Eicosanoids are a class of lipids that include the prostaglandins, thromboxanes, and leukotrienes. Eicosanoids derive their name from their common origin, that is, from C20 polyunsaturated fatty acids, the eicosaenoic acids, particularly arachidonic acid (all-cis-5,8,11,14-eicosatetraenoic acid). Related trienoic and pentaenoic acids are minor precursors to some of these compounds.

Prostaglandins and thromboxanes are derived from a common pathway (See Figure 19.30), whereas leukotrienes are derived from arachidonic acid via a different pathway.

Structures of the major prostaglandins and thromboxane A2 are shown in Figure 19.29. In the names of prostaglandins, such as PGF2, PGE2, or PGF2, the subscripted number refers to the number of double bonds in the molecule and the / designation indicates whether the hydroxyl group at position 9 is cis to the 11-hydroxyl () or trans to the 11-hydroxyl ().

Eicosanoids exert specific physiological effects on target cells, like hormones. However, eicosanoids are distinct from most hormones in that they act locally, near their sites of synthesis, and they are catabolized extremely rapidly. Thus, eicosanoids are considered to be locally acting hormones.

1. Eicosanoids

2. Prostaglandin and Leukotriene Metabolism