Thromboxanes and and prostaglandins are eicosanoids that are derived from a common pathway (Figure 19.30), whereas the related leukotrienes are derived from arachidonic acid via a different pathway.
Structures of the major prostaglandins and thromboxane A2 are shown in Figure 19.29. Thromboxane A2 and, to a lesser extent, prostaglandins, induce platelet aggregation, an early step in blood clot formation.
Eicosanoids (like prostaglandin) exert specific physiological effects on target cells, like hormones. However, eicosanoids are distinct from most hormones in that they cat locally, near their sites of synthesis, and they are catabolized extremely rapidly. Thus, eicosanoids are considered to be locally acting hormones.
1. Eicosanoids