Definition : The chemical mediators are the substances that initiate & regulate inflamma tory reactions.
**The most important mediators of acute inflam mation are vasoactive amines, lipid products (prostaglandins and leukotrienes), cytokines (including chemokines), and products of complement activation.
**I Cell-derived mediators are normally seques tered in intracellular granules & can be rapidly secreted by granule exocytosis (eg., histamine in mast cell granules) or are synthesized de novo (eg., prostaglandins and leukotrienes, cytokines) in response.
**Mediators are either secreted by cells or generated from plasma proteins.
#**Macrophages, dendritic cells, and mast cells produce chemical mediators but platelets, neutrophils, endothelial cells, and most epithelia can also be induced to elaborate some of the mediators.
** Active mediators are produced only in response to various stimuli.
** Most of the mediators are short-lived.
**One mediator can stimulate the release of other mediators.
Arachidonic Acid Metabolites Arachidonic acid (AA) is a 20 carbon poly unsaturated fatty acid.
Formed from cell membrane phospholipids by enzyme
**phospholipase. Phospholipase activated by physical and chemical stimuli or by mediators. Steroid inhibit Phospholipase. Arachidonic acid metabolites are Prostaglandins (PGI2 PGE, PGE, PGF), Prostacyclin (PGI), Thromboxane A2 ,Leukotrienes (C4, D4, E) and lipoxins (A4, Ba).
