Prostanoids are the cyclooxygenase metabolites derived from C-20 unsaturated fatty acids and include prostaglandin (PG) D2, PGE2, PGF2 alpha, PGI2, and thrombaxane (Tx) A2. Prostaglandin A, B, and C are believed not to occur naturally. Arachidonic acid is the most abundant fatty acid precursor for the production of various PG. The fatty acids precursors are released from the membrane phosphoplipids in response to various physiological and pathological stimuli by the action of phospholipase A2 and are converted to various prostanoids by the sequential actions of cyclooxygenases and the respective synthases. Prostanoids are released outside the cells and exert a variety of actions.

Prostaglandin PGE2 is one of the major prostaglandin produced during inflammation. A variety of PGE2-mediated effects on vascular smooth muscle tonus, glomerular cell function, renin release, and renal salt and water transport have been described. PGs also influence neuronal activity by modulating neurotransmitter release, sensitizing secretory fibers to noxious stimuli, or inducing fever and sleep. The actions of PGE2 are mediated by rhodopsin-type; G-protein coupled membrane receptors, termed E-prostanoid (EP) receptors or PTGERs. There are four subtypes of PGE receptors designated as EP1, EP2, EP3, and EP4 that are encoded by different genes and expressed differently in each tissue. The intracellular signaling also differs among the receptor subtypes. Stimulation of the EP1 receptors results in activation of phosphatidylinositol (PI) hydrolysis and in elevation of intracellular Ca++ concentration. EP2 and EP4 increase intracellular camp through activation of adenyl cyclase. The EP3 inhibits adenylate cyclase leading to a decrease of camp. In general, EP receptors display a protein topology typical of GPCR - 7 TM domain, an extracellular N-terminus, and a large intracellular C-terminus.

EP1 (mouse/rat 405 aa, human 402 aa, chromosome 19p13.1; ~ 84% interspecies homology) expression is restricted to kidney (papillary collecting ducts), lung, and

stomach (muscularis mucosae layer), spleen, skeletal muscle, testis, and uterus. EP1 has also been localized in neurons of the DRG. An alternatively spliced variant, a 366-aa protein carrying a specific change if 49 aa from the middle of TM VI to C-terminus, has also been described in rat uterus. The variant is also expressed in the kidney.

EP2 or PTGER2 (rat 357 aa, mouse 362 aa, and human 358 aa; chromosome 14; ~85% interspecies homology) has wide tissue distribution, with high expression in lung and placenta. Ep2 -/- females are infertile secondary to failure of the released ovum to become fertilized in vivo. Besides its effects on reproduction, PGE2 regulates regional blood flow in various vascular beds. Mice deficient in the EP2 receptor displayed resting systolic blood pressure that was significantly lower than that in wild type controls. LPS induces EP2 in macrophages.

EP3 (mouse 3-4 isoforms, 365-425 aa; rat 2 isoforms 364-365 aa; human 3-6 isoforms, 365-425 aa, chromosome 1p31.2,) is expressed in the kidney, brain, stomach, uterus, liver, skeletal muscle, intestine, and thymus. Alternative splicing of EP3 produces various isoforms (alpha, beta, gamma, etc) with different C-terminal tails. EP3 isoforms have identical ligand binding but different coupling properties with G-proteins: alpha and beta coupled to Gi, whereas gamma couples with Gi and Gs. EP3 knockout mice show impaired febrile response to pyrogens.

EP4 (mouse 513 aa, rat 488 aa; human 488 aa, chromosome 5p13.1, ~ 90% interspecies homology) is expressed in intestine, lung, thymus, kidney, uterus, pancreas, spleen, heart, stomach, and brain. EP4 knockout mice show patent ductus arteriosus, and decreased inflammatory bone resorption. EP4 activity is mediated by Gs that stimulate adenyl cyclase. It has a relaxing effect on smooth muscle and implicated in renal hemodynamics, intestinal epithelial transport, adrenal aldosterone secretion, and uterine functions. It was originally reported as EP2 subtype.

m=mouse; r=rat; h=human; b=bovine; d=dog; ~CT or ~NT=near C or N-terminus. EC=Extracellular; CP=Cytoplasmic domain;

"Neat Antisera" are the unpurified antiserum and it is suitable for ELISA and Western.
"Affinity pure" IgG may be more suitable for immunohistochemical applications and to reduce background in most applications.
"Control peptides" cannot be used for Western as they are very short peptides. They are intended for ELISA or antibody blocking studies to establish antibody specificity.