Histamine

Describe the physiology of histamine and serotonin

Histamine is an endogenous amine produced by decarboxylation of histidine. Histamine is:

  • Present in all tissues
    Particularly abundant in those exposed to the outside environment:
    • Lungs
    • Gut
    • Skin (lungs, gut, skin)
  • Produced in and released by:
    • Mast cells
      Released by exocytosis during inflammatory and allergic reactions.
    • Basophils
    • Histaminocytes in the stomach
    • Histaminergic neurons in the CNS
  • Metabolised by:
    • Histaminase
    • Imidazole N-methyltransferase

Histamine Receptors and Effects

Histamine acts on:

  • H1 receptors
    Gq receptor involved broadly in inflammation and vasodilation.
  • H2 receptors Gs receptor involved in gastric acid secretion.
  • H3 receptors
    Gi presynaptic receptor in the CNS.
  • H4 receptors
    Gi receptor located in bone marrow and other solid haematological organs (spleen, liver, thymus).
System H1 H2 H3 H4
Resp Bronchoconstriction Bronchodilation
CVS ↑ Vasodilation (endothelial effect), coronary vasoconstriction, ↓ AV nodal conduction ↑ HR, ↑ inotropy, coronary vasodilation, ↑ capillary permeability
CNS Presynaptic inhibition of neurotransmission
MSK Weal due to local vasodilation, itch, ↑ nociception
GIT ↑ Peristalsis ↑ Gastric acid secretion
Haeme Alter IL-16 release

References

  1. Parsons ME, Ganellin CR. Histamine and its receptors. British Journal of Pharmacology. 2006;147(Suppl 1):S127-S135. doi:10.1038/sj.bjp.0706440.
  2. Rang HP, Dale MM, Ritter JM, Flower RJ. Rang and Dale's Pharmacology. 6th Ed. Churchill Livingstone.
  3. Bowen R. Histamine. Vivo. Colorado State.
Last updated 2017-09-17

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