Platelet-activating factor

Platelet-activating factor
Platelet-activating factor
CAS number 74389-68-7 YesY
PubChem 108156
ChemSpider 26286744 YesY
MeSH Platelet+Activating+Factor
IUPHAR ligand 1831
Jmol-3D images Image 1
Molecular formula C26H54NO7P
Molar mass 523.68 g mol−1
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Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Platelet-activating factor, also known as a PAF, PAF-acether or AGEPC (acetyl-glyceryl-ether-phosphorylcholine) is a potent phospholipid activator and mediator of many leukocyte functions, including platelet aggregation and degranulation, inflammation, and anaphylaxis. It is also involved in changes to vascular permeability, the oxidative burst, chemotaxis of leukocytes, as well as augmentation of arachidonic acid metabolism in phagocytes.

It is produced in response to specific stimuli by a variety of cell types, including neutrophils, basophils, injured tissue, monocytes/macrophages, platelets, and endothelial cells.



Several molecular species of platelet-activating factor that vary in the length of the O-alkyl side-chain have been identified.

  • Its alkyl group is connected by an ether linkage at the C1 carbon to a 16-carbon chain.
  • The acyl group at the C2 carbon is an acetate unit (as opposed to a fatty acid) whose short length increases the solubility of PAF, allowing it to function as a soluble signal messenger.
  • The C3 has a phosphocholine head group, just like standard phosphatidylcholine.


It is an important mediator of bronchoconstriction.

It causes platelets to aggregate and blood vessels to dilate. Thus, it is important to the process of hemostasis. At a concentration of 10-12 mol/L, PAF causes life threatening inflammation of the airways to induce asthma like symptoms.

Toxins such as fragments of destroyed bacteria induce the synthesis of PAF, which causes a drop in blood pressure and reduced volume of blood pumped by the heart, which leads to shock and possibly death.


It was discovered by French immunologist Jacques Benveniste in the early 1970s.[1][2] Its structure was elucidated by Constantinos A. Demopoulos in 1979.[3]

Biosynthesis and degradation

PAF is biosynthesized from lysophosphatidylcholine (LPC) and acetyl CoA by the enzyme LPC acetyltransferase (LPCAT). It is also derived from 2-acetyl monoalkylglycerol ether by phosphocholine transferase.

It is degraded (thereby terminating its capacity to act as a signaling molecule) by a group of enzymes called PAF acetylhydrolases (PAFAHs), which are related to phospholipase A2.


  • SM-12502 is a PAF antagonist, which is metabolized in the liver by the enzyme CYP2A6.[4]
  • Rupatadine is an antihistamine and PAF antagonist used to treat allergies.

See also


  1. ^ Benveniste J, Henson PM, Cochrane CG (1972). "Leukocyte-dependent histamine release from rabbit platelets. The role of IgE, basophils, and a platelet-activating factor". J. Exp. Med. 136 (6): 1356–77. doi:10.1084/jem.136.6.1356. PMC 2139324. PMID 4118412. 
  2. ^ Benveniste J (1974). "Platelet-activating factor, a new mediator of anaphylaxis and immune complex deposition from rabbit and human basophils". Nature 249 (457): 581–2. doi:10.1038/249581a0. PMID 4275800. 
  3. ^ Demopoulos CA, Pinckard RN, Hanahan DJ (1979). "Platelet-activating factor. Evidence for 1-O-alkyl-2-acetyl-sn-glyceryl-3-phosphorylcholine as the active component (a new class of lipid chemical mediators)" (abstract). J. Biol. Chem. 254 (19): 9355–8. PMID 489536. 
  4. ^ Platelet-Activating Factor Antagonist, SM-12502, Attenuates ...

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