Characterization of murine vasopressor and vasodepressor prostaglandin E(2) receptors

Stimulation of prostanoid IP and EP2 receptors dilates retinal arterioles and increases retinal and choroidal blood flow in rats

We examined the effects of vasodilatory prostaglandins (prostacyclin and prostaglandin E(2)) and selective agonists for prostanoid EP(2) and EP(4) receptor on the diameters of retinal blood vessels and fundus (retinal/choroidal) blood flow in rats. Male Wistar rats (8- to 10-week-old) were treated with tetrodotoxin (50 microg/kg, i.v.) to eliminate any nerve activity and prevent movement of the eye and infused with a mixture solution of norepinephrine and epinephrine (1:9) to maintain adequate systemic circulation under artificial ventilation. Fundus images were captured with a digital camera that was equipped with the special objective lens for small animals, and the diameters of retinal arterioles and venules were measured on a personal computer. Fundus blood flow was estimated using a laser Doppler flowmetry. Intravenous infusions of prostacyclin and prostaglandin E(2) dilated retinal blood vessels, increased fundus blood flow and decreased systemic blood pressure in a dose-dependent manner. The effects of vasodilatory prostaglandins on retinal arterioles were greater than those on retinal venules. Similarly, a prostanoid EP(2) receptor agonist (ONO-AE1-259-01) dilated retinal blood vessels, and increased fundus blood flow and decreased systemic blood pressure. However, a prostanoid EP(4) receptor agonist (ONO-AE1-329) failed to increase fundus blood flow, despite its comparable depressor response with those to vasodilatory prostaglandins and the prostanoid EP(2) receptor agonist. The responses to forskolin, an activator of adenylyl cyclase, were very similar to those to prostacyclin and the prostanoid EP(2) receptor agonist. These results suggest that prostacyclin and prostaglandin E(2) act as vasodilators in retinal and choroidal circulation, and prostanoid IP and EP(2) receptors play an important role in the regulation of ocular hemodynamics in rats.

Expression and activity of cyclooxygenase isoforms in skeletal muscles and myocardium of humans and rodents

Conflicting data have been reported on cyclooxygenase (COX)-1 and COX-2 expression and activity in striated muscles, including skeletal muscles and myocardium, in particular it is still unclear whether muscle cells are able to produce prostaglandins (PGs). We characterized the expression and enzymatic activity of COX-1 and COX-2 in the skeletal muscles and in the myocardium of mice, rats and humans. By RT-PCR, COX-1 and COX-2 mRNAs were observed in homogenates of mouse and rat hearts, and in different types of skeletal muscles from all different species. By Western blotting, COX-1 and -2 proteins were detected in skeletal muscles and hearts from rodents, as well as in skeletal muscles from humans. Immunoperoxidase stains showed that COX-1 and -2 were diffusely expressed in the myocytes of different muscles and in the myocardiocytes from all different species. In the presence of arachidonic acid, which is the COX enzymatic substrate, isolated skeletal muscle and heart samples from rodents released predominantly PGE(2). The biosynthesis of PGE(2) was reduced between 50 and 80% (P < 0.05 vs. vehicle) in the presence of either COX-1- or COX-2-selective blockers, demonstrating that both isoforms are enzymatically active. Exogenous PGE(2) added to isolated skeletal muscle preparations from rodents did not affect contraction, whereas it significantly fastened relaxation of a slow type muscle, such as soleus. In conclusion, COX-1 and COX-2 are expressed and enzymatically active in myocytes of skeletal muscles and hearts of rodents and humans. PGE(2) appears to be the main product of COX activity in striated muscles.

Investigation of the pronounced synergism between prostaglandin E2 and other constrictor agents on rat femoral artery

This study investigates the pronounced synergism between the weak contractile action of prostaglandin E(2) (PGE(2)) and strong actions of phenylephrine, U-46619 and K(+) on rat isolated femoral artery. The potency ranking for synergism was SC-46275 (prostanoid receptor agonist selectivity: EP(3)>>EP(1))=sulprostone (EP(3)>EP(1))>17-phenyl PGE(2) (EP(1)>EP(3)). The novel EP(3) antagonist L-798106 (0.2-1microM) blocked the enhanced action of sulprostone (pA(2)=7.35-8.10), while the EP(1) antagonist SC-51322 (1microM) did not (pA(2)<6.0). Matching responses to priming agent and priming agent/sulprostone were similarly suppressed by nifedipine (300nM) and the selective Rho-kinase inhibitors H-1152 (0.1-1microM) and Y-27632 (1-10microM). Our findings implicate an EP(3) receptor in the prostanoid component of contractile synergism. While the synergism predominantly operates through a Ca(2+) influx-Rho-kinase pathway, the EP(3) receptor does not necessarily transduce via Rho-kinase.

Atorvastatin reduces the expression of prostaglandin E2 receptors in human carotid atherosclerotic plaques and monocytic cells: potential implications for plaque stabilization

Prostaglandin E2 (PGE2), the product of cyclooxygenase-2 (COX-2) and prostaglandin E synthase-1 (mPGES-1), acts through its receptors (EPs) and induces matrix metalloproteinase (MMP) expression, which may favor the instability of atherosclerotic plaques. The effect of statins on EPs expression has not been previously studied. The aim of this study was to investigate the effect of atorvastatin (ATV, 80 mg/d, for one month) on EP expression in plaques and peripheral blood mononuclear cells (PBMC) of patients with carotid atherosclerosis. In addition, we studied the mechanisms by which statins could modulate EPs expression on cultured monocytic cells (THP-1) stimulated with proinflammatory cytokines (IL-1beta and TNF-alpha). Patients treated with atorvastatin showed reduced EP-1 (14 +/- 1.8% versus 26 +/- 2%; P < 0.01), EP-3 (10 +/- 1.5% versus 26 +/- 1.5%; P < 0.05), and EP-4 expression (10 +/- 4.1% versus 26.6 +/- 4.9%; P < 0.05) in atherosclerotic plaques (immunohistochemistry), and EP-3 and EP-4 mRNA expression in PBMC (real time PCR) in relation to non-treated patients. In cultured monocytic cells, atorvastatin (10 micromol/L) reduced EP-1/-3/-4 expression, along with COX-2, mPGES-1, MMP-9, and PGE2 levels elicited by IL-1beta and TNF-alpha. Similar results were noted with aspirin (100 micromol/L), dexamethasone (1 micromol/L), and the Rho kinase inhibitors Y-27632 and fasudil (10 micromol/L both). The effect of atorvastatin was reversed by mevalonate, farnesyl pyrophosphate, and geranylgeranyl pyrophosphate. On the whole, we have shown that atorvastatin reduces EPs expression in atherosclerotic plaques and blood mononuclear cells of patients with carotid stenosis and in cultured monocytic cells. The inhibition of EP receptors could explain, at least in part, some of the mechanisms by which statins could modulate the COX-2/mPGES-1 proinflammatory pathway and favor plaque stabilization in humans.

The endocannabinoid arachidonyl ethanolamide (anandamide) increases pulmonary arterial pressure via cyclooxygenase-2 products in isolated rabbit lungs

Several cannabinoids elicit systemic vasodilation, mainly via CB1 cannabinoid and vanilloid receptors. However, effects in the pulmonary circulation are unknown. Using the isolated, ventilated, buffer-perfused rabbit lung, we have shown that the endocannabinoids arachidonyl ethanolamide (anandamide) and 2-arachidonyl glycerol (2-AG) dose-dependently increase pulmonary arterial pressure (+19.9 +/- 3.4 mmHg, 5 microM, and +39.5 +/- 10.8 mmHg, 0.4 microM, respectively). 2-AG induced lung edema. The CB1 receptor antagonist AM-251 (0.1 and 5 microM) and the VR1 vanilloid receptor antagonist capsazepine (10 microM) failed to reduce anandamide's effects. The metabolically stable anandamide and 2-AG analogs R-methanandamide and noladin ether, Delta9-tetrahydrocannabinol, and the synthetic cannabinoid HU-210, which is no arachidonic acid product, were without effect. The unspecific cyclooxygenase (COX) inhibitor aspirin (100 microM, P < 0.001) and the specific COX-2 inhibitor nimesulide (10 microM, P < 0.01) completely prevented pulmonary hypertension after 5 microM anandamide. COX-2 RNA was detected in rabbit lungs. The synthetic thromboxane receptor antagonist SQ 29,548 was without effect, but the specific EP1 prostanoid receptor antagonist SC-19220 (100 microM) inhibited the pressure increase after anandamide (P < 0.05). PCR analysis detected fatty acid amidohydrolase (FAAH), an enzyme that degrades endocannabinoids, in rabbit lung tissue. Furthermore, the specific FAAH inhibitor methyl arachidonyl fluorophosphonate (0.1 microM) blocked pressure effects of anandamide (P < 0.01). Finally, anandamide (99 +/- 55 pmol/g) and 2-AG (19.6 +/- 8.4 nmol/g) were found in native lungs. We conclude that anandamide increases pulmonary arterial pressure via COX-2 metabolites following enzymatic degradation by FAAH into arachidonic acid products.

Prostaglandin E2 EP2 and EP4 receptor activation mediates cAMP-dependent hyperpolarization and exocytosis of renin in juxtaglomerular cells

PGE(2) and PGI(2) stimulate renin secretion and cAMP accumulation in juxtaglomerular granular (JG) cells. We addressed, at the single-cell level, the receptor subtypes and intracellular transduction mechanisms involved. Patch clamp was used to determine cell capacitance (C(m)), current, and membrane voltage in response to PGE(2), EP2 and EP4 receptor agonists, and an IP receptor agonist. PGE(2) (0.1 micromol/l) increased C(m) significantly, and the increase was abolished by intracellular application of the protein kinase A antagonist Rp-8-CPT-cAMPS. EP2-selective ligands butaprost (1 micromol/l), AE1-259-01 (1 nmol/l), EP4-selective agonist AE1-329 (1 nmol/l), and IP agonist iloprost (1 micromol/l) significantly increased C(m) mediated by PKA. The EP4 antagonist AE3-208 (10 nmol/l) blocked the effect of EP4 agonist but did not alter the response to PGE(2). Application of both EP4 antagonist and EP2-antagonist AH-6809 abolished the effects of PGE(2) on C(m) and current. EP2 and EP4 ligands stimulated cAMP formation in JG cells. PGE(2) rapidly stimulated renin secretion from superfused JG cells and diminished the membrane-adjacent granule pool as determined by confocal microscopy. The membrane potential hyperpolarized significantly after PGE(2), butaprost, AE1-329 and AE1-259 and outward current was augmented in a PKA-dependent fashion. PGE(2)-stimulated outward current, but not C(m) change, was abolished by the BK(Ca) channel inhibitor iberiotoxin (300 nmol/l). EP2 and EP4 mRNA was detected in sampled JG cells, and the preglomerular and glomerular vasculature was immunopositive for EP4. Thus IP, EP2, and EP4 receptors are associated with JG cells, and their activation leads to rapid PKA-mediated exocytotic fusion and release of renin granules.

Mutant G-protein-coupled receptors as a cause of human diseases

G-protein-coupled receptors (GPCR) are involved in directly and indirectly controlling an extraordinary variety of physiological functions. Their key roles in cellular communication have made them the target for more than 60% of all currently prescribed drugs. Mutations in GPCR can cause acquired and inherited diseases such as retinitis pigmentosa (RP), hypo- and hyperthyroidism, nephrogenic diabetes insipidus, several fertility disorders, and even carcinomas. To date, over 600 inactivating and almost 100 activating mutations in GPCR have been identified which are responsible for more than 30 different human diseases. The number of human disorders is expected to increase given the fact that over 160 GPCR have been targeted in mice. Herein, we summarize the current knowledge relevant to understanding the molecular basis of GPCR function, with primary emphasis on the mechanisms underlying GPCR malfunction responsible for different human diseases.

Vasoconstriction induced by activation of EP1 and EP3 receptors in human lung: effects of ONO-AE-248, ONO-DI-004, ONO-8711 or ONO-8713

This study investigated the effects and selectivity of ONO-AE-248, ONO-DI-004, ONO-8711 and ONO-8713 on EP1 and EP3 receptors in human pulmonary vessels. The prostanoid receptors involved in the vasoconstriction of human pulmonary arteries (HPA) are TP and EP3 whereas in pulmonary veins (HPV), this response is associated with TP and EP1. The experiments were performed in presence of BAY u3405 (TP antagonist). ONO-DI-004 (EP1 agonist) and ONO-AE-248 (EP3 agonist), exhibited little or no activity in HPV whereas contractions were induced in HPA with ONO-AE-248. In HPV, the contractions produced with sulprostone (EP1,3 agonist) were blocked in a non competitive manner by both EP1 antagonists (ONO-8711, 30 microM; ONO-8713, 10 microM). The involvement of EP1 mediated contraction in HPV was also observed during the vasorelaxations induced with PGE1 and 5-cis-carba-PGI2. In pre-contracted HPV treated with AH6809 (30 microM; EP1 antagonist) the PGE1 vasorelaxations were potentiated, while unchanged in HPA. These results demonstrate the selectivity of ONO-AE-248 for the EP3 receptor in HPA, ONO-DI-004 was ineffective on the EP1 receptor present in HPV while ONO-8713 was the more potent EP1 antagonist used in this tissue.

Contribution of prostaglandin EP(2) receptors to renal microvascular reactivity in mice

The present studies were performed to determine the contribution of EP(2) receptors to renal hemodynamics by examining afferent arteriolar responses to PGE(2), butaprost, sulprostone, and endothelin-1 in EP(2) receptor-deficient male mice (EP(2)-/-). Afferent arteriolar diameters averaged 17.8 +/- 0.8 microm in wild-type (EP(2)+/+) mice and 16.7 +/- 0.7 microm in EP(2)-/- mice at a renal perfusion pressure of 100 mmHg. Vessels from both groups of mice responded to norepinephrine (0.5 microM) with similar 17-19% decreases in diameter. Diameters of norepinephrine-preconstricted afferent arterioles increased by 7 +/- 2 and 20 +/- 6% in EP(2)+/+ mice in response to 1 microM PGE(2) and 1 microM butaprost, respectively. In contrast, afferent arteriolar diameter of EP(2)-/- mice decreased by 13 +/- 3 and 16 +/- 6% in response to PGE(2) and butaprost. The afferent arteriolar vasoconstriction to butaprost in EP(2)-/- mice was eliminated by angiotensin-converting enzyme inhibition. Sulprostone, an EP(1) and EP(3) receptor ligand, decreased afferent arteriolar diameter in both groups; however, the vasoconstriction in the EP(2)-/- mice was greater than in the EP(2)+/+ mice. Endothelin-1-mediated afferent arteriolar diameter responses were enhanced in EP(2)-/- mice. Afferent arteriolar diameter decreased by 29 +/- 7% in EP(2)-/- and 12 +/- 7% in EP(2)+/+ mice after administration of 1 nM endothelin-1. These results demonstrate that the EP(2) receptor mediates a portion of the PGE(2) afferent arteriolar vasodilation and buffers the renal vasoconstrictor responses elicited by EP(1) and EP(3) receptor activation as well as endothelin-1.

Opposite effects of cyclooxygenase-1 and -2 activity on the pressor response to angiotensin II

Therapeutic use of cyclooxygenase-inhibiting (COX-inhibiting) nonsteroidal antiinflammatory drugs (NSAIDs) is often complicated by renal side effects including hypertension and edema. The present studies were undertaken to elucidate the roles of COX1 and COX2 in regulating blood pressure and renal function. COX2 inhibitors or gene knockout dramatically augment the pressor effect of angiotensin II (Ang II). Unexpectedly, after a brief increase, the pressor effect of Ang II was abolished by COX1 deficiency (either inhibitor or knockout). Ang II infusion also reduced medullary blood flow in COX2-deficient but not in control or COX1-deficient animals, suggesting synthesis of COX2-dependent vasodilators in the renal medulla. Consistent with this, Ang II failed to stimulate renal medullary prostaglandin E(2) and prostaglandin I(2) production in COX2-deficient animals. Ang II infusion normally promotes natriuresis and diuresis, but COX2 deficiency blocked this effect. Thus, COX1 and COX2 exert opposite effects on systemic blood pressure and renal function. COX2 inhibitors reduce renal medullary blood flow, decrease urine flow, and enhance the pressor effect of Ang II. In contrast, the pressor effect of Ang II is blunted by COX1 inhibition. These results suggest that, rather than having similar cardiovascular effects, the activities of COX1 and COX2 are functionally antagonistic.

Cloning and expression of the rabbit prostaglandin EP2 receptor

BACKGROUND

Prostaglandin E2 (PGE2) has multiple physiologic roles mediated by G protein coupled receptors designated E-prostanoid, or "EP" receptors. Evidence supports an important role for the EP2 receptor in regulating fertility, vascular tone and renal function.

RESULTS

The full-length rabbit EP2 receptor cDNA was cloned. The encoded polypeptide contains 361 amino acid residues with seven hydrophobic domains. COS-1 cells expressing the cloned rabbit EP2 exhibited specific [3H]PGE2 binding with a Kd of 19.1 +/- 1.7 nM. [3H]PGE2 was displaced by unlabeled ligands in the following order: PGE2>>PGD2=PGF2alpha=iloprost. Binding of [3H]PGE2 was also displaced by EP receptor subtype selective agonists with a rank order of affinity consistent with the EP2 receptor (butaprost>AH13205>misoprostol>sulprostone). Butaprost free acid produced a concentration-dependent increase in cAMP accumulation in rabbit EP2 transfected COS-1 cells with a half-maximal effective concentration of 480 nM. RNase protection assay revealed high expression in the ileum, spleen, and liver with lower expression in the kidney, lung, heart, uterus, adrenal gland and skeletal muscle. In situ hybridization localized EP2 mRNA to the uterine endometrium, but showed no distinct localization in the kidney. EP2 mRNA expression along the nephron was determined by RT-PCR and its expression was present in glomeruli, MCD, tDL and CCD. In cultured cells EP2 receptor was not detected in collecting ducts but was detected in renal interstitial cells and vascular smooth muscle cells. EP2 mRNA was also detected in arteries, veins, and preglomerular vessels of the kidney.

CONCLUSION

EP2 expression pattern is consistent with the known functional roles for cAMP coupled PGE2 effects in reproductive and vascular tissues and renal interstitial cells. It remains uncertain whether it is also expressed in renal tubules.

Developmental expression of functional cyclooxygenases in zebrafish

Study of the cyclooxygenases (COXs) has been limited by the role of COX-2 in murine reproduction and renal organogenesis. We sought to characterize COX expression and function in zebrafish (z). Full-length cDNAs of zCOX-1 and zCOX-2 were cloned and assigned to conserved regions of chromosomes 5 and 2, respectively. The deduced proteins are 67% homologous with their human orthologs. Prostaglandin (PG) E(2) is the predominant zCOX product detected by mass spectrometry. Pharmacological inhibitors demonstrate selectivity when directed against heterologously expressed zCOX isoforms. Zebrafish thrombocyte aggregation ex vivo and hemostasis in vivo are sensitive to inhibition of zCOX-1, but not zCOX-2. Both zCOXs were widely expressed during development, and knockdown of zCOX-1 causes growth arrest during early embryogenesis. zCOX-1 is widely evident in the embryonic vasculature, whereas zCOX-2 exhibits a more restricted pattern of expression. Both zCOX isoforms are genetically and functionally homologous to their mammalian orthologs. The zebrafish affords a tractable model system for the study of COX biology and development.

EP2 receptors mediate airway relaxation to substance P, ATP, and PGE2

Substance P (SP) and ATP evoke transient, epithelium-dependent relaxation of constricted mouse tracheal smooth muscle. Relaxation to either SP or ATP is blocked by indomethacin, but the specific eicosanoid(s) involved have not been definitively identified. SP and ATP are reported to release PGE2 from airway epithelium in other species, suggesting PGE2 as a likely mediator in epithelium-dependent airway relaxation. Using mice homozygous for a gene-targeted deletion of the EP2 receptor [EP2(-/-)], one of the PGE2 receptors, we tested the hypothesis that PGE2 is the primary mediator of relaxation to SP or ATP. Relaxation in response to SP or ATP was significantly reduced in tracheas from EP2(-/-) mice. There were no differences between EP2(-/-) and wild-type tracheas in their physical dimensions, contraction to ACh, or relaxation to isoproterenol, thus ruling out any general alterations of smooth muscle function. There were also no differences between EP2(-/-) and wild-type tracheas in basal or stimulated PGE2 production. Exogenous PGE2 produced significantly less relaxation in EP2(-/-) tracheas compared with the wild type. Taken together, this experimental evidence supports the following two conclusions: EP2 receptors are of primary importance in airway relaxation to PGE2 and relaxation to SP or ATP is mediated through PGE2 acting on EP2 receptors.

G protein-coupled prostanoid receptors and the kidney

Renal cyclooxygenase 1 and 2 activity produces five primary prostanoids: prostaglandin E2, prostaglandin F2alpha, prostaglandin I2, thromboxane A2, and prostaglandin D2. These lipid mediators interact with a family of distinct G protein-coupled prostanoid receptors designated EP, FP, IP, TP, and DP, respectively, which exert important regulatory effects on renal function. The intrarenal distribution of these prostanoid receptors has been mapped, and the consequences of their activation have been partially characterized. FP, TP, and EP1 receptors preferentially couple to an increase in cell calcium. EP2, EP4, DP, and IP receptors stimulate cyclic AMP, whereas the EP3 receptor preferentially couples to Gi, inhibiting cyclic AMP generation. EP1 and EP3 mRNA expression predominates in the collecting duct and thick limb, respectively, where their stimulation reduces NaCl and water absorption, promoting natriuresis and diuresis. The FP receptor is highly expressed in the distal convoluted tubule, where it may have a distinct effect on renal salt transport. Although only low levels of EP2 receptor mRNA are detected in the kidney and its precise intrarenal localization is uncertain, mice with targeted disruption of the EP2 receptor exhibit salt-sensitive hypertension, suggesting that this receptor may also play an important role in salt excretion. In contrast, EP4 receptor mRNA is predominantly expressed in the glomerulus, where it may contribute to the regulation of glomerular hemodynamics and renin release. The IP receptor mRNA is highly expressed near the glomerulus, in the afferent arteriole, where it may also dilate renal arterioles and stimulate renin release. Conversely, TP receptors in the glomerulus may counteract the effects of these dilator prostanoids and increase glomerular resistance. At present there is little evidence for DP receptor expression in the kidney. These receptors act in a concerted fashion as physiological buffers, protecting the kidney from excessive functional changes during periods of physiological stress. Nonsteroidal anti-inflammatory drug (NSAID)-mediated cyclooxygenase inhibition results in the loss of these combined effects, which contributes to their renal effects. Selective prostanoid receptor antagonists may provide new therapeutic approaches for specific disease states.

Prostanoid receptors: subtypes and signaling

Cyclooxygenases metabolize arachidonate to five primary prostanoids: PGE(2), PGF(2 alpha), PGI(2), TxA(2), and PGD(2). These autacrine lipid mediators interact with specific members of a family of distinct G-protein-coupled prostanoid receptors, designated EP, FP, IP, TP, and DP, respectively. Each of these receptors has been cloned, expressed, and characterized. This family of eight prostanoid receptor complementary DNAs encodes seven transmembrane proteins which are typical of G-protein-coupled receptors and these receptors are distinguished by their ligand-binding profiles and the signal transduction pathways activated on ligand binding. Ligand-binding selectivity of these receptors is determined by both the transmembrane sequences and amino acid residues in the putative extracellular-loop regions. The selectivity of interaction between the receptors and G proteins appears to be mediated at least in part by the C-terminal tail region. Each of the EP(1), EP(3), FP, and TP receptors has alternative splice variants described that alter the coding sequence in the C-terminal intracellular tail region. The C-terminal variants modulate signal transduction, phosphorylation, and desensitization of these receptors, as well as altering agonist-independent constitutive activity.

Localization of prostaglandin E(2) EP2 and EP4 receptors in the rat kidney

We investigated the localization of cAMP-coupled prostaglandin E(2) EP2 and EP4 receptor expression in the rat kidney. EP2 mRNA was restricted to the outer and inner medulla in rat kidney, as determined by RNase protection assay. RT-PCR analysis of microdissected resistance vessels and nephron segments showed EP2 expression in descending thin limb of Henle's loop (DTL) and in vasa recta of the outer medulla. The EP4 receptor was expressed in distal convoluted tubule (DCT) and cortical collecting duct (CCD) in preglomerular vessels, and in outer medullary vasa recta. Butaprost, an EP2 receptor-selective agonist, dose dependently raised cAMP levels in microdissected DTL and outer medullary vasa recta specimens but had no effect in EP2-negative outer medullary collecting duct segments. Dietary salt intake did not alter EP2 expression in the kidney medulla. These results suggest that PGE(2) may act in the resistance vessels and in the DTL and DCT-CCD segments as a paracrine, cAMP-dependent regulator of vascular resistance and tubular transport, respectively.

The prostaglandin E2 EP1 receptor mediates pain perception and regulates blood pressure

The lipid mediator prostaglandin E2 (PGE2) has diverse biological activity in a variety of tissues. Four different receptor subtypes (EP1-4) mediate these wide-ranging effects. The EP-receptor subtypes differ in tissue distribution, ligand-binding affinity, and coupling to intracellular signaling pathways. To identify the physiological roles for one of these receptors, the EP1 receptor, we generated EP1-deficient (EP1-/-) mice using homologous recombination in embryonic stem cells derived from the DBA/1lacJ strain of mice. The EP1-/- mice are healthy and fertile, without any overt physical defects. However, their pain-sensitivity responses, tested in two acute prostaglandin-dependent models, were reduced by approximately 50%. This reduction in the perception of pain was virtually identical to that achieved through pharmacological inhibition of prostaglandin synthesis in wild-type mice using a cyclooxygenase inhibitor. In addition, systolic blood pressure is significantly reduced in EP1 receptor-deficient mice and accompanied by increased renin-angiotensin activity, especially in males, suggesting a role for this receptor in cardiovascular homeostasis. Thus, the EP1 receptor for PGE2 plays a direct role in mediating algesia and in regulation of blood pressure.