PCOL2605 Lecture Notes - Lecture 10: Tumor Necrosis Factor Superfamily, Histidine Decarboxylase, Histamine H1 Receptor
10 Oct 2018
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Document Summary
Histamine is a formed by the decarboxylation of the amino acid histidine by the enzyme histidine decarboxylase. Small amounts of histamine is found free in most tissues, but the vast majority is stored in the tissues in mast cells, and in the blood in basophils (circadian gene clock in mast cells regulates histamine transport) As well as histamine, mast cells contain heparin and tumour necrosis factor and they can synthesise leukotrienes and prostaglandins. The lungs, gastrointestinal tract and skin have the highest number of mast cells (immune function) Histamine exerts its effects by acting as an agonist on four different types of histamine receptors. These are named h1, h2, h3 and h4, and all are g-protein coupled receptors. Stimulation of h1 receptors (gq) by histamine produces: Smooth muscle contraction e. g. gastrointestinal and bronchiole (which can result in bronchoconstriction) An increase in the permeability of post-capillary venules. Stimulation of h2 receptors (gs) by histamine produces.
