increasing intracellular cyclic AMP and triggering downstream effects.

In the stomach, H2 receptors are highly expressed on parietal cells and regulate gastric acid secretion. Histamine released from enterochromaffin-like cells in response to gastrin and vagal stimulation binds these receptors, enhancing proton pump activity and acid production. This mechanism works alongside other stimulants such as gastrin and acetylcholine to control gastric acidity.

Beyond the stomach, H2 receptors are found in various tissues, including the brain, heart, and immune cells, where they participate in modulating neurotransmitter release, vascular tone, and certain immune responses. Their overall physiological roles are diverse but are most prominently linked to gastric acid secretion and mucosal defense.

Pharmacologically, histamine H2 receptors are targetted by H2 receptor antagonists, which block histamine binding and markedly reduce acid secretion. These drugs are used to treat peptic ulcers, gastroesophageal reflux disease (GERD), dyspepsia, and Zollinger-Ellison syndrome. Common H2 antagonists include famotidine, ranitidine, cimetidine, and nizatidine. Cimetidine, in particular, can inhibit certain cytochrome P450 enzymes, leading to drug interactions and, in some cases, antiandrogenic effects. Adverse effects are generally mild but can include headaches, constipation, or confusion in sensitive individuals.

Histamine H2 receptors are one of four histamine receptor subtypes (H1–H4). They play a central role in gastric physiology and contribute to various systemic processes, making them important in clinical pharmacology and disease management.