Prostaglandins (PGs) and leukotrienes (LTs) belong to a large, heterogeneous group of lipid mediators, collectively named eicosanoids, that exhibit a diverse array of physiological activities (Figure 1). Eicosanoids are synthesized by oxygenation and remodeling of their precursor 20-carbon polyunsaturated fatty acids (PUFAs), namely arachidonic acid (AA; 20:4 n-6). Whilst pivotally involved in many homeostatic processes, eicosanoids are also implicated in the patho-physiology of many chronic disorders (Figure 1). Since the discovery in the mid 1930s of prostaglan-dins as a component of human semen that potently induced uterine contractility, the field of eicosanoid biology has expanded to include the PGs, LTs, thromboxanes (TXs), hydroxyeicosatetraenoic acids (HETEs), lipoxins (LXs, including epi-lipoxins), isoprostanes, and the cyclopentaeone PGs
(Figure 2). Except the latter two classes, which are generated by nonenzymatic oxidation, synthesis of these mediators is tightly regulated by a number of enzymes. Eicosanoids generally act as paracrine or autocrine agents, in that they exert their biological effects locally, either on the cell from which they were synthesized or on neighboring cells. This chapter will focus primarily on the synthesis and physiological roles of the PGs and LTs and the regulation of their synthesis by dietary fatty acids.
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