Free fatty acid eicosanoid precursors

Unsaturated C2o-fatty acids are precursors of the eicosanoids (D 3.2.6). 3-Acetoxy fatty acids (3-acetoxypalmitic, -stearic and -arachidic acid) are formed from the corresponding hydroxylated acids in floral glands of some families of Angio-spermae. They are collected by bees during pollination (E 5.5.1) either in the free state or as glycerides (D 3.2.4) and used to feed the larvae. 

Only the free form of the fatty acid precursors of eicosanoids can be utilized by the enzymes for conversion to the biologically active metabolites. However, the amount of precursor free fatty acid in the cytoplasm and circulating is usually low and so too is basal eicosanoid formation. Eurthermore, basal eicosanoid formation may depend on dietary and adipose tissue fatty acid composition. The amount of eicosanoid precursor free fatty acids is controlled to a large extent by incorporation and release from cellular phospholipids. Which eicosanoids are produced during stimulated synthesis may depend on membrane fatty acid composition as well as the cell type involved. Dietary fatty acid composition, therefore, has the potential to effect basal and stimulated synthesis of eicosanoids and influence endothelial function and thrombotic and inflammatory responses. 

Arachidonic acid, a 20-carbon fatty acid, is the primary precursor of the prostaglandins and related compounds (see Figure 39.3). Arachidonic acid is present as a component of the phospholipids of cell membranes, primarily phosphatidyl inositol and other complex lipids.1 Free arachidonic acid is released from tissue phospholipids by the action of phospholipase A2 and other acyl hydrolases, via a process controlled by hormones and other stimuli (see Figure 39.3). There are two major pathways in the synthesis of the eicosanoids from arachidonic acid (see Figure 39.3). 

The little success of search for prostaglandins in plant tissues is probably not accidental. To evaluate the perspectives of search for eicosanoids or their analogs it is necessary to take into account the relative abundance of different poly-enoic fatty acids in plants. Most plants, according to all available data, are free of metabolic precursors of eicosanoids,... 

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