Leukotriene and related receptors are activated by the endogenous ligands leukotriene (LT) B4, LTC4, LTD4, LTE4 and 12-HETE. Leukotrienes are lipid mediators synthesized from arachidonic acid by lipoxygenase enzymes. They act on peroxisome-proliferating receptors (PPARs) as well as the G-protein-coupled leukotriene receptors, and are important in inflammatory signaling pathways. Leukotriene and related receptors are high affinity stereoselective receptors that have a wide biological distribution. BLT1 and BLT2 receptors are synthesized by polymorphonuclear leukocytes and are found at their highest concentrations on myeloid cells, mast cells and macrophages.