Inhibition Of Prostanoids Research Articles

Cyclooxygenase-2 inhibition: Vascular inflammation and cardiovascular risk

The inducible isoform of cyclooxygenase-2 (COX-2) plays a role in pathophysiologic processes like inflammation and pain but is also constitutively expressed in tissues such as the kidney or vascular endothelium, where it exerts important physiologic functions. Although much evidence exists that implicates COX-2 in atherosclerosis, its role in this setting remains substantially uncertain. This observation is also confirmed by the results of clinical trials of selective COX-2 inhibitors. Treatment with these drugs, developed with the assumption that they would be as effective as nonselective COX inhibitors but without their gastrointestinal side effects, has been reported to be associated with an increased cardiovascular risk. In this article, we review the pattern of expression of COX-2 in the cellular players of atherothrombosis, its role as a determinant of plaque vulnerability, and the vascular effects on prostanoid inhibition by COX-2 inhibitors.

Nitric oxide blunts the endothelin-mediated pulmonary vasoconstriction in exercising swine.

We have previously shown that vasodilators and vasoconstrictors that are produced by the vascular endothelium, including nitric oxide (NO), prostanoids and endothelin (ET), contribute to the regulation of systemic and pulmonary vascular tone in swine, in particular during treadmill exercise. Since NO and prostanoids can modulate the release of ET, and vice versa, we investigated the integrated endothelial control of pulmonary vascular resistance in exercising swine. Specifically, we tested the hypothesis that increased NO and prostanoid production during exercise limits the vasoconstrictor influence of ET, so that loss of these vasodilators results in exaggerated ET-mediated vasoconstriction during exercise. Fifteen instrumented swine were exercised on a treadmill at 0-5 km h(-1) before and during ET(A)/ET(B) receptor blockade (tezosentan, 3 mg kg(-1) I.V.) in the presence and absence of inhibition of NO synthase (N(omega)-nitro-L-arginine, 20 mg kg(-1) I.V.) and/or cyclo-oxygenase (indometacin, 10 mg kg(-1) I.V.). In the systemic circulation, ET receptor blockade decreased vascular resistance at rest, which waned with increasing exercise intensity. Prior inhibition of either NO or prostanoid production augmented the vasodilator effect of ET receptor blockade, and these effects were additive. In contrast, in the pulmonary bed, ET receptor blockade had no effect under resting conditions, but decreased pulmonary vascular resistance during exercise. Prior inhibition of NO synthase enhanced the pulmonary vasodilator effect of ET receptor blockade, particularly during exercise, whereas inhibition of prostanoids had no effect, even after prior NO synthase inhibition. In conclusion, endogenous endothelin limits pulmonary vasodilatation in response to treadmill exercise. This vasoconstrictor influence is blunted by NO but not by prostanoids.

Relative contribution of vasodilator prostanoids, NO, and KATP channels to human forearm metabolic vasodilation.

Isolated ATP-sensitive K(+) (K(ATP)) channel inhibition with glibenclamide does not alter exercise-induced forearm metabolic vasodilation. Whether forearm metabolic vasodilation would be influenced by K(ATP) channel inhibition in the setting of impaired nitric oxide (NO)- and prostanoid-mediated vasodilation is unknown. Thirty-seven healthy subjects were recruited. Forearm blood flow (FBF) was assessed using venous occlusion plethysmography, and functional hyperemic blood flow (FHBF) was induced by isotonic wrist exercise. Infusion of N(G)-monomethyl-l-arginine (l-NMMA), aspirin, or the combination reduced resting FBF compared with vehicle (P < 0.05). Addition of glibenclamide to l-NMMA, aspirin, or the combination did not further reduce resting FBF. l-NMMA decreased peak FHBF by 26%, and volume was restored after 5 min (P < 0.05). Aspirin reduced peak FHBF by 13%, and volume repaid after 5 min (P < 0.05). Coinfusion of l-NMMA and aspirin reduced peak FHBF by 21% (P < 0.01), and volume was restored after 5 min (P < 0.05). Addition of glibenclamide to l-NMMA and aspirin did not further decrease FHBF. Vascular K(ATP) channel blockade with glibenclamide does not affect resting FBF or FHBF in the setting of NO and vasodilator prostanoid inhibition.

Effect of a single dose aspirin on platelets in humans with multiple risk factors for coronary artery disease

We sought to assess how one tablet of non-enteric coated aspirin (325 mg) affects human platelets in subjects with risk factors for coronary artery disease. Data from 63 individuals with multiple cardiac risk factors were analyzed. Platelets were assessed twice at baseline (pre-aspirin), and after 3–4 h (post-aspirin). We employed 5 μM epinephrine-induced conventional aggregometry, closure time with epinephrine/collagen cartridge by PFA-100® (Dade-Behring), and aspirin response units (ARU) stimulated by propyl gallat with Ultegra® (Accumetrics, San Diego, CA, USA) for measuring platelet function. In addition, the expression of platelet receptors was determined by using the following monoclonal antibodies: anti-CD31, CD41, CD42b, CD51/CD61, CD62p, CD63, CD107a, and CD151. Platelet–leukocyte formation was detected utilizing dual antibodies for a pan-platelet marker CD151, and CD14, a monocyte/macrophage marker. PAC-1 was used to measure fibrinogen–platelet binding. One pill of aspirin significantly decreased platelet-rich plasma (PRP) aggregation (74.18±16.75% vs. 24.92±8.64%; p<0.0001) and resulted in reduction of the aspirin response units (ARU) (662.24±65.65 vs. 451.05±69.31; p<0.0001). There was also prolongation of the closure time (194.4±25.3 vs. 258.63±55.61 s; p<0.0001). High correlation ( r 2=0.73–0.86) between platelet analyzer readings and aggregation was observed. One tablet of aspirin moderately inhibited expression of most surface platelet receptors measured, and such inhibition reached significance ( p<0.05) for PAC-1, CD31, CD41, CD42, CD62p, and CD151. We conclude that a single dose of aspirin affects major platelet receptors, presumably directly or indirectly through the inhibition of prostanoids via platelet cyclooxygenase-1 blockade. The Ultegra® Analyzer with a novel cartridge seems to be reliable in reflecting aspirins' effects on platelets and could be used in the future in clinical practice for monitoring aspirin therapy.

Effects of acetaminophen on constitutive and inducible prostanoid biosynthesis in human blood cells.

1. Acetaminophen, an analgesic and antipyretic drug with weak antiinflammatory properties, has been suggested to act as a tissue-selective inhibitor of prostaglandin H synthases (PGHSs) (e.g. COX-1 and COX-2) through its reducing activity, that is influenced by the different cellular levels of peroxides. 2. We have studied the effects of acetaminophen on inducible and constitutive prostanoid biosynthesis in monocytes and platelets in vitro. To discriminate between the inhibitory effect of the drug on PGHS-isozymes vs PGE-synthases (PGESs), parallel measurements of PGE(2) and thromboxane (TX) B(2) were carried out. Since antioxidant enzymes and cofactors, present in plasma, may affect acetaminophen-dependent inhibition of prostanoids, comparative experiments in whole blood vs isolated monocytes were performed. 3. Acetaminophen inhibited LPS-induced whole blood PGE(2) and TXB(2) production, in a concentration-dependent fashion [IC(50) microM (95% confidence intervals): 44 (27-70) and 94 (79-112), respectively]. Therapeutic plasma concentrations (100 and 300 microM) of the drug more profoundly reduced PGE(2) than TXB(2) (71 +/- 3 vs 54 +/- 4 and 95 +/- 0.8 vs 78 +/- 2%, respectively, mean +/- s.e.mean, n = 6, P < 0.01). 4. Differently, in isolated monocytes stimulated with LPS, both PGE(2) and TXB(2) production was maximally reduced by only 60%. 5 At 100 and 300 microM, the drug caused a similar and incomplete inhibition of platelet PGE(2) and TXB(2) production during whole blood clotting (45 +/- 4 vs 54 +/- 4 and 75 +/- 2 vs 75 +/- 1%, respectively, mean +/- s.e.mean, n = 4). 6 In conclusion, therapeutic concentrations of acetaminophen caused an incomplete inhibition of platelet COX-1 and monocyte COX-2 but in the presence of plasma, the drug almost completely suppressed inducible PGE(2) biosynthesis through its inhibitory effects on both COX-2 and inducible PGES.

Anti-inflammatory activity of a novel selective cyclooxygenase-2 inhibitor, FR140423, on type II collagen-induced arthritis in Lewis rats

The mechanism of action of FR140423 (3-(difluoromethyl)-1-(4-methoxyphenyl)-5-[4-(methylsulfinyl)-phenyl]pyrazole), a novel and selective cyclooxygenase (COX)-2 inhibitor, in rat type II collagen-induced arthritis was investigated and compared with that of indomethacin. We tested the inhibitory effects of FR140423 on paw edema and the formation of arachidonic acid metabolites in inflamed paws immunized with type II collagen. Oral administration of FR140423 showed a dose-dependent anti-inflammatory effect and was two-fold more potent than indomethacin. The increase of prostaglandin (PG) E 2 and thromboxane (TX) B 2 but not leukotriene B 4 in inflamed paws was associated with the development of paw edema. FR140423 and indomethacin dose-dependently suppressed the levels of PGE 2 and TXB 2 in arthritic rat paws. Unlike indomethacin, FR140423 did not induce gastric lesions in arthritic rats. These results suggest that FR140423 shows a potent anti-inflammatory effect mediated by inhibition of prostanoids produced by COX-2 in inflamed tissues immunized with type II collagen, with a greatly improved safety profile compared to indomethacin.

Cyclooxygenase-2 (COX-2) enzyme inhibitors as potential enhancers of tumor radioresponse

Cyclooxygenase-2 (COX-2) is an enzyme induced by a variety of factors including tumor promoters, cytokines, growth factors and hypoxia. It is involved in the metabolic conversion of arachidonic acid to prostanoids, primarily in inflammatory states and tumors. In normal tissues, prostanoids are synthesized by COX-1, and they exert numerous homeostatic physiologic functions. COX-2 overexpression is linked to carcinogenesis, maintenance of progressive tumor growth and facilitation of metastatic spread. COX-2 and its products may act as protectors against cell damage by ionizing radiation. I describe findings showing that inhibition of COX-2 or prostanoids by selective COX-2 inhibitors or commonly used nonsteroidal antiinflammatory drugs (NSAIDs) has antitumor activity and may improve tumor response to radiation without significantly affecting normal tissue radioresponse. COX-2 inhibitors and radiation interact in multiple complex ways, with the enzyme inhibitor directly or indirectly augmenting tumor cell destruction by radiation. COX-2 represents a potential molecular target for improvement of cancer radiotherapy.

Dietary n-3 and n-6 polyunsaturated oils and airway contractility

Recent reports suggest modulation of chronic obstructive pulmonary disease by dietary polyunsaturated fatty acids. In the present study, we re-examined this possibility by using an established animal model of pulmonary sensitisation. Adult guinea pigs were fed diets supplemented (10% w/w) with either olive, canola or safflower oil for 4 weeks before sensitising with ovalbumin and continuing on various diets for a further 6 week period. Neither the contraction following ovalbumin challenge, nor the responses to histamine, carbachol and various eicosanoid mediators – prostaglandin F2α, leukotriene C4, thromboxane mimetic U44619 – of isolated segments of airway tissue were altered (P>0.05, ANOVA) by the dietary lipid treatment. Lipid analysis showed changes in membrane linoleic acid (18:2n-6) and α -linolenic acids (α 18:3n-3) in lung phospholipids consistent with dietary intakes. However, no significant further desaturation/elongation of these dietary precursors was evident. Ovalbumin induced contraction was fully reversed by the lipoxygenase inhibitor esculetin whilst indomethacin resulted in a slight increase possibly due to the inhibition of bronchodilator prostanoids. Results confirm that under the conditions employed airway function was not influenced by the variable dietary intakes of n-3 and n-6 PUFA.

Hypersensitivity to pyrazolones

To the allergologist, hypersensitivity to drugs means immunological drug reactions as classified in the Gell and Coombs system. To others, it may also include non-dose related adverse drug reactions including...

Contribution of vasodilator prostanoids and nitric oxide to resting flow, metabolic vasodilation, and flow-mediated dilation in human coronary circulation.

Endothelial dysfunction is associated with atherosclerosis and may contribute to ischemic syndromes. We assessed the contribution of endothelium-derived nitric oxide (NO) and vasodilator prostanoids to resting blood flow, metabolic vasodilation, and flow reserve in the human coronary circulation. Coronary hemodynamics were assessed before and after inhibition of vasodilator prostanoids and NO with intracoronary aspirin (acetylsalicylic acid [ASA]) and N(G)-monomethyl-L-arginine (L-NMMA), respectively. Angiographically smooth or mildly irregular vessels, with normal adenosine-induced coronary flow reserve, were studied in 25 patients undergoing clinically indicated procedures. Coronary blood velocity was measured by Doppler flow wire, and coronary blood flow (CBF) was calculated. ASA reduced resting conduit vessel diameter by 11% (P = 0.003) and CBF by 27% (P = 0.008) and increased coronary vascular resistance (CVR) by 24% (P<0.0001). ASA attenuated pacing-induced hyperemia by 28% (45.0+/-4.6 versus 32.6+/-3.4 mL/min, P = 0.005) and increased minimum CVR by 39% (2.8+/-0.3 versus 3.9+/-0.5 mm Hg x mL(-1) x min(-1), P = 0.007). L-NMMA reduced resting conduit vessel diameter by 9% (P = 0.05) and CBF by 20% (P = 0.08) and increased CVR by 19% (P = 0.03). L-NMMA attenuated pacing-induced hyperemia by 20% (42.4+/-5.1 versus 34.1+/-3.4 mL/min, P = 0.04) and increased minimum CVR by 33% (2.9+/-0.4 versus 3.8+/-0.5 mm Hg x mL(-1) x min(-1), P = 0.02). ASA (7.7+/-2.3% versus -1.6+/-3.2%, P = 0.06) and L-NMMA (12.1+/-3.9% versus 0.0+/-2.9%, P = 0.02) abolished pacing-induced conduit vessel flow-mediated dilation. Conclusions-Tonic release of vasodilator prostanoids and NO contributes to resting conduit and resistance vessel tone and to peak functional hyperemia and flow-mediated dilation after metabolic stimulation. This underscores the importance of normal endothelial function for metabolic vasodilation and suggests that it may be a key mechanism for preventing myocardial ischemia in coronary artery disease.

Rationale Verwendung nicht-steroidaler antiphlogistischer Analgetika (inklusive selektiver COX-2-Hemmer) in der Praxis

Non-steroidal antiinflammatory drugs NSAIDs exert their pharmacological and side effects by suppressing the activity of the enzyme cyclooxygenase (COX). The identification and molecular- biological characterization of an inducible COX isoform (COX-2) in inflammatory cells led to the hypothesis that a selective inhibition of COX-2 would result in relieve of inflammation and pain without causing the COX-1-dependent side effects. However, all currently available NSAIDs inhibit both COX-1 and COX-2 at therapeutic doses, although they vary in their relative potencies against the two isozymes. Whereas the mechanism-based side effect of NSAIDs (e.g., gastrointestinal and renal toxicity, platelet dysfunctions) are due to a suppression of COX-1-derived prostanoids, an inhibition of prostanoids produced by COX-2 can be ascribed to the antiinflammatory, analgesic and antipyretic effects of NSAIDs. Furthermore, evidence has increased during the last two decades that the pharmacokinetic profil of NSAIDs (i.e., rate of absorption, elimination half-life and oral bioavailability) contributes to either therapeutic effects as well as to the type and incidence of side effects. Thus, the pharmacokinetic behaviour should be considered for the optimal clinical use of these substances. In the present review, the different pharmacokinetics of NSAIDs, their side effects, and perspectives of a therapy with novel specific inhibitors of the COX-2 isozyme are discussed.

Inhibitory prostanoid EP receptors in human non-pregnant myometrium

Prostanoid EP receptor agonists relaxed cloprostenol-stimulated contraction of human non-pregnant myometrium in vitro with pEC 50 values of ( n=4): prostaglandin E 2, 7.8±0.2>1-OH prostaglandin E 1, 7.2±0.3>misoprostol, 6.6±0.1>16,16-dimethyl prostaglandin E 2, 6.3±0.7>butaprost, 5.7±0.3>11-deoxy prostaglandin E 1, 5.5±0.2=AH13205 ((±)- trans-2-[4-(1hydroxyhexyl)phenyl]-5-oxocyclopentaneheptanoic acid), 5.5±0.2. The EP 4 receptor antagonist AH23848B ([1α(z), 2β5α]-(±)-7-[5-[[(1,1′-biphenyl)-4-yl]methoxy]-2-(4-morpholinyl)-3-oxo-cyclopentyl]-4-heptenoic acid) (29 μM) had no effect on concentration–effect curves to the EP receptor agonists. The mixed prostanoid receptor antagonist AH6809 (6-isopropoxy-9-oxaxanthene-2-carboxylic acid) competitively antagonised prostaglandin E 2 with a p A 2 of 5.6±0.2. AH6809 (42 μM) antagonised misoprostol, 11-deoxy prostaglandin E 1, and the prostanoid DP receptor agonist BW245C (5-(6-carboxyhexyl)-1-(3-cyclohexyl-3-hydroxypropyl)hydantoin) with apparent p A 2 values of 5.6±0.3, 5.1±0.9 and 5.9±0.4 ( n=4), respectively, but was ineffective against the IP receptor agonist cicaprost ( n=4). The prostanoid DP receptor antagonist BW A868C (3-benzyl-5-(6-carboxyhexyl)-1-(2-cyclohexyl-2-hydroxyethylamino)hydantoin) (50 nM) had no effect on responses to prostaglandin E 2 or misoprostol. The presence of an AH6809-sensitive, AH23848B- and BW A868C-insensitive mechanism is consistent with the hypothesis that inhibitory EP receptor agonists cause relaxation of human non-pregnant myometrium by an EP 2 receptor-mediated process.

Cerebrospinal fluid prostaglandins after systemic dipyrone intake.

The object of this study was to evaluate the time course of thromboxane B2 and prostaglandin E2 concentrations in cerebrospinal fluid after oral administration of dipyrone (INN, metamizole). A single 1.0 gm oral dose of dipyrone was given to consenting patients undergoing elective diagnostic lumbar puncture 0.5, 1, 1.5, 2, 4, 6, 8, or 12 hours before the tap. For thromboxane B2 a time decrease in cerebrospinal fluid concentration was apparent. In contrast, for prostaglandin E2 cerebrospinal fluid levels no consistent trend was observed. A time-related decrease in cerebrospinal fluid thromboxane B2 level was noted in patients receiving dipyrone. Thirty minutes after dipyrone intake cerebrospinal fluid thromboxane B2 levels already tended to be lower than those seen in patients with neurologic diseases who were not receiving dipyrone. These results are consistent with the hypothesis that dipyrone acts in the central nervous system by inhibition of particular prostanoids.

The endogenous insulin-like growth factor system in radiocontrast nephropathy.

The response of insulin-like growth factor (IGF) I in acute renal failure was evaluated in a model of radiocontrast nephropathy associated with selective necrosis of medullary thick ascending limbs. In brief, rats were administered radiocontrast medium or vehicle injections for controls after combined inhibition of prostanoids and nitric oxide. Twenty-four hours after the insult, tissue mRNAs for IGF-I, the IGF-I receptor, and IGF-binding proteins (IGFBP) 1 and 3 were assayed in cortex, medulla, and liver by solution hybridization-RNase protection assay, and IGFBPs were measured in serum and tissue by Western ligand blotting. Cortical IGF-1 increased, whereas medullary IGF-I mRNA decreased. Renal IGFBPs decreased, whereas IGFBP-1 mRNA increased. The IGF system in the liver was unchanged. We conclude that general changes in renal IGFBPs in this experimental model of acute renal failure might increase the level of cortical IGF-I in a way that could modulate medullary recovery.

The Effect of Dexamethasone on CRH and Prostanoid Production from Human Term Placenta

The human placenta at term produces large quantities of corticotropin releasing hormone (CRH) and prostanoids. These hormones play an important role in the maintenance of pregnancy, and the initiation and progress of labor; yet little is known of factors affecting their regulation and the interrelationship of CRH and prostanoid production. In these studies we have investigated the effect of dexamethasone on the production of CRH and prostanoids from fresh human term placental tissues. The basal release of prostaglandin E 2 (PGE 2), prostaglandin F 2α (PGF 2α), thromboxane B 2 (TxB 2) and 6-keto-prostaglandin F 1α (6-keto-PGF 1α) from human term placental explants increased from the fifth hour in culture, while the release of 13,14-dihydro-15-keto-PGE 2α (PGFM) was not significantly changed during this period. The addition of dexamethasone (10 −8 M) to the perifusing medium resulted in a rapid and dramatic inhibition of PGE 2, PGF 2α, PGFM, TxB 2 and 6-keto-PGF 1α release. On the other hand, CRH release was not significantly changed throughout the seven hours of incubation with dexamethasone. These data demonstrate that glucocorticoids at physiologic concentrations can inhibit human term placental prostanoid production, and thus glucocorticoid production may play an important role in the physiological regulation of placental prostanoid production in the human placenta. However, dexamethasone did not alter CRH release, demonstrating that the inhibition of placental prostanoids by dexamethasone is not a CRH mediated event.

Characterization of the prostanoid receptor(s) on human blood monocytes at which prostaglandin E2 inhibits lipopolysaccharide-induced tumour necrosis factor-alpha generation.

1. The prostanoid receptor(s) that mediates inhibition of bacterial lipopolysaccharide (LPS)-induced tumour necrosis factor-alpha (TNF-alpha) generation from human peripheral blood monocytes was classified by use of naturally occurring and synthetic prostanoid agonists and antagonists. 2. In human monocytes that were adherent to plastic, neither prostaglandin D2 (PGD2), prostaglandin E2 (PGE2), prostaglandin F(2 alpha) (PGF(2 alpha)) nor the stable prostacyclin and thromboxane mimetics, cicaprost and U-46619, respectively, promoted the elaboration of TNF alpha-like immunoreactivity, as assessed with a specific ELISA, indicating the absence of excitatory prostanoid receptors on these cells. 3. Exposure of human monocytes to LPS (3 ng ml-1, approximately EC84) resulted in a time-dependent elaboration to TNF alpha which was suppressed in cells pretreated with prostaglandin E1 (PGe1), PGE2 and cicaprost. This effect was concentration-dependent with mean pIC50 values of 7.14, 7.34 and 8.00 for PGE1, PGE2 and cicaprost, respectively. PGD2, PGF(2 alpha) and U-46619 failed to inhibit the generation of TNF alpha at concentrations up to 10 microM. 4. With respect to PGE2, the EP-receptor agonists, 16,16-dimethyl PGE2 (non-selective), misoprostol (EP2/EP3-selective), 11-deoxy PGE1 (EP2-selective) and butaprost (EP2-selective) were essentially full agonists as inhibitors of LPS-induced TNF alpha generation with mean pIC50 values of 6.21, 6.02, 5.67 and 5.59, respectively. In contrast to the results obtained with butaprost and 11-deoxy PGE1, another EP2-selective agonist, AH 13205, inhibited TNF alpha generation by only 21% at the highest concentration (10 microM) examined. EP-receptor agonists which have selectively for the EP1- (17-phenyl-omega-trinor PGE2) and EP3-receptor (MB 28,767, sulprostone) were inactive or only weakly active as inhibitors of TNF alpha generation. 5. Pretreatment of human monocytes with the TP/EP4-receptor antagonist, AH 23848B, at 10, 30 and 100 microM suppressed LPS-induced TNF alpha generation by 10%, 28% and 77%, respectively, but failed to shift significantly the location of the PGE2 concentration-response curves. 6. Given that AH 13205 was a poor inhibitor of TNF alpha generation, studies were performed to determine if it was a partial agonist and whether it could antagonize the inhibitory effect of PGE2. Pretreatment of human monocytes with 10 and 30 microM AH 13205 inhibited the generation of TNF alpha by 31% and 53%, respectively, but failed to shift significantly the location of the PGE2 concentration-response curves at either concentration examined. 7. Since PGD2 and 17-phenyl-omega-trinor PGE2 (EP1-agonist) did not suppress TNF alpha generation, the EP1/EP2/DP-receptor antagonist, AH 6809, was employed to assess if EP2-receptors mediated the inhibitory effect of PGE2. Pretreatment of human monocytes with 10 microM AH 6809 did not affect LPS-induced TNF alpha generation but produced a parallel 3.5 fold rightwards shift of the PGE2 concentration-response curve. 8. Collectively, these data suggest that human peripheral blood monocytes express at least two distinct populations of inhibitory prostanoid receptors that mediate inhibition of LPS-induced TNF alpha generation. One of these probably represents i.p. receptors based upon the selectivity of cicaprost for this subtype. The other population has the pharmacology of EP-receptors, but the rank of potency for a range of synthetic EP-receptor agonists was inconsistent with an interaction with any of the currently defined subtypes. Given the pharmacological behaviour of butaprost, AH 6809 and AH 23848B in these cells, we propose that multiple (EP2- and/or EP-4- and/or i.p.) or novel EP-receptors mediate the inhibitory effect of PGE2 on TNF alpha generation.

In vitro responses of equine small airways and lung parenchyma

In vitro responses of equine small peripheral airways (SA) and lung parenchyma (LP) were studied. We examined their contractile and relaxant responses and investigated effects of histamine, and endogenous prostanoids as these mediators may play a role in development of recurrent airway obstruction in horses (heaves). SA and LP electrical field stimulation (EFS) induced nearly maximal and partial frequency-dependent contractions, respectively. These contractions were virtually abolished in SA but only partially inhibited in LP by atropine (ATR) and tetrodotoxin (TTX). Methacholine (MCh) contracted SA with a 5-fold higher potency and greater maximal tension than LP. In SA but not in LP, a large augmentation of EFS responses at 1–4 Hz was produced by both meclofenamate, a cyclooxygenase blocker and 3 μM histamine. We conclude that: (1) excitatory input from cholinergic nerves largely determines SA tone, but has minor effect in LP; (2) in SA endogenous inhibitory prostanoids modulate contractile response to nerve stimulation; and (3) inhibition of cyclooxygenase and histamine greatly potentiate responses to nerve stimulation in SA. These data are consistent with the hypothesis that, in horses with heaves, histamine release and an altered prostanoid profile contribute to cholinergically mediated SA obstruction.

Beneficial Effect of ETA Receptor Blockade in a Rat Model of Radiocontrast-Induced Nephropathy

Endothelin has been implicated in the pathogenesis of acute renal failure associated with radiocontrast media. The current study was designed to determine the effect of endothelin receptor blockade in a model of radiocontrast-induced nephropathy. Inhibition of prostanoids and nitric oxide with indomethacin and L-nitroarginine methyl ester (L-NAME) predisposes rats to the nephrotoxic effects of radiocontrast media and, therefore, has been proposed as a clinically relevant model. Separate groups of conscious rats were given the ETA receptor antagonist, A-127722 (3, 10, or 30 mg/kg), or water (I mL/kg) by oral gavage. All rats were then given indomethacin (10 mg/kg), L-NAME (10 mg/kg), and the contrast agent, diatrizoate (6 mL/kg), by intravenous injection at 15-min intervals. Urine was collected for the subsequent 24 h by placing rats in metabolism cages. When indomethacin, L-NAME, and diatrizoate were administered without A-127722, rats displayed typical signs of renal failure; protein excretion was increased from a baseline of 13±2 to 33 ± 8 mg/day (p < 0.05) and plasma creatinine increased from 0.52 ± 0.01 to 0.62 ± 0.04 mg/dL (p < 0.05). ETA receptor blockade prevented the rise in protein excretion and plasma creatinine in a dose-dependent manner. In separate series of clearance experiments, A-127722 completely inhibited the renal effects of exogenous ET-1. These results suggest that endothelin plays a role in the hemodynamic events in this model and that ETA receptor antagonists should be investigated as potential therapeutic agents for radiocontrast-induced nephropathy.

Origin and modulation of ACh release from rat airway cholinergic nerves

The release of acetylcholine (ACh) from airway parasympathetic nerves was studied in rat trachea. We established stimulus parameters, examined the role of extracellular Ca2+, and investigated the origin of the released ACh by use of vesamicol, an inhibitor of ACh uptake in synaptic vesicles. The role of muscarinic autoreceptors and prostanoids on ACh release was also studied. Tracheal rings were incubated in Krebs-Henseleit solution containing neostigmine and guanethidine with or without atropine. ACh release was measured by high-performance liquid chromatography with electrochemical detection. ACh release was dependent on frequency (0.5-16 Hz), voltage (10-25 V), and pulse duration (0.5-4 ms). At 4 Hz, one-fifth of electrical field stimulation-induced ACh release was extracellular Ca2+ independent and vesamicol resistant, indicating its nonvesicular origin. Three-fifths were Ca2+ dependent and vesamicol sensitive, indicating that it was newly synthesized, and one-fifth was Ca2+ dependent but vesamicol resistant, indicating its origin from prestored vesicles. At 16 Hz, two-fifths were nonvesicular and three-fifths were newly synthesized. Blockade of the muscarinic autoreceptor by atropine potentiated the release of ACh four- to fivefold. Neither of the cyclooxygenase inhibitors indomethacin or meclofenamate nor exogenous prostaglandin E2 affected ACh release, indicating that inhibitory prostanoids do not modulate ACh release.

Release and actions of inhibitory prostaglandins from canine tracheal epithelium

This study evaluated the sources and actions of inhibitory prostanoids on canine tracheal smooth muscle to determine if these accounted for epithelium derived relaxing factor activity. Concentration-response curves of canine tracheal smooth muscle were generated to carbachol in the presence and absence of the epithelium and (or) indomethacin, a cyclooxygenase inhibitor. Removal of the epithelium or addition of indomethacin (10(-5) M) in the presence of the epithelium shifted the curve significantly leftward compared with epithelial-intact tissue. Furthermore, addition of indomethacin to epithelial-denuded tissue produced the greatest shift in the curve. Removal of the epithelium increased contractility in response to electrical-field stimulation at intermediate frequencies compared with epithelium-intact tissues. The addition of indomethacin to epithelium-intact tissue also increased the contractile responses. Removal of the epithelium in the presence of indomethacin further increased responses. Radioimmunoassay of muscle bath fluid indicated that the inhibitory prostanoids prostaglandin I2 (PGI2) and prostaglandin E2 (PGE2) were released. PGI2 was released from the epithelium as well as from a nonepithelial source. PGE2 was released from the epithelium in response to electrical-field stimulation. The release of PGE2 was greatly reduced by the addition of indomethacin (10(-5) M), but not by the addition of omega-conotoxin (GVIA), an N-type Ca2+ channel antagonist, nor by the addition of tetrodotoxin, a Na+ channel blocker. Both toxins abolished contractions to electrical-field stimulation. We conclude that the inhibitory prostanoids PGI2 and PGE2 are released, along with a nonprostanoid factor from epithelium, and modulate airway smooth muscle contractility to stimulation of cholinergic nerves and muscarinic agonists. PGE2 is released from epithelium by electrical-field stimulation independent of nerve function.