Prostaglandin receptor EP2 mediates PGE2 stimulated hypercalcemia in mice in vivo

Prostaglandin E2 (PGE2) can stimulate bone resorption by a cyclic AMP-dependent pathway. Two PGE2 receptors, EP2 and EP4 have been shown to play a role in PGE2 stimulation of osteoclast formation. In primary osteoblastic cell cultures from EP2 wild type (EP2 +/+) mice, PGE2 (0.1 microM) increased cyclic AMP production 3.5-fold, but PGE2 had no effect on cells from mice in which the EP2 receptor had been deleted (EP2 -/-). To examine the role of the EP2 receptor in the resorption response in vivo we injected PGE2 in EP2 -/- mice, and compared them with EP2 +/+ mice. Injection of PGE2 (3 mg/kg, four times daily for three days) in 9- to 12-month-old male mice on a 129 SvEv background increased serum calcium from 9.8 +/- 0.5 to 10.7 +/- 0.3 mg/dl (P < 0.01) in EP2 +/+ mice but not in EP2 -/- mice (10.1 +/- 0.3 vs. 10.2 +/- 0.3 mg/dl). PGE2 injection (6 mg/kg twice a day for three days) in 3-4 month old male mice on a C57 BL/6 X 129 SvEv background increased calcium from 8.2 +/- 0.1 to 9.0 +/- 0.3 mg/dl (P < 0.05) in EP2 +/+ mice but had no effect in EP2-/- mice (8.4 +/- 0.1 vs. 8.3 +/- 0.2 mg/dl). Injection of PGE2 over the calvariae of EP2 +/+ and EP2-/- mice increased the expression of receptor activator of nuclear factor kappaB ligand (RANKL) both locally and in the tibia, but RANKL responses were lower in EP2 -/- mice. We conclude that EP2 receptor plays a role in the hypercalcemic response to PGE2. This impaired response in EP2 -/- mice may be due to decreased ability to stimulate cyclic AMP and in part, to a smaller increase in the expression of RANKL mRNA.     

Hemodilution mediates hemodynamic changes during acute expansion in unanesthetized rats

Studies were carried out to determine the relative importance of volume and hemodilution on hemodynamic adjustments to acute volume expansion. Systemic and renal hemodynamics were monitored in unanesthetized and unrestrained rats during progressive and equivalent blood volume expansion with saline (Sal; 1, 2, and 4% body wt), 7% BSA solution (0.35, 0.7, and 1.4% body wt), and reconstituted whole blood from donor rats (WBL; 0.35, 0.7, and 1.4% body wt). Mean arterial pressure remained unchanged in Sal and BSA but increased progressively in WBL-expanded rats (from 92 to 106 mmHg after maximal expansion). In Sal and BSA-expanded rats, cardiac output (CO) and renal blood flow (RBF) increased (CO: Sal from 19 to 20, 22, and 25; BSA from 21 to 23, 27, and 31; RBF: Sal from 1.6 to 1.8, 2.2, and 2.5; BSA from 2 to 2.4, 2.7, and 3.1 ml. min(-1). 100 g body wt(-1)), whereas total peripheral (TPR) and renal vascular (RVR) resistance decreased in parallel with the expansions. After expansion with WBL, CO increased progressively but less extensively than in cell-free expanded rats (21 to 22, 24, and 26 ml. min(-1). 100 g body wt(-1)), whereas TPR and RVR remained unchanged. Systemic hematocrit (Hct) decreased approximately the same after expansion with Sal or BSA solutions but remained unchanged after expansion with WBL. Isovolemic hemodilution to Hct levels comparable to those seen after maximal expansion with cell-free solutions also reduced SVR and RVR, although less extensively. These findings suggest that in unanesthetized rats hemodilution plays a major role in the systemic and renal hemodynamics during expansion.     

EP(2) receptor mediates bronchodilation by PGE(2) in mice.

PGE(2) is an important cyclooxygenase product that modulates airway inflammatory and smooth muscle responses. Signal transduction is mediated by four EP receptor subtypes that cause distinct effects on cell metabolism. To determine the role of EP(2) receptor activation, we produced a mouse lacking the EP(2) receptor by targeted gene disruption. The effect of aerosolized PGE(2) and other agonists was measured using barometric plethysmography and by measurements of lung resistance in mechanically ventilated mice. Inhalation of PGE(2) inhibited methacholine responses in wild-type but not in mice lacking the EP(2) receptor [EP(2)(-/-)]. After airway constriction was induced by methacholine aerosol, PGE(2) reduced the airway constriction enhanced pause in wild-type mice (from 0.88 +/- 0.15 to 0.55 +/- 0.06) but increased it in EP(2)(-/-) mice (from 0.73 +/- 0. 08 to 1.27 +/- 0.19). Similar results were obtained in mechanically ventilated mice. These data indicate that the EP(2) receptor mediates the bronchodilation effect of PGE(2).     

Losartan decreases glomerular filtration rate in isolated perfused porcine slaughterhouse kidneys

We investigated whether Losartan, an angiotensin II (Ang II) AT1 receptor antagonist, decreases renal vascular resistance (RVR) and increases glomerular filtration rate (GFR) in isolated perfused porcine slaughterhouse kidneys (11 control experiments and 11 Losartan experiments with 7.5mg Losartan in the preservation solution and 100(g/minute Losartan infused during perfusion). With perfusion, plasma renin activity (PRA) increased markedly from 3 +/- 1 to 90 +/- 17 ng Ang I/ml/h (control), and from 4 +/- 1 to 70 +/- 8 ng Ang I/ml/h (Losartan), plasma Ang II increased from 86 +/- 63 to 482 +/- 111 pg/ml (control), and from 73 +/- 42 to 410 +/- 91 pg/ml (Losartan). The GFR was decreased in Losartan experiments as compared with control experiments (5 +/- 1 versus 10 +/- 2 ml/min/100g kidney wt; p < 0.05). The RVR was the same in both groups (0.2 +/- 0.01 mm Hg/100g kidney wt/min/ml). Tubular sodium reabsorption was decreased in Losartan experiments as compared with control experiments (0.7 +/- 0.1 versus 1.4 +/- 0.3 mmol/min/100g kidney wt). Overall, Losartan accentuated pathophysiological signs of acute renal failure. Although other drugs have to be investigated, these results suggest that porcine slaughterhouse kidneys could be useful as a tool for research in areas such as transplantation and intensive-care medicine.     

Renal interstitial fluid ATP responses to arterial pressure and tubuloglomerular feedback activation during calcium channel blockade

A close relationship between changes in renal interstitial fluid (RIF) ATP concentrations and renal autoregulatory or tubuloglomerular feedback (TGF)-dependent changes in renal vascular resistance (RVR) has been demonstrated, but it has not been determined whether the changes in RIF ATP are a consequence or the cause of the changes in RVR. The present study was performed in anesthetized dogs to assess the changes in RIF ATP following changes in renal arterial pressure (RAP) or stimulation of the TGF mechanism under conditions where changes in RVR were prevented by nifedipine, a calcium channel blocker. RIF ATP levels were measured by using microdialysis probes. Intra-arterial infusion of nifedipine (0.36 microg x kg(-1) x min(-1)) increased renal blood flow (RBF: from 4.49 +/- 0.27 to 5.34 +/- 0.39 ml x min(-1) x g(-1)) and glomerular filtration rate (GFR: from 0.84 +/- 0.07 to 1.09 +/- 0.11 ml x min(-1) x g(-1)). Under conditions of nifedipine infusion, autoregulatory adjustments in RBF, GFR, and RVR were not observed during stepwise reductions in RAP within the autoregulatory range (from 135 +/- 7 to 76 +/- 1 mmHg, n = 7). Furthermore, stimulation of the TGF mechanism with intra-arterial infusion of acetazolamide (100 microg x kg(-1) x min(-1)) did not alter RBF, GFR, and RVR (n = 7). During treatment with nifedipine, RIF ATP levels were significantly decreased in response to reductions in RAP (10.7 +/- 0.7, 5.8 +/- 0.7 and 2.8 +/- 0.3 nmol/l at 135 +/- 7, 101 +/- 4, and 76 +/- 1 mmHg, n = 7) and increased by acetazolamide infusion (from 8.8 +/- 0.8 to 17.0 +/- 1.8 nmol/l, n = 7). These results are similar to those that occurred in dogs not treated with nifedipine and thus demonstrate that the changes in RIF ATP can occur in the absence of autoregulatory or TGF-mediated changes in RVR. The data provide further support to the hypothesis that RIF ATP contributes to adjustments in RVR associated with renal autoregulation and changes in activity of the TGF mechanism.     

Tetradecylthioacetic acid downregulates cyclooxygenase 2 in the renal cortex of two-kidney, one-clip hypertensive rats

The effect of tetradecylthioacetic acid (TTA) on the cyclooxygenase (COX) system was investigated in two-kidney, one-clip (2K1C) hypertensive rats. The systolic blood pressure (BP) was increased 6 wk after clipping to 183 +/- 4 vs.127 +/- 3 mmHg in TTA-treated 2K1C rats. The COX1 protein expression was not affected either by the 2K1C procedure or by TTA treatment. COX2 expression was upregulated in both kidneys, but to a greater extent in the clipped kidney. COX2 activity was 16 +/- 3% in control and 38 +/- 2% (P < 0.001) in the clipped kidney, and COX2 protein expression was 1.3 +/- 0.04 in control and 1.6 +/- 0.12 in the clipped kidney (P = 0.006). TTA reduced COX2 activity to control levels. Subcutaneously infusion of a COX2 inhibitor did not reduce BP. Peroxisome proliferator-activated receptors (PPARs) were detected in both kidneys, and PPARdelta was upregulated in the nonclipped kidney after TTA treatment. PGE2 in renal cortex was increased in 2K1C (31 +/- 0.3 in the clipped and 28 +/- 0.2 pg/ml nonclipped kidney, P < 0.001 compared with control). TTA lowered the PGE2 to control levels. Renal blood flow (RBF) response to exogenous ANG II injected in the control and nonclipped kidney was exaggerated after indomethacin treatment but unchanged in the nonclipped kidney of the K1C TTA group. Overall, these results indicate that, after 6 wk of treatment, TTA downregulated the COX2 activity, which have potentially important effects on the regulation of renal hemodynamics but does not explain TTAs ability to lower BP.     

Effect of saline infusion on kidney and collecting duct function in atrial natriuretic peptide (ANP) gene "knockout" mice.

Atrial natriuretic peptide (ANP) is thought to play a role in renal regulation of salt balance by reducing tubular reabsorption of sodium and chloride. Therefore, in the chronic absence of this hormone, a defect of salt excretion should be evident. We used an ANP gene deletion model to test this premise. F2 homozygous mutant mice (-/-) and their wild-type littermates (+/+) were fed an 8% NaCl diet prior to an acute infusion of isotonic saline. Arterial blood pressures, renal excretions of salt and water, as well as collecting duct transport of fluid and electrolytes were measured. Pressures were significantly higher in -/- compared with +/+ mice (139 +/- 4 vs. 101 +/- 2 mmHg; 1 mmHg = 133.3 Pa). There was no difference in glomerular filtration rate (-/- = 0.84 +/- 0.06; +/+ = 0.81 +/- 0.04 mL x min(-1) x g(-1) kidney weight). In the collecting duct, sodium and chloride reabsorptions were significantly higher in the -/- group than in the +/+ group. As a result, natriuresis and chloruresis were relatively reduced (U(Na)V: -/- = 8.6 +/- 1.1; +/+ = 14.0 +/- 1.1; U(Cl)V: -/- = 10.1 +/- 1.4; +/+ = 16.0 +/- 1.1 micromol x min(-1) x g(-1) kidney weight). We conclude that the absence of endogenous ANP activity in mice on a high-salt diet subjected to acute saline infusion causes inappropriately high reabsorption of sodium and chloride in the medullary collecting duct, resulting in a relative defect in renal excretory capacity for salt.     

Role of intrarenal alpha(2)-adrenoceptors in the renal responses to xylazine in rats

This study examined the contribution of intrarenal alpha(2)-adrenoceptor mechanisms to the enhanced urine flow rate (V) and urinary sodium excretion (U(Na)V) responses in ketamine-xylazine-anesthetized rats. Ten minutes after left renal artery (LRA) injection, the alpha(2)-adrenoceptor antagonist yohimbine (5 microg) significantly decreased V from 58 +/- 8 to 35 +/- 7 microl. min(-1). g kidney wt(-1) and U(Na)V from 2.8 +/- 0.4 to 2.1 +/- 0.4 microeq. min(-1). g kidney wt(-1) without altering right kidney function. The renal effects of the LRA injection of yohimbine were completely abolished in chronic bilaterally renal-denervated (RDNX) rats. In RDNX rats, a higher LRA dose of yohimbine (15 microg) significantly reduced left and right kidney V, with no effects on U(Na)V. In separate bladder-catheterized rats, yohimbine (0.5 mg/kg), 20 min after intravenous injection, significantly decreased V from 63 +/- 9 to 13 +/- 2 microl. min(-1). g kidney wt(-1 )and U(Na)V from 4.5 +/- 0.5 to 1.1 +/- 0.1 microeq. min(-1). g kidney wt(-1). In RDNX rats, this dose of yohimbine reduced V and U(Na)V, but the magnitude was blunted compared with intact rats. In contrast, 0.1 mg/kg iv yohimbine significantly reduced V and U(Na)V to similar magnitudes in intact and RDNX groups. Together, these findings indicate that intravenous xylazine acts by renal nerve-dependent and -independent mechanisms to enhance renal excretory function in ketamine-anesthetized rats. Because the effects of the LRA dose of yohimbine were abolished in renal-denervated animals, it appears that xylazine has a direct renal action to augment the renal excretion of water and sodium via a presynaptic alpha(2)-adrenoceptor pathway that inhibits the release of neurotransmitters from renal sympathetic nerve terminals.     

Acetylcholine chloride and renal hemodynamics during postnatal maturation in conscious lambs.

To test the hypothesis that acetylcholine-induced relaxation of the renal artery decreases with postnatal age, we measured parameters of renal hemodynamics before and for 35 s after aortic suprarenal injection of acetylcholine in conscious, chronically instrumented lambs aged approximately 1 wk (n = 5) and approximately 6 wk (n = 5). Acetylcholine was administered in one of five doses ranging from 0 to 10 mg/kg body wt; doses were administered randomly, in the same volume. There were significant age- and dose-dependent changes in renal vascular resistance after acetylcholine administration, such that the response was greater in 1-wk-old lambs. After the highest dose tested, renal vascular resistance decreased by 13.6 +/- 7.3 (SD) mmHg. ml(-1). min. g kidney wt in 1-wk-old lambs and by 9.1 +/- 3.2 mmHg. ml(-1). min. g kidney wt in 6-wk-old lambs at 35 s. We also observed a transient renal vasoconstriction before the renal vasodilatation in 6-wk-old lambs but not in 1-wk-old animals. These data provide the first age- and dose-dependent effects of exogenous administration of acetylcholine on renal hemodynamics during maturation in conscious animals.     

Prostaglandin E(2) receptors, EP2 and EP4, differentially modulate TNF-alpha and IL-6 production induced by lipopolysaccharide in mouse peritoneal neutrophils

The expression and function of prostaglandin (PG) E(2) receptors were examined in mouse neutrophils exudated into the peritoneal cavity by casein treatment. Expressions of the EP2 and EP4 receptors were detected in neutrophils by Northern blot, but those of EP1 and EP3 receptors were not detected by RT-PCR. EP2-selective agonist, ONO-AE1-259, and EP4-selective agonist, ONO-AE1-329, stimulated cAMP formation in the cells. PGE(2) affected the TNF-alpha and IL-6 production in lipopolysaccharide (LPS)-treated neutrophils; it suppressed the TNF-alpha production and enhanced the IL-6 production. The PGE(2) effects were mimicked by dibutyryl cAMP. This is the first study of the enhancement of IL-6 production by cAMP-elevating reagents in neutrophils. Using neutrophils from EP2- and EP4-deficient mice in combination with EP2- and EP4-selective agonists, it was found that the augmentation of IL-6 was mediated mainly by the EP2 receptor and the suppression of TNF-alpha by the EP4 receptor and partially by the EP2 receptor. These findings indicate that casein-induced peritoneal neutrophils express Gs-coupled PGE(2) receptors, EP2 and EP4, which might differentially regulate the LPS-induced production of TNF-alpha and IL-6.     

Increased severity of renal impairment in nephritic mice lacking the EP1 receptor

In experimental glomerulonephritis, inhibition of renal prostaglandin (PG) synthesis by nonsteroidal-anti-inflammatory drugs (NSAIDs) moderates proteinuria, yet can induce harmful effects on renal blood flow and Na+ - K+ - water balance thereby implicating 1 or more prostanoid receptor subtypes. We investigated the role of the PGE2 EP1 receptor in nephritis since it is expressed in the glomerulus, collecting duct and vasculature in which its activity might contribute to adaptive or maladaptive responses. Accordingly, a mouse model of accelerated antiglomerular basement membrane (anti-GBM) nephrotoxic serum (NTS) nephritis was induced in mice with targeted-deletion of the EP1 receptor (EP1-/-). Proteinuria was similar between wild-type (wt) and EP1-/- NTS groups, thus negating a role for this subtype in modulating the glomerular permeability barrier in this model of anti-GBM NTS. However, overall renal damage was more acute in NTS EP1-/- mice, as evidenced by the degree of glomerular mesangial matrix expansion and the frequency of tubular dilatations. These changes in renal pathology were accompanied by stronger impairment of renal function in NTS EP1-/- mice, such that levels of serum creatinine, urea, Na+, and K+ were each significantly higher than those observed in NTS wt mice. Lastly, compared with wt mice, induction of NTS more severely reduced urine osmolality and body mass in EP1-/- mice. Taken together, the increased renal impairment seen in NTS EP1-/- mice suggests that the EP1 subtype plays a compensatory role in the context of acute nephritis.     

A Maladaptive Role for EP4 Receptors in Mouse Mesangial Cells

Roles of the prostaglandin E2 E-prostanoid 4 receptor (EP4) on extracellular matrix (ECM) accumulation induced by TGF-β1 in mouse glomerular mesangial cells (GMCs) remain unknown. Previously, we have identified that TGF-β1 stimulates the expression of FN and Col I in mouse GMCs. Here we asked whether stimulation of EP4 receptors would exacerbate renal fibrosis associated with enhanced glomerular ECM accumulation. We generated EP4^Flox/Flox and EP4^+/− mice, cultured primary WT, EP4^Flox/Flox and EP4^+/− GMCs, AD-EP4 transfected WT GMCs (EP4 overexpression) and AD-Cre transfected EP4^Flox/Flox GMCs (EP4 deleted). We found that TGF-β1-induced cAMP and PGE2 synthesis decreased in EP4 deleted GMCs and increased in EP4 overexpressed GMCs. Elevated EP4 expression in GMCs augmented the coupling of TGF-β1 to FN, Col I expression and COX2/PGE2 signaling, while TGF-β1 induced FN, Col I expression and COX2/PGE2 signaling were down-regulated in EP4 deficiency GMCs. 8 weeks after 5/6 nephrectomy (Nx), WT and EP4^+/− mice exhibited markedly increased accumulation of ECM compared with sham-operated controls. Albuminuria, blood urea nitrogen and creatinine (BUN and Cr) concentrations were significantly increased in WT mice as compared to those of EP4^+/− mice. Urine osmotic pressure was dramatically decreased after 5/6 Nx surgery in WT mice as compared to EP4^+/− mice. The pathological changes in kidney of EP4^+/− mice was markedly alleviated compared with WT mice. Immunohistochemical analysis showed significant reductions of Col I and FN in the kidney of EP4^+/− mice compared with WT mice. Collectively, this investigation established EP4 as a potent mediator of the pro-TGF-β1 activities elicited by COX2/PGE2 in mice GMCs. Our findings suggested that prostaglandin E2, acting via EP4 receptors contributed to accumulation of ECM in GMCs and promoted renal fibrosis.     

Mechanisms of the early and late response of the kidney to contralateral nephrectomy.

The immediate (1 day, D1) and late (90 days, D90) effects of unilateral nephrectomy on contralateral renal hemodynamics, and the renal handling of electrolytes and water were investigated in the whole animal. The immediate and late ability of the remnant kidney to autoregulate perfusate flow and glomerular filtration rate (GFR) was studied in the isolated perfused kidney of the rat. In the whole animal, in D1 rats as compared to controls, GFR calculated for a single kidney increased from 0.85 +/- 0.3 to 1.1 +/- 0.2 ml/min (p less than 0.05). In D90 rats GFR increased further and was similar to prenephrectomy GFR (1.4 +/- 0.5 vs. 1.7 +/- 0.5 ml/min, p NS). Urinary prostanoid excretion in 24 h, calculated for one kidney, increased by 50-500% in D1 rats, but returned to prenephrectomy values in D90 rats. In the isolated perfused kidney, decreasing perfusion pressure (PP) from 100 to 70 mmHg did not change the renal vascular resistance (RVR) in control and D90 kidneys, but in D1 kidneys RVR decreased from 8.6 +/- 1.3 to 7 +/- 1.3 mm Hg/ml/min (p less than 0.05). In D90 kidneys RVR was significantly lower as compared to control and D1 kidneys at all perfusion pressures. Decreasing PP from 100 to 70 mm Hg resulted in a significant decrease in perfusion flow in control, D1 and D90 kidneys, while with the increase in PP from 100 to 130 mm Hg the perfusion flow increased significantly in all three kidney groups.(ABSTRACT TRUNCATED AT 250 WORDS)     

Thromboxane receptor blockade improves cyclosporine nephrotoxicity in rats

Cyclosporine A (CyA) nephrotoxicity is associated with impaired renal hemodynamic function and increased production of the vasoconstrictor eicosanoid thromboxane A2 (TxA2). In CyA toxic rats, renal dysfunction can be partially reversed by inhibitors of thromboxane synthase. However, interpretation of these results is complicated since inhibition of thromboxane synthase may cause accumulation of prostaglandin endoperoxides that can act as partial agonists at the TxA2 receptor and may blunt the efficacy of treatment. Furthermore, these endoperoxides may be used as substrate for production of vasodilator prostaglandins causing beneficial effects on hemodynamics which are independent of thromboxane inhibition. To more specifically examine the role of TxA2 in CyA toxicity, we investigated the effects of the thromboxane receptor antagonist GR32191 on renal hemodynamics in a rat model of CyA nephrotoxicity. In this model, administration of CyA resulted in a significant decrease in glomerular filtration rate (GFR) (2.85 +/- 0.26 [CyA] vs 6.82 +/- 0.96 ml/min/kg [vehicle]; p less than 0.0005) and renal blood flow (RBF) (21.65 +/- 2.31 [CyA] vs 31.87 +/- 3.60 ml/min/kg [vehicle]; p less than 0.025). Renal vascular resistance (RVR) was significantly higher in rats given CyA compared to animals treated with CyA vehicle (5.32 +/- 0.55 [CyA] vs. 3.54 +/- 0.24 mm Hg/min/ml/kg [vehicle]; p less than 0.05). These renal hemodynamic alterations were associated with a significant increase in urinary excretion of unmetabolized, "native" thromboxane B2 (TxB2) (103 +/- 18 [CyA] vs 60 +/- 16 pg/hour [vehicle]; p less than 0.05). Only minimal histomorphologic changes were apparent by light microscopic examination of kidneys from both CyA and vehicle treated animals. However, with immunoperoxidase staining, a significantly greater number of cells expressing the rat common leukocyte antigen was found in the renal interstitium of rats given CyA. There was no detectable increase in monocytes/macrophages in the kidneys of CyA toxic animals. In rats treated with CyA, intraarterial infusion of GR32191 at maximally tolerated doses significantly increased GFR and RBF, and decreased RVR. Although both RBF and RVR were restored to levels not different from controls, GFR remained significantly reduced following administration of GR32191. These data suggest that the potent vasoconstrictor TxA2 plays an important role in mediating renal dysfunction in CyA nephrotoxicity. However, other factors may be important in producing nephrotoxicity associated with CyA.     

Prostaglandin E prevents indomethacin-induced gastric and intestinal damage through different EP receptor subtypes

Gastrointestinal ulcerogenic effect of indomethacin is causally related with an endogenous prostaglandin (PG) deficiency, yet the detailed mechanism remains unknown. We examined the effect of various PGE analogues specific to EP receptor subtypes on these lesions in rats and mice, and investigated which EP receptor subtype is involved in the protective action of PGE(2). Fasted or non-fasted animals were given indomethacin s.c. at 35 mg/kg for induction of gastric lesions or 10-30 mg/kg for intestinal lesions, and they were killed 4 or 24 h later, respectively. Various EP agonists were given i.v. 10 min before indomethacin. Indomethacin caused hemorrhagic lesions in both the stomach and intestine. Prior administration of 16,16-dimethyl PGE(2) (dmPGE(2)) prevented the development of damage in both tissues, and the effect in the stomach was mimicked by 17-phenyl PGE2 (EP1), while that in the small intestine was reproduced by ONO-NT-012 (EP3) and ONO-AE-329 (EP4). Butaprost (EP2) did not have any effect on either gastric or intestinal lesions induced by indomethacin. Similar to the findings in rats, indomethacin caused gastric and intestinal lesions in both wild-type and knockout mice lacking EP1 or EP3 receptors. However, the protective action of dmPGE(2) in the stomach was observed in wild-type and EP3 receptor knockout mice but not in mice lacking EP1 receptors, while that in the intestine was observed in EP1 knockout as well as wild-type mice but not in the animals lacking EP3 receptors. These results suggest that indomethacin produced damage in the stomach and intestine in a PGE(2)-sensitive manner, and exogenous PGE(2) prevents gastric and intestinal ulcerogenic response to indomethacin through different EP receptor subtypes; the protection in the stomach is mediated by EP1 receptors, while that in the intestine mediated by EP3/EP4 receptors.     

Prosurvival and antiapoptotic effects of PGE2 in radiation injury are mediated by EP2 receptor in intestine

The biological activities of PGE(2) are mediated through EP receptors (EP(1)-EP(4)), plasma membrane G protein-coupled receptors that differ in ligand binding and signal-transduction pathways. We investigated gastrointestinal EP(2) receptor expression in adult mice before and after radiation injury and evaluated intestinal stem cell survival and crypt epithelial apoptosis after radiation injury in EP(2) null mice. EP(2) was expressed throughout the gut. Intestinal EP(2) mRNA increased fivefold after gamma-irradiation. Crypt survival was diminished in EP(2)-/- mice (4.06 crypts/cross section) compared with wild-type littermates (8.15 crypts/cross section). Radiation-induced apoptosis was significantly increased in EP(2)-/- mice compared with wild-type littermates. Apoptosis was 1.6-fold higher in EP(2) (-/-) mice (5.9 apoptotic cells/crypt) than in wild-type mice (3.5 apoptotic cells/crypt). The EP(2) receptor is expressed in mouse gastrointestinal epithelial cells and is upregulated following radiation injury. The effects of PGE(2) on both crypt epithelial apoptosis and intestinal crypt stem cell survival are mediated through the EP(2) receptor.     

Interaction between prostaglandin E2 and leukotriene D4 on the excretion of electrolytes by the dog kidney in vivo

Recent experiments indicate that prostaglandin E2 potentiates the vasodilatory properties of leukotrienes in the skin microcirculation. The present experiments were undertaken to study the effect of leukotriene D4 and prostaglandin E2 on renal hemodynamics and urinary electrolytes in the dog. Experiments were performed in three groups of anesthetized Mongrel dogs: the first group was studied under hydropenia, whereas the two remaining groups were studied during water diuresis with (Group 3) or without indomethacin (Group 2). LTD4 (100 ng/min) and PGE2 (3 ug/min) were infused in the left renal artery to minimize systemic effects of these compounds. LTD4 alone failed to influence urinary sodium excretion in all 3 groups. In Group 1, urinary sodium increased from 77 +/- 6 to 393 +/- 74 uEq/min during PGE2, and further increased to 511 +/- 52 uEq/min during LTD4 + PGE2. No change occurred in the contralateral right kidney. In this group, glomerular filtration as well as renal plasma flow were not statistically influenced. In Group 2, the same phenomenon was observed for urinary sodium. The combined infusion of LTD4 + PGE2 increased urinary sodium without significant changes in glomerular filtration and renal plasma flow. Finally, in Group 3, indomethacin was shown to reduce the natriuretic effects of LTD4 and PGE2: during PGE2 alone, urinary sodium increased from 90 +/- 14 to 260 +/- 66 uEq/min, and only rose from 80 +/- 10 to 175 +/- 19 uEq/min during the combined infusion of LTD4 and PGE2. In groups 2 and 3, free water clearance was utilized as an index of sodium chloride reabsorption in the thick ascending limb: this parameter increased from 2.35 +/- 0.25 to 4.70 +/- 0.30 ml/min, while urinary volume was increasing from 3.55 +/- 0.25 to 10.05 +/- 0.65 ml/min, during LTD4 + PGE2. Indomethacin, administered in Group 3, (3 mg/kg/hr) again abolished the effect of combined PGE2 + LTD4. These results indicate a potentiating effect of leukotriene D4 on the PGE2-induced natriuresis in the anesthetized dog. These phenomena occurred in the absence of significant changes in renal hemodynamics, therefore suggesting a direct tubular effect of these arachidonic acid metabolites. Finally, the water diuresis experiments suggest a proximal site of action of PGE2 and LTD4.     

Central PGE2 exhibits anxiolytic-like activity via EP1 and EP4 receptors in a manner dependent on serotonin 5-HT1A, dopamine D1 and GABAA receptors

We found that centrally administered prostaglandin (PG) E(2) exhibited anxiolytic-like activity in the elevated plus-maze and open field test in mice. Agonists selective for EP(1) and EP(4) receptors, among four receptor subtypes for PGE(2), mimicked the anxiolytic-like activity of PGE(2). The anxiolytic-like activity of PGE(2) was blocked by an EP(1) or EP(4) antagonist, as well as in EP(4) but not EP(1) knockout mice. Central activation of either EP(1) or EP(4) receptors resulted in anxiolytic-like activity. The PGE(2)-induced anxiolytic-like activity was inhibited by antagonists for serotonin 5-HT(1A), dopamine D(1) and GABA(A) receptors. Taken together, PGE(2) exhibits anxiolytic-like activity via EP(1) and EP(4) receptors, with downstream involvement of 5-HT(1A), D(1) and GABA(A) receptor systems.     

Prostaglandin E2 stimulates cystogenesis through EP4 receptor in IMCD-3 cells

Previously, we demonstrated that prostaglandin E(2) (PGE(2)) induced cAMP and cyst formation through PGE(2) receptor-2 (EP2) activity in human autosomal-dominant polycystic kidney disease (ADPKD) epithelial cells. In this study, we determined the role of EP2 and EP4 receptors in mediating PGE(2) stimulation of cAMP signaling and cystogenesis in mouse renal epithelial cells using the inner medullary collecting duct-3 (IMCD-3) cell line. In contrast to human ADPKD cells, using novel EP2 and EP4 antagonists, we found that IMCD-3 cells expressed functional EP4 but not EP2, which stimulated cAMP formation and led to cyst formation in 3D culture system. The involvement of EP4 receptors in IMCD-3 cells was further supported by the specific effect of EP4 siRNA that inhibited PGE(2)-induced cystogenesis. We also observed different cellular localization of EP2 or EP4 receptors in IMCD-3 transfected cells. Collectively, our results suggest an important role of different expression of EP2 or EP4 receptors in the regulation of cystogenesis.