Histamine

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Contents

Synthesis

Histamine is formed by decarboxylation of the amino acid histidine. The enzyme that catalyzes this step differs from the L-aromatic amino acid decarboxylases that decarboxylate 5-hydroxytryptophan and L-dopa.

Anatomy

Histaminergic neurons have their cell bodies in the tuberomammillary nucleus of the posterior hypothalamus, and their axons project to all parts of the brain, including the cerebral cortex and the spinal cord.

Histamine is also found in cells in the gastric mucosa and in heparin-containing mast cells that are common in the anterior and posterior lobes of the pituitary gland.

Receptors

The four known subtypes of histamine receptors, all of which are G protein coupled metabotropic receptors:

  1. H1
  2. H2
  3. H3 (most sensitive to histamine)
  4. H4

H1 receptors activate phospholipase C, and H2 receptors increase the intracellular cAMP concentration.

Most of the H3 receptors are presynaptic, and they mediate inhibition of the release of histamine and other transmitters via a G protein.

Expression of H4 receptors seems to be restricted to cells of hematopoietic origin: eosinophils, T cells, mast cells, basophils, and dendritic cells.

Function

The function of the histaminergic system in the brain is uncertain, but histamine thought to regulate arousal, body temperature, and vascular dynamics.

References

  1. Goodman LS, Gilman A, Brunton LL, Lazo JS, Parker KL. Goodman & Gilman's the pharmacological basis of therapeutics. 11th / ed. New York: McGraw-Hill; 2006.
  2. Katzung BG. Basic & clinical pharmacology. 10th ed. New York: McGraw-Hill Medical; 2007.
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