the 5-oxo-ETE/OXER1 axis may play an important role in feline asthma, a common condition in this species, and that felines could serve as a useful animal model to investigate the pathophysiological role of 5-oxo-ETE in asthma and other conditions. Ligands The OXER1 G protein-coupled receptor resembles the hydroxy carboxilic acid subfamily of G protein-coupled receptors, which besides GPR109A, niacin receptor 1, and niacin receptor 2 may include the recently defined receptor for 12-HETE, GPR31, not only in its amino acid sequence but also in the hydroxy-carboxylic acid nature of its cognate ligands. Naturally occurring ligands for OXER1 are long chain polyunsaturated fatty acids containing either a hydroxyl (i.e. -OH) or oxo (i.e. =O, keto) residue removed by 5 carbons from each of these acid's carboxy residue. Agonists OXER1 is known or presumed to bind and thereby be activated by the following endogenous arachidonic acid metabolites; 5-oxo-ETE>5-oxo-15-hydroxy-ETE>5-hydroperoxyicosatetraenoic acid (5-HpETE)>5-HETE>5,20-diHETE. OXER1 is also activated by metabolites of other polyunsaturated fatty acids that therefore may be categorized as members of the 5-oxo-ETE family of agonists; these agonists include 5(S)-oxo-6E,8Z,11Z-eicosatrienoic acid (a 5-LO metabolite of mead acid); 5(S)-hydroxy-6E,8Z-octadecadienoic acid and 5(S)-oxo-6E,8Z-octadecadienoic acid (5-LO metabolites of sebaleic acid, i.e. 5Z,8Z-octadecadienoic acid); and 5(S)-hydroxy-6E,8Z,11Z,14Z,17Z-eicosapentaenoic and 5-oxo-6E,8Z,11Z,14Z,17Z-eicosapentaenoic acids (5-LO metabolites of the n-3 polyunsaturated fatty acid, eicosapentaenoic acid). Antagonists 5-Oxo-12(S)-hydroxy-HETE and its 8-trans isomer, 5-oxo-12(S)-hydroxy-6E,8E,11Z,14Z-eicosatetraenoic acid, and a series of synthetic mimetics of 5-oxo-ETE structure (compounds 346, S-264, S-230, Gue154, and still to be named but considerably more potent drugs than these) block the activity of 5-oxo-ETE but not other stimuli in leukocytes and are presumed to be OXER1 antagonists. Mechanisms of activating cells OXE-R couples to the G protein complex Gαi-Gβγ; when bound to a 5-oxo-ETE family member, OXE-R triggers this G protein complex to dissociate into its Gαi and Gβγ components. Gβγ appears to be the component most responsible for activating many of the signal pathways that lead to cellular functional responses. Intracellular cell-activation pathways stimulated by OXER1 include those involving rises in cytosolic calcium ion levels, and along with others that lead to the activation of MAPK/ERK, p38 mitogen-activated protein kinases, cytosolic Phospholipase A2, PI3K/Akt, and protein kinase C beta (i.e. PRKCB1, delta (i.e. PRKCD), epsilon (i.e. PRKCE), and zeta (i.e. PRKCZ). Function OXER1 is activated by 5-oxo-ETE, 5-HETE, and other members of the 5-Hydroxyicosatetraenoic acid family of arachidonic acid metabolites and thereby mediates this family's stimulatory effects on cell types that are involved