Release stimulation
Histamine is usually released by degranulation of the storing cell. This is triggered by a rise in intracellular calcium. Mechanisms which produce this rise include:
- complement components C3a and C5a binding to receptors on the cell surface
- binding of IgE to cell surface in association with antigen
- histamine-releasing factors from various leukocytes e.g. neutrophils
- platelet activation e.g. contact with collagen, antigen-antibody complexes
- physical agents e.g. cold or trauma
- the cytokine interleukin-1
Release is less likely if cyclic AMP concentration is elevated. Beta-adrenoceptor agonists may modulate histamine-producing cells in this way.
Once released, the effects of histamine are reduced by:
- diffusion away from the site
- histaminase enzymes
- acetylation
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