Histamine exerts its actions by combining with specific cellular histamine receptors. The four histamine receptors that have been discovered are designated H1 through H4.
|H1 histamine receptor||Found on smooth muscle, endothelium, and central nervous system tissue||Causes vasodilation, bronchoconstriction, bronchial smooth muscle contraction, separation of endothelial cells (responsible for hives), and pain and itching due to insect stings; the primary receptors involved in allergic rhinitis symptoms and motion sickness.|
|H2 histamine receptor||Located on parietal cells||Primarily stimulate gastric acid secretion|
|H3 histamine receptor||Found on central nervous system and to a lesser extent peripheral nervous system tissue||Decreased neurotransmitter release: histamine, acetylcholine, norepinephrine, serotonin|
|H4 histamine receptor||Found primarily in the basophils and in the bone marrow. It is also found on thymus, small intestine, spleen, and colon.||Plays a role in chemotaxis.|
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