Histamine Receptors

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Chapter: Essential pharmacology : Histamine And Antihistaminics

Analogous to adrenergic αand β receptors, histaminergic receptors were classified by Asch and Schild (1966) into H1 and H2 : those blocked by then available antihistamines were labelled H1. Sir James Black (1972) developed the first H2 blocker burimamide and confirmed this classification.


HISTAMINE RECEPTORS     

 

Analogous to adrenergic αand β receptors, histaminergic receptors were classified by Asch and Schild (1966) into H1 and H2 : those blocked by then available antihistamines were labelled H1. Sir James Black (1972) developed the first H2 blocker burimamide and confirmed this classification. Both H1 and H2 receptors have now been cloned. A third H3 receptor, which serves primarily as an autoreceptor controlling histamine release from neurones in brain was identified in 1983. Though some selective H3 agonists and antagonists have been produced, none has found any clinical application. Features of these 3 type of histaminergic receptor are compared in Table 11.1.

 


 

Molecular cloning has revealed yet another (H4) receptor in 2001. It has considerable homology with H3 and binds many H3 ligands. Eosinophils, mast cells and basophils are the primary cells expressing H4 receptors; activation enhances chemotaxis of these cells. The H4 receptor may be playing a role in allergic inflammation: H4 antagonists are being explored as potential drugs for allergic inflammatory conditions like rhinitis and asthma. Intestines and brain are the other sites where H4 receptors have been located.

 

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