Histamine Receptor - Comparison

Comparison

Histamine receptors
Receptor	Mechanism	Function	Antagonists
H₁	G_q	ileum contraction modulate circadian cycle itching systemic vasodilatation bronchoconstriction (allergy-induced asthma)	H₁-receptor antagonists Diphenhydramine Loratadine Cetirizine Fexofenadine
H₂	G_s ↑ Ca2+	speed up sinus rhythm Stimulation of gastric acid secretion Smooth muscle relaxation Inhibit antibody synthesis, T-cell proliferation and cytokine production	H₂-receptor antagonists Ranitidine Cimetidine Famotidine Nizatidine
H₃	G_i	Decrease Acetylcholine, Serotonin and Norepinephrine Neurotransmitter release in CNS Presynaptic autoreceptors	H₃-receptor antagonists ABT-239 Ciproxifan Clobenpropit Thioperamide
H₄	G_i	mediate mast cell chemotaxis.	H₄-receptor antagonists Thioperamide JNJ 7777120

There are several splice variants of H₃ present in various species. Though all of the receptors are 7-transmembrane g protein coupled receptors, H₁ and H₂ are quite different from H₃ and H₄ in their activities. H₁ causes an increase in PIP₂ hydrolysis, H2 stimulates gastric acid secretion, and H3 mediates feedback inhibition of histamine.

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