Most of the eicosanoid receptors are integral membrane protein G protein-coupled receptors (GPCRs) that bind and respond to eicosanoid signaling molecules. Eicosanoids are rapidly metabolized to inactive products and therefore are short-lived. Accordingly, the eicosanoid-receptor interaction is typically limited to a local interaction: cells, upon stimulation, metabolize arachidonic acid to an eicosanoid which then binds cognate receptors on either its parent cell (acting as an Autocrine signalling molecule) or on nearby cells (acting as a Paracrine signalling molecule) to trigger functional responses within a restricted tissue area, e.g. an inflammatory response to an invading pathogen. In some cases, however, the synthesized eicosanoid travels through the blood (acting as a hormone-like messenger) to trigger systemic or coordinated tissue responses, e.g. prostaglandin (PG) E2 released locally travels to the hypothalamus to trigger a febrile reaction (see ). An example of a non-GPCR receptor that binds many eicosanoids is the PPAR-γ nuclear receptor. The following is a list of human eicosanoid GPCRs grouped according to the type of eicosanoid ligand that each binds: Leukotriene Leukotrienes: BLT1 (Leukotriene B4 receptor) – ; BLT1 is the primary receptor for leukotriene B4. Relative potencies in binding to and stimulating BLT1 are: leukotriene B4>20-hydroxy-leukotriene B4>>12-Hydroxyeicosatetraenoic acid (R isomer) (http://www.guidetopharmacology.org/GRAC/ObjectDisplayForward?objectId=267; also see ALOX12B and 12-Hydroxyeicosatetraenoic acid). BLT1 activation is associated with pro-inflammatory responses in cells, tissues, and animal models. BLT2 (Leukotriene B4 receptor 2) – ; the receptor for 12-Hydroxyheptadecatrienoic acid, leukotriene B4, and certain other eicosanoids and polyunsaturated fatty acid metabolites (see BLT2). Relative potencies in binding to and stimulating BLT2 are: 12-hydroxyheptadecatrienoic acid (S isomer)>leukotriene B4>12-Hydroxyeicosatetraenoic acid (S isomer)= 12-hydroperoxyeicosatetraenoic acid (S isomer)>15-Hydroxyeicosatetraenoic acid (S isomer])>12-hydroxyeicosatetraenoic acid (R isomer)>20-hydroxy-leukotriene LTB4 (http://www.guidetopharmacology.org/GRAC/ObjectDisplayForward?objectId=268). Activation of BLT2 is associated with pro-inflammatory responses by cells and tissues. CysLT1 (Cysteinyl leukotriene receptor 1) – ;CYSLTR1 is the receptor for Leukotriene C4 and Leukotriene D4; in binds and responds to leukotriene C4 more strongly than to leukotriene D4. Relative potencies for binding to and activation CYSLTR1 are: leukotriene C4≥ leukotriene D4>>leukotriene E4 (http://www.guidetopharmacology.org/GRAC/ObjectDisplayForward?objectId=270). Activation of this receptor is associated with pro-allergic responses in cells, tissues, and animal models. CysLT2 (Cysteinyl leukotriene receptor 2) – ; Similar to CYSLTR1, CYSLTR2 is the receptor for Leukotriene C4 and Leukotriene D4; it binds and responds to the latter two ligands equally well. Relative potencies in binding to and stimulating CYSLTR2 are: leukotriene C4≥leukotriene D4>>leukotriene E4 (http://www.guidetopharmacology.org/GRAC/ObjectDisplayForward?objectId=270). CYSLT2 Activation of this receptor is associated with pro-allergic