What is Platelate Activated factor?? PAF content of human sperm has a positive correlation with fertilizing potential and pregnancy outcome.

Ans :- PAF content of human sperm has a positive correlation with fertilizing potential and pregnancy outcome. Produced by variety of cell types. Several studies suggest that PAF appears to mediate sperm motility by inducing the formation of inositol triphosphate and diacylglycerol and by increasing intracellular calcium. PAF content of human sperm has a positive correlation with fertilizing potential and pregnancy outcome.  Platelet-activating factor, also known as PAF, PAF-acether or AGEPC (acetyl-glyceryl-ether-phosphorylcholine), is a potent phospholipid activator and mediator of many leukocyte functions, 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.. Cllinical

High PAF levels are associated with a variety of medical conditions. Some of these conditions include:

•Allergic reactions
•Stroke
•Sepsis
•Myocardial infarction
•Colitis, inflammation of the large intestine
•Multiple sclerosis

While the effects that PAF has on inflammatory response and cardiovascular conditions are well understood, PAF is still a hot subject for discussion. Over the past 15 years, papers written on PAF have almost doubled from approximately 7,500 in 1997 to 13,000 in 2012.^{[citation needed]} Research into PAF is ongoing.

Anti-PAF drugs

Anti-PAF drugs are currently being used in cardiac rehabilitation trials. Anti-PAF drugs are used to block angiotensin II type 1 receptors to lower in the risk of atrial fibrillation in individuals with paroxysmal fibrillation. It is also used to lessen the effects of allergies.

PAF is produced by a variety of cells, but especially those involved in host defense, such as platelets, endothelial cells, neutrophils, monocytes, and macrophages. PAF is continuously produced by these cells but in low quantities and production is controlled by the activity of PAF acetylhydrolases. It is produced in larger quantities by inflammatory cells in response to specific stimuli.^[1] AF is produced by stimulated basophils, monocytes, polymorphonuclear neutrophils, platelets, and endothelial cells primarily through lipid remodeling. A variety of stimuli can initiate the synthesis of PAF. These stimuli could be macrophages going through phagocytosis or endothelium cells uptake of thrombin.

There are two different pathways in which PAF can be synthesized: de novo pathway and remodeling. The remodeling pathway is activated by inflammatory agents and it is thought to be the primary source of PAF under pathological conditions. The de novo pathway is used to maintain PAF levels during normal cellular function.

The most common pathway taken to produce PAF is remodeling. The precursor to the remodeling pathway is a phospholipid, which is typically phosphatidylcholine (PC). The fatty acid is removed from the sn-2 position of the three-carbon backbone of the phospholipid by phospholipase A2 (PLA2) to produce the intermediate lyso-PC (LPC). An acetyl group is then added by LPC acetyltransferase (LPCAT) to produce PAF.

Using the de novo pathway, PAF is produced from 1-O-alkyl-2-acetyl-sn-glycerol (AAG). Fatty acids are joined on the sn-1 position with 1-O-hexadecyl being the best for PAF activity. Phosphocholine is then added to the sn-3 site on AAG creating PAF.

The concentration of PAF is controlled by the synthesis of the compound and by the actions of PAF acetylhydrolases (PAF-AH). PAF-AH are a family of enzymes that have the ability to catabolize and degrade PAF and turn it into an inactive compound. The enzymes within this family are lipoprotein-associated phospholipase A2, cytoplasmic platelet-activating factor acetylhydrolase 2, and platelet-activating factor acetylhydrolase 1b.

Cations are one form of regulation in the production of PAF. Calcium plays a large role in the inhibition of enzymes that produce PAF in the denovo pathway of PAF biosynthesis.

The regulation of PAF is still not completely understood. Enzymes that are associated with the production of PAF are controlled by metal ions, thiol compounds, fatty acids, pH, compartmentalization, and phosphorylation and dephosphorylation. These controls on these PAF producing enzymes are believed to work in conjunction to control it, but the overall pathway and reasoning is not well understood.