• Source: Histamine H2 receptor

H2 receptors are a type of histamine receptor found in many parts of the anatomy of humans and other animals. They are positively coupled to adenylate cyclase via Gs alpha subunit. It is a potent stimulant of cAMP production, which leads to activation of protein kinase A. PKA functions to phosphorylate certain proteins, affecting their activity. The drug betazole is an example of a histamine H2 receptor agonist.


<h2>Functionh2>
Histamine is a ubiquitous messenger molecule released from mast cells, enterochromaffin-like cells, and neurons. Its various actions are mediated by histamine receptors H1, H2, H3 and H4. The histamine receptor H2 belongs to the rhodopsin-like family of G protein-coupled receptors. It is an integral membrane protein and stimulates gastric acid secretion. It also regulates gastrointestinal motility and intestinal secretion and is thought to be involved in regulating cell growth and differentiation. Histamine may play a role in penile erection.


<h2>Tissue distributionh2>
Histamine H2 receptors are expressed in the following tissues:

Peripheral tissues
Gastric parietal cells (oxyntic cells)
Vascular smooth muscle
Neutrophils
Mast cells
Heart
Genitourinary system (uterus, bladder)

Central nervous system tissues
Caudate–putamen
Cerebral cortex (external layers)
Hippocampal formation
Dentate nucleus of the cerebellum


<h2>Physiological responsesh2>
Activation of the H2 receptor results in the following physiological responses:

Stimulation of gastric acid secretion (Target of anti-histaminergics (H2 receptors) for peptic ulcer disease and GERD)
Smooth muscle relaxation (Experimental histamine H2 receptor agonist used for asthma and COPD)
Inhibit antibody synthesis, T-cell proliferation and cytokine production
Vasodilation – PKA activity causes phosphorylation of MLCK, decreasing its activity, resulting in MLC of myosin being dephosphorylated by MLCP and thus inhibiting contraction. The smooth muscle relaxation leads to vasodilation.
Inhibition of neutrophil activation and chemotaxis


<h2>See alsoh2>
H2-receptor antagonist
Histamine H1-receptor
Histamine H3-receptor
Histamine H4-receptor


<h2>Referencesh2>


<h2>Further readingh2>


<h2>External linksh2>
"Histamine Receptors: H2". IUPHAR Database of Receptors and Ion Channels. International Union of Basic and Clinical Pharmacology.
H2+receptors at the U.S. National Library of Medicine Medical Subject Headings (MeSH)
This article incorporates text from the United States National Library of Medicine, which is in the public domain.

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