Pharmacological study of the contractile activity of leukotriene C4 and D4 on isolated human airway smooth muscle

The efficacy of montelukast and airway mast cell profiles in patients with cough variant asthma

BACKGROUND

Cough variant asthma (CVA) is characterized by chronic cough without apparent wheezing; its pathophysiology is considered to be similar to that of classic asthma.

OBJECTIVE

The clinical effects of montelukast, a cysteinyl-leukotriene receptor antagonist, on cough variant asthma were assessed, and the activation profile of airway mast cells was examined.

METHODS

Montelukast (10 mg/day) was given orally to 36 CVA patients (25 women and 11 men; median age, 37.5 years). Before treatment, the patients' bronchial mucosa underwent a biopsy with a fiberoptic bronchoscope. The biopsy specimens were double stained with anti-CD63 antibody and anti-human tryptase antibody.

RESULTS

After 2 weeks of montelukast treatment, cough symptoms improved in 22 patients (the effective group) but did not improve in 14 patients (the ineffective group); in the ineffective group, the symptoms disappeared 2 weeks after they were switched to fluticasone propionate (400 microg/day) inhalation therapy. In the effective group, the time interval from the onset of symptoms to the initiation of treatment was significantly shorter than in the ineffective group. The bronchial mucosa biopsy specimens showed that the proportion of CD63-positive cells in tryptase-positive mast cells was significantly higher in the effective group than in the ineffective group; although the total numbers of mast cells were not different between the two groups.

CONCLUSION

There is a subgroup of CVA patients in whom leukotrienes are closely involved in the pathogenesis of their chronic cough; activation of airway mast cells may be an essential feature in these patients.

Treatment of asthma with antileukotrienes: first line or last resort therapy?

Twenty five years after the structure elucidation of slow reacting substance of anaphylaxis, antileukotrienes are established as a new therapeutic modality in asthma. The chapter reviews the biochemistry and pharmacology of leukotrienes and antileukotrienes with particular focus on the different usage of antileukotrienes for treatment of asthma and rhinitis in Europe and the US. Further research needs and new areas for leukotriene involvement in respiratory diseases are also discussed.

Bronchoconstriction provoked by exercise in a high-particulate-matter environment is attenuated by montelukast

Airborne ultrafine and fine particulate matter (PM1 from fossil-fueled internal combustion engines may cause abnormal airway narrowing. Because of high PM1 exposure from ice resurfacing machines, the ice-rink athlete is especially vulnerable to PM1 toxicity. The purpose of this study was to evaluate protection by a single dose of montelukast in college ice hockey players following PM1 exposure exercise. Nine male ice hockey players (age 19.3+/-1.22 yr) performed 4 randomized, double-blinded, high-intensity, 6-min cycle ergometer trials in low [PM1] (2260+/-500 particles/cm3) and high [PM1] (348,600+/-121,600 particles/cm3) after placebo or montelukast. Pre- and postspirometry showed similar peak FEV1 (forced expiratory volume in 1 s) falls between placebo and montelukast after low [PM1] trials (14.5+/-18.06 vs. 9.5+/-11.75% of baseline, respectively). Peak FEV1 falls after high [PM1] trials were greater for placebo than for montelukast (17.3+/-9.79% vs. 1.7+/-5.77% of baseline; p<.0001). High [PM1] FEV1 fall after exercise following montelukast ingestion was less than after exercise following placebo ingestion under high and low [PM1] conditions and after exercise following montelukast ingestion under low [PM1] conditions at 5, 10, and 15 min postchallenge (p<.004, .0006, .009, respectively). Montelukast provided greater protection against bronchoconstriction after exercise during high [PM1] than low [PM1] exposure (approximately 90% vs. approximately 35%), suggesting that bronchoconstriction from PM1 exposure is predominately leukotriene mediated. The precise mechanism of airborne PM1-induced leukotriene-mediated airway narrowing remains unclear.

Leukotriene E(4)-induced persistent eosinophilia and airway obstruction are reversed by zafirlukast in patients with asthma

BACKGROUND

We have shown that inhalation of leukotriene (LT) E 4 contributes to specific recruitment of eosinophils to the airway mucosa in patients with asthma at the time of maximal decrease in airway-specific conductance.

OBJECTIVE

We examined the ability of the cysteinyl LT 1 receptor antagonist, zafirlukast, to improve or prevent LT-mediated eosinophilia and airway obstruction in asthma.

METHODS

Bronchial biopsies were taken and pulmonary function was measured before and 4 to 6 hours after the dose of inhaled LTE 4 causing a > or =15% fall in FEV 1 at baseline both at week 0 and after 6-week randomly assigned treatment with a high dose of zafirlukast, 80 mg twice daily.

RESULTS

Leukotriene E 4 inhalation at week 0 doubled the number of eosinophils in the airway mucosa in 21 of 25 patients with mild asthma, increased the numbers of neutrophils and lymphocytes, and decreased FEV 1 (-17%). Zafirlukast reduced both airway eosinophilia and obstruction in FEV 1 , whereas with a double-blind placebo treatment, the effect of LTE 4 on both parameters persisted for 6 weeks. On repeat LTE 4 inhalation challenge after 6 weeks, zafirlukast treatment prevented further airway eosinophilia and decrease in FEV 1 seen in the placebo group.

CONCLUSION

Persistent LTE 4 -induced airway eosinophilia may form the basis of an amplification mechanism for further eosinophil recruitment. Zafirlukast prevents LTE 4 -induced eosinophilic airway inflammation in mild asthma.

International Union of Pharmacology XXXVII. Nomenclature for leukotriene and lipoxin receptors

The leukotrienes and lipoxins are biologically active metabolites derived from arachidonic acid. Their diverse and potent actions are associated with specific receptors. Recent molecular techniques have established the nucleotide and amino acid sequences and confirmed the evidence that suggested the existence of different G-protein-coupled receptors for these lipid mediators. The nomenclature for these receptors has now been established for the leukotrienes. BLT receptors are activated by leukotriene B(4) and related hydroxyacids and this class of receptors can be subdivided into BLT(1) and BLT(2). The cysteinyl-leukotrienes (LT) activate another group called CysLT receptors, which are referred to as CysLT(1) and CysLT(2). A provisional nomenclature for the lipoxin receptor has also been proposed. LXA(4) and LXB(4) activate the ALX receptor and LXB(4) may also activate another putative receptor. However this latter receptor has not been cloned. The aim of this review is to provide the molecular evidence as well as the properties and significance of the leukotriene and lipoxin receptors, which has lead to the present nomenclature.

The potential role of tocopherol in asthma and allergies: modification of the leukotriene pathway

Metabolism of arachidonic acid via the 5-lipoxygenase (5-LO) pathway leads to the formation of hydroperoxyeicosatetraenoic acids (HPETEs) and leukotriene (LT) A4. This unstable allylic epoxide can be further converted by secondary enzymes into LTB(4) and cysteinyl LTs. LTs represent a family of potent biologically active compounds synthesised by specific cell types and by transcellular biosynthetic mechanisms. Cysteinyl LTs are involved in the pathogenesis of asthma, and recent data indicate that individuals with asthma may have enhanced basal excretion of urinary LTE4 compared with normal individuals. Tocopherol (vitamin E) and tocopherol acetate strongly inhibit potato 5-LO in an irreversible and noncompetitive way, and, by affecting the redox state of cells possessing 5-LO, they may influence the production of biologically active LTs. It has been reported that normal plasma levels of tocopherol may enhance the lipoxygenation of arachidonic acid, whereas higher tocopherol levels exert a suppressive effect that is consistent with its role as a hydroperoxide scavenger. Receptor-mediated activation of neutrophils in individuals with asthma results in the synthesis of LTs. This activation is inhibited by tocopherol in a concentration-dependent manner. Additional controlled studies are needed to assess the effect of tocopherol on leukotriene production in asthmatic individuals. The results of these studies may be useful in developing new therapeutic approaches in asthmatic/allergic patients.

Thrombin-stimulated DNA synthesis in human cultured airway smooth muscle occurs independently of products of cyclo-oxygenase or 5-lipoxygenase

Arachidonic acid (AA) liberation and metabolism via cyclo-oxygenase or lipoxygenases may be an important regulatory pathway for mitogenic signalling in human cultured airway smooth muscle (ASM) cells. In cytokine-treated cells, thrombin markedly enhances production of the anti-mitogenic arachidonic acid metabolite, PGE(2). In this study, in the absence of cytokines, we examined the role of endogenous AA metabolism in thrombin-stimulated ASM DNA synthesis. Selective inhibitors of cyclo-oxygenase of 5-lipoxygenase metabolism had no significant effect on 0.3 U/ml thrombin-stimulated DNA synthesis. However, the non-selective, redox-active lipoxygenase inhibitors NDGA and BWA4C inhibited thrombin-stimulated DNA synthesis. Under basal conditions, and following stimulation by thrombin, the levels of the AA metabolites PGE(2), TxA(2), and LTC(4), remained below assay detection limits. Exogenous addition of AA, LTD(4), or 5-, 12-, and 15-HETE and HpETE metabolites had no consistent or substantial stimulatory effect on either basal or thrombin-stimulated DNA synthesis. These data suggest that the non-selective lipoxygenase inhibitors influence DNA synthesis via effects unrelated to lipoxygenase inhibition. The lack of detection of AA metabolites, the lack of influence of selective antagonists/inhibitors of the AA pathway, and the failure of selected AA metabolites to either enhance or directly stimulate DNA synthesis suggest that in the absence of cytokines, cyclo-oxygenase and lipoxygenase metabolism has little role in signalling of human ASM DNA synthesis by thrombin.

The role of leukotrienes in the regulation of tone and responsiveness in isolated human airways

Cysteinyl-leukotrienes and histamine are the major determinants of inherent tone in isolated human bronchi, which is mainly the result of a balance of continual production and release of contractile mediator, in particular cysteinyl-leukotrienes and to a lesser extent histamine, and on the other side bronchodilating prostanoids. Cysteinyl-leukotrienes are also powerful constrictors of isolated human airways through direct interaction with Cys-LT1 receptors on airway smooth muscle, and with a potency 1,000-fold higher than histamine. On stimulation inflammatory cells such as eosinophils and mst cells produce and release significantly increased amounts of leukotrienes leading to smooth muscle contration in vitro. In isolated human airways, leukotrienes are the most important mediators of allergen and adenosine-induced contractile responses. The induction of allergen responses in passively sensitized airways is not only related to an increased release of leukotrienes and histamines, but also to an enhanced responsiveness of the airway smooth muscle, particularly to LTC4. Studies in isolated human airways in vitro have demonstrated that understanding the regulation of human airway tone and airway reactivity are closely linked to the understanding of baseline and stimulated production of and smooth muscle responsiveness to leukotrienes in vitro and in vivo.

Asthma therapy with agents preventing leukotriene synthesis or action

Elucidation of the biochemistry of leukotriene production and the pharmacology of its actions has led to the development of a number of therapeutic agents shown to be of value in the treatment of asthma. These agents either prevent the synthesis of the leukotrienes, by preventing the action of the 5-lipoxygenase-activating protein or the catalytic action of the 5-lipoxygenase, or by inhibiting the action of leukotrienes at the CysLT1 receptor. Numerous clinical trials in exercise-induced asthma, allergen-induced asthma, aspirin-induced asthma, and spontaneously occurring asthmatic episodes have indicated that these agents are safe and effective asthma treatments.

The role of cysteinyl leukotrienes in the pathogenesis of asthma: clinical study of leukotriene antagonist pranlukast for 1 year in moderate and severe asthma

Clinical studies have shown that pranlukast (Ono Pharmaceutical Co., Osaka, Japan) is effective for mild and moderate asthma. However, it is not well known that pranlukast is also effective on moderate and severe persistent asthma in the long term. We studied the effect of pranlukast on moderate and severe asthmatics by evaluating the change of peak expiratory flow (PEF) and therapeutic scores for 1 year before and during pranlukast therapy. We gave pranlukast 225 mg twice daily orally to 25 patients who were receiving more than 400 micrograms/day beclomethasone inhalation and beta 2 stimulant inhalation with or without oral corticosteroid. Pranlukast increased PEF more than 10 L/min in 14 patients in the first 4 weeks. In these 14 patients, 10 patients continued to monitor PEF and kept asthma diaries for 1 year. We compared the data for 1 year before and during the pranlukast therapy. During the pranlukast therapy, PEF significantly increased, puffs of beta 2 stimulant inhalation significantly decreased. The incidence of oral corticosteroid rescue therapy reduced, and the mean daily dose of oral corticosteroid decreased; however, they were not statistically significant. During treatment with pranlukast, no side effect was observed. From these results, we suggest that pranlukast is effective for more than half of the moderate and severe persistent asthmatics, and that the effectiveness continues for more than 1 year.

Contraction of human airways by oxidative stress protection by N-acetylcysteine

We examined the in vitro effects of tert-butylhydroperoxide (tBu-OOH) in human bronchial muscle. tert-Butylhydroperoxide produced concentration-dependent contractions of bronchial rings (maximum effect was 56.5 +/- 9.6% of contraction by 1 mM acetylcholine; effective concentration 50% was approximately 100 microM). tert-Butylhydroperoxide (0.5 mM)-induced contraction was enhanced by epithelial removal but abolished by indomethacin (cyclooxygenase inhibitor) and zileuton (lipoxygenase inhibitor). tert-Butylhydroperoxide produced a transient rise in intracellular calcium in human cultured airway smooth muscle cells (HCASMC). The bronchial reactivity to acetylcholine and histamine was not altered by tBu-OOH. In HCASMC, tBu-OOH (0.5 mM, 30 min) increased malondialdehyde levels (MDA; from 7.80 +/- 0.83 to 26.82 +/- 1.49 nmol mg(-1) protein), accompanied by a decrease of reduced glutathione (GSH; from 16.7 +/- 2.6 to 6.9 +/- 1.9 nmol mg(-1) protein) and an increase of oxidized glutathione (from 0.09 +/- 0.03 to 0.18 +/- 0.03 nmol mg(-1) protein). N-acetylcysteine (0.3 mM) inhibited by approximately 60% the bronchial contraction resulting from tBu-OOH (0.5 mM) and protected cultured cells exposed to tBu-OOH (MDA was lowered to 19.51 +/- 1.19 nmol mg(-1) protein, and GSH content was replenished). In summary, tBu-OOH caused contraction of human bronchial muscle mediated by release of cyclo-oxygenase and lipoxygenase products without producing airways hyperreactivity. N-acetylcysteine decreases tBu-OOH-induced contraction and protects human cultured airway smooth muscle cells exposed to tBu-OOH.

Asthma and leukotrienes: antileukotrienes as novel anti-asthmatic drugs

Antileukotriene drugs inhibit the formation or action of leukotrienes, which are potent lipid mediators generated from arachidonic acid in lung tissue and inflammatory cells. The leukotrienes were discovered in basic studies of arachidonic acid metabolism in leucocytes 20 years ago and were found to display a number of biological activities which may contribute to airway obstruction. Clinical studies with antileukotriene drugs have indeed demonstrated that leukotrienes are significant mediators of airway obstruction evoked by many common trigger factors in asthma. Moreover, treatment trials have established that this new class of drugs has beneficial anti-asthmatic properties, and several antileukotrienes have recently been introduced as new therapy of asthma. This communication presents an overview of the biosynthesis of leukotrienes, their biological effects and clinical effects of antileukotrienes in the treatment of asthama.

Leukotrienes as mediators of airway obstruction

The cysteinyl leukotrienes are potent mediators of airway narrowing derived from the lipoxygenation of arachidonic acid and the adduction of glutathione to this eicosanoid backbone. In lower animals and humans, the cysteinyl leukotrienes are among the most potent airway contractile substances ever identified. Furthermore, these moieties can be recovered from the urine during induced or spontaneous asthma attacks. Most important, inhibition of the synthesis of the leukotrienes or prevention of their action at the CysLT1 receptor is associated with an improvement in the airway dysfunction that occurs in both induced and spontaneous asthma. These data indicate that the cysteinyl leukotrienes have a clinically significant role in the airway obstruction that characterizes asthma.

Agonist and antagonist activities of the leukotriene analogue BAY u9773 in guinea pig lung parenchyma

BAY u9773(6(R)-(4'-carboxyphenylthio)-5(S)-hydroxy-7(E),9(E),11( Z),14(Z)-eicosatetraenoic acid) is a leukotriene E4 analogue used to define 'atypical' receptors for cysteinyl-leukotrienes. The aims of this study were first to characterise the intrinsic properties of BAY u9773 in guinea-pig lung parenchyma in vitro and second to study the influence of BAY u9773 on the concentration-response relation for leukotriene D4 in the same preparation. BAY u9773 in itself caused a concentration-dependent contraction, which was not inhibited by the cyclooxygenase inhibitor indomethacin nor by the 5-lipoxygenase inhibitor zileuton (N-(1-benzo-(12)-thien-2-ylethyl)-N-hydroxyurea). The CysLT1 receptor antagonist ICI 198,615 [(1-((2-methoxy-4-(((phenylsulfonyl)amino) carbonyl)phenyl)methyl)-1H-indazol-6-yl)carbamic acid cyclopentyl ester] alone blocked the contractile response to BAY u9773 1 microM, whereas a combination of the TP receptor antagonist BAY u3405 ((3R)-3-(4-fluorophenylsulfonamido)-1,2,3,4-tetrahydro-9-carbaz olepropanoic acid) and ICI 198,615 was required to block the contraction induced by BAY u9773 10 microM. Together the findings suggest that BAY u9773 acted as a CysLT1 receptor agonist and in the higher concentration also as a TP receptor agonist. The CysLT1 receptor antagonist ICI 198,615 partly inhibited the contractile response to leukotriene D4. Pretreatment with BAY u9773 or leukotriene D4, caused concentration-dependent rightward displacement of the concentration-response curve for leukotriene D4. The inhibition by BAY u9773 was partial, and not greater than that produced by ICI 198,615. Combination of BAY u9773 and ICI 198,615 did not produce additive inhibition, suggesting that the major part of the leukotriene D4 induced contraction in guinea pig lung parenchyma is mediated by a CysLT receptor with properties distinct from those of previously described CysLT1 and CysLT2 receptors.

Leukotrienes as a target in asthma therapy

Asthma is a chronic inflammatory condition characterised by bronchial hyper-responsiveness and reversible airways obstruction. Research has demonstrated that these effects are mediated by a wide range of compounds. In the last decade leukotrienes have been identified as products of arachidonic acid metabolism. Their effects mimic the pathological changes seen in asthma both in vitro and in vivo. Further research has demonstrated increased production of leukotrienes both during episodes of asthma and in patients with stable asthma. The demonstration that leukotrienes have proinflammatory biological properties relevant to the pathogenesis of asthma has stimulated the development of many potential therapeutic compounds to block these actions. Early studies in laboratory-induced asthma in human volunteers have shown the efficacy of some of these compounds. They have been shown to attenuate the bronchoconstriction caused by allergen challenge, exercise, aspirin and exposure to cold air. Most encouraging of all have been recent placebo-controlled studies in clinical asthma where significant improvements in terms of spirometry, symptoms and beta 2-agonist use have been demonstrated. Leukotriene receptor antagonists and synthesis inhibitors are the first mediator antagonists to have been shown to be effective in treating clinical asthma and as such represent one of the most interesting new classes of antiasthma drugs in development at present.

Influence of epithelium on the inhibition of melittin-induced contraction of guinea-pig isolated trachea by the potassium channel opener NIP-121

1. We have investigated the effect of the potassium channel opener, NIP-121, on contraction elicited by melittin (a phospholipase A2 activator) in epithelium-intact and epithelium-denuded trachea isolated from guinea-pigs. The effects of NIP-121 were compared with those of isoprenaline, aminophylline and hydrocortisone. 2. In the presence of the cyclo-oxygenase inhibitor, indomethacin (5 microM), melittin (3 micrograms ml-1) caused time-dependent contraction. The melittin-induced contractile response was significantly augmented by removal of the epithelium and was concentration-dependently and completely inhibited by the phospholipase A2 (PLA2) inhibitor, p-bromophenacyl bromide (BPB 10-100 microM), and the lipoxygenase inhibitor, phenidone (10-300 microM). Similar inhibition of the melittin response by BPB (10 microM) and phenidone (10 microM) was observed in the epithelium-denuded trachea. 3. Concentration-dependent inhibition of the melittin response was induced by preincubation with NIP-121 (0.03 and 0.1 microM), isoprenaline (0.001 and 0.01 microM), aminophylline (30 and 100 microM) and hydrocortisone (100 and 300 microM). The effect of NIP-121 was abolished by glibenclamide (1 microM). 4. The inhibitory effect of NIP-121 on the melittin response was greatly reduced by removing the epithelium while that of the isoprenaline, aminophylline or hydrocortisone was not changed. 5. The inhibition of the melittin response by these drugs was similar to their inhibition of the contraction elicited by a low concentration (3 nM) of leukotriene D4 (LTD4) in the epithelium-intact trachea. Inhibition of the LTD4 response by NIP-121 was not observed in the epithelium-denuded trachea. However, higher concentrations of NIP-121 (0.3 and 1 microM) did inhibit LTD4-induced contractions of epithelium-denuded trachea.6. These findings suggest that melittin causes epithelium-dependent contraction of the guinea-pig isolated trachea which is mediated by products of lipoxygenase activity. NIP-121 may inhibit the melittin response by activating glibenclamide-sensitive potassium channels, which appear to be epithelium-dependent (an indirect effect of NIP-121 apart from its direct effect on the airway smooth muscle) while isoprenaline, aminophylline and hydrocortisone act directly to relax the trachealis smooth muscle.

Effect of a new leukotriene receptor antagonist, ONO-1078, on human bronchial smooth muscle in vitro

Peptide leukotrienes (LT) have been postulated to play a major role in the etiology of bronchial asthma. The present study investigated the effect of a new peptide LT receptor antagonist, ONO-1078, on isolated human bronchial smooth muscle in vitro. Helical strips of bronchi were suspended in the organ baths filled with 37 degrees C Krebs solution and mechanical responses were recorded isometrically. ONO-1078 produced dose-dependent relaxations, which suggested that the spontaneous basal tone was in part mediated by LT. ONO-1078 caused dose-dependent relaxations of the tissues which were precontracted with LTC4 or LTD4 (3 x 10(-8) M). Pretreatment of bronchi with ONO-1078 (10(-8) M, 10(-7) M) significantly inhibited dose-dependent contractions induced by LTC4 and LTD4. ONO-1078 (10(-6) M) also significantly reduced the antigen-induced contractions in bronchi passively sensitized with atopic serum from mite-allergic patients. Moreover the combination of an H1-receptor antagonist, diphenhydramine (10(-5) M), and ONO-1078 (10(-6) M) completely abolished the antigen-induced contractions. The present findings demonstrate that ONO-1078 is a potent antagonist of exogenous and endogenous LT in the human airway. The selective LT antagonist such as ONO-1078 may be valuable in the therapy of allergic asthma.

Role of leukotrienes in airway hyperresponsiveness in guinea-pigs

1. Repeated aerosolization of leukotriene C4 (LTC4) to guinea-pigs produced leftward shift in their pulmonary resistance (RL) dose-response curves to inhaled acetylcholine (ACh) without increasing the maximum responses. 2. Repeated LTC4 aerosolization did not increase airway eosinophils. 3. The 5-lipoxygenase-activating protein (FLAP) inhibitor, MK-886, prevented the leftward shift in RL dose-response curves to ACh following repeated antigen challenge in guinea-pigs. 4. MK-886 did not inhibit the increased maximal RL produced by repeated antigen challenge, nor inhibit the airway eosinophilia induced by repeated antigen challenge. 5. Our findings suggest that leukotrienes may account for the leftward shift in pulmonary resistance responses caused by antigen but do not cause the airway eosinophilia nor enhanced maximum broncho-constrictor response to antigen.

Characterization of the leukotriene D4 receptor in dimethylsulphoxide-differentiated U937 cells: comparison with the leukotriene D4 receptor in human lung and guinea-pig lung

The leukotriene D4 receptor has been fully characterized by radioligand binding in membrane preparations from dimethyl sulphoxide-differentiated U937 cells, a human monocyte leukemia cell line, and, in parallel experiments, compared with leukotriene D4 receptor found in human lung and guinea-pig lung preparations. [3H]Leukotriene D4 specific binding in differentiated U937 cell membranes is of high affinity (KD = 0.35 nM), saturable (Bmax = 287 fmol/mg protein), with differentiation resulting in a 3-5-fold increase in the number of detectable binding sites. [3H]Leukotriene D4-specific binding in differentiated U937 cell membranes displays several features of G-protein-coupled receptors, being inhibited by GTP analogues and sodium ions, but increased by divalent cations. These characteristics are shared with [3H]leukotriene D4-specific binding in human and guinea-pig lung preparations. However, differences between these leukotriene D4 receptor types were observed. [3H]Leukotriene D4 equilibrium binding to differentiated U937 cell membranes could be dissociated to non-specific binding levels by 1000-fold excess of competing ligand, whereas binding to guinea-pig lung membranes was only partially dissociated under these conditions. In addition, differences in potency were demonstrated in competition studies with leukotriene E4 and leukotriene C4, although leukotriene D4 and the leukotriene D4-receptor antagonists MK-571 and ICI 204,219 were equipotent in competing for [3H]leukotriene D4-specific binding in all three membranes preparations. In conclusion, the leukotriene D4 receptor in differentiated U937 cell membranes resembles that in human lung, validating the use of this cell line as a suitable source of receptor in the development of potent specific antagonists.

Leukotriene C4 uses a probenecid-sensitive export carrier that does not recognize leukotriene B4

The export of leukotriene (LT) C4 from human eosinophils, a carrier-mediated process that is temperature-dependent and saturable, was characterized further in eosinophils and in two human leukemia cell lines that do not present an intact 5-lipoxygenase pathway. In eosinophils, KG-1 cells, and dimethyl sulfoxide (DMSO)-differentiated HL-60 cells, the respective Q10 values for temperature-dependent LTC4 export were 3.7, 3.3, and 3.4 and for energy of activation were 28.2 kcal/mol, 23.0 kcal/mol, and 27.8 kcal/mol (1 kcal = 4.18 kJ). When human eosinophils, KG-1 cells, and DMSO-differentiated HL-60 cells were preloaded with defined amounts of intracellular LTC4 by incubation with LTA4 and with incremental amounts of a glutathione conjugate, S-dinitrophenyl glutathione (GS-DNP) by sequential incubation with 1-chloro-2,4-dinitrobenzene, GS-DNP inhibited the export of LTC4 in a dose-dependent manner. By plotting the ratio of total GS-DNP (cell retained plus released) to the sum of total GS-DNP plus total LTC4 against the percentage inhibition of LTC4 release, IC40 values of 0.839, 0.803, and 0.841 were obtained for eosinophils, KG-1 cells, and DMSO-differentiated HL-60 cells, respectively. When cells preloaded with LTC4 were resuspended in incremental concentrations of the organic acid transport inhibitor, probenecid, there was a dose-dependent decrease in LTC4 release; GS-DNP and probenecid inhibited LTC4 release in a cumulative fashion, whereas neither inhibited the release of LTB4 from preloaded nondifferentiated HL-60 cells. Therefore, LTC4 export from cells of bone marrow origin occurs through a probenecid-sensitive membrane carrier shared by other glutathione conjugates and distinct from the LTB4 carrier export system.

Relationship between histamine, lipoxygenase and cyclooxygenase products in antigen-induced contraction in guinea-pig tracheal tube preparations

We have used a tracheal tube preparation to study antigen-induced contraction in sensitized guinea pig airways. Treatment with both the cyclooxygenase inhibitor indomethacin and the lipoxygenase inhibitor MK-886 (L-663,536) affected this contraction in preparations with intact epithelium. Indomethacin potentiated and MK-886 inhibited part of the contraction. Leukotriene release from tracheal tubes was measured after antigen challenge, and was found to be significant in preparations with an intact epithelium. When the epithelium was removed, the histamine receptor antagonist mepyramine reduced antigen-induced contraction by 90%. Our results show that when the epithelium is absent, histamine is the most important mediator in the contraction. With the epithelium left intact, the contraction is more complex: both the cyclooxygenase and lipoxygenase pathways are involved, and our findings indicate that eicosanoid production is associated with the airway epithelium.

Effects of ozone on lung mechanics and cyclooxygenase metabolites in dogs

To determine if acute exposure to ozone can cause changes in the production of cyclooxygenase metabolites of arachidonic acid (AA) in the lung which are associated with changes in lung mechanics, we exposed mongrel dogs to 0.5 ppm ozone for two hours. We measured pulmonary resistance (RL) and dynamic compliance (Cdyn) and obtained methacholine dose response curves and bronchoalveolar lavagate (BAL) before and after the exposures. We calculated the provocative dose of methacholine necessary to increase RL 50% (PD50) and analyzed the BAL for four cyclooxygenase metabolites of AA: a stable hydrolysis product of prostacyclin, 6-keto-prostaglandin F1 alpha (6-keto-PgF1 alpha); prostaglandin E2 (PgE2); a stable hydrolysis product of thromboxane A2, thromboxane B2 (TxB2); and prostaglandin F2 alpha (PgF2 alpha). Following ozone exposure, RL increased from 4.75 +/- 1.06 to 6.08 +/- 1.3 cm H2O/L/sec (SEM) (p less than 0.05), Cdyn decreased from 0.0348 +/- 0.0109 TO .0217 +/- .0101 L/cm H2O (p less than 0.05), and PD50 decreased from 4.32 +/- 2.41 to 0.81 +/- 0.49 mg/cc (p less than 0.05). The baseline metabolite levels were as follows: 6-keto PgF1 alpha: 96.1 +/- 28.8 pg/ml; PgE2: 395.8 +/- 67.1 pg/ml; TxB2: 48.5 +/- 11.1 pg/ml; PgF2 alpha: 101.5 +/- 22.6 pg/ml. Ozone had no effect on any of these prostanoids. These studies quantify the magnitude of cyclooxygenase products of AA metabolism in BAL from dog lungs and demonstrate that changes in their levels are not prerequisites for ozone-induced changes in lung mechanics or airway reactivity.

Examination of the role of oxygen free radicals in bronchial asthma in childhood

The antioxidant enzyme activities, the lipid peroxidation level, the parameters of glutathione metabolism, and the proportion of haemoglobin oxidation products were determined during the symptom-free period of childhood bronchial asthma. A decreased catalase activity and a significantly reduced glutathione instability were demonstrated as compared to the controls. The results indicate that antioxidant protection of the haemoglobin molecule in asthmatic children is considerably decreased.

Characterization of the leukotriene D4 receptor in hyperreactive rat lung

A [3H]leukotriene D4 radioreceptor binding assay has been established in rat lung and has been used to fully characterize the leukotriene D4 receptor in lung membranes from an inbred strain of rats displaying non-specific bronchial hyperreactivity. [3H]leukotriene D4 specific binding in this tissue is of high affinity (KD 0.12 nM), saturable (Bmax 42 fmol/mg protein), inhibited by both guanine nucleotide analogues and sodium ions and increased by divalent cations. In addition, Ki values show that agonists, but not antagonists, compete for [3H]leukotriene D4 binding in rat lung with the same potency as they compete for [3H]leukotriene D4 binding in guinea-pig lung, the classical tissue for leukotriene D4 receptor studies. Finally, [3H]leukotriene D4 binding in hyperreactive rat lung has been compared with [3H]leukotriene D4 binding in lung tissue from Fischer rats, which are a less responsive strain.

High-performance liquid chromatographic method for the determination of a novel leukotriene D4 antagonist (MK-0571) in biological specimens

A rapid, sensitive and selective liquid chromatographic procedure was developed to quantitate the levels of a novel leukotriene D4 antagonist, MK-0571 (I), in biological samples. The method involves the addition of an internal standard, an analogue of I, and methanol to the biological matrix. Following centrifugation the supernatant is chromatographed isocratically on a C18 reversed-phase column and the acids are detected with an ultraviolet detector. The sensitivity of the method is such that 50 ng of drug can be quantitated per aliquot of sample. Assays were linear over a 0.06-40.0 micrograms range and exhibited a recovery of 100.5 +/- 7.0% (mean +/- S.D.) over this range. This procedure was utilized to monitor plasma, liver and urinary levels of I in chronic and acute toxicity studies in several animal species.

Stereospecific HPLC method for the quantitation of the enantiomers of MK-0571, a potent leukotriene D4 receptor antagonist, in biological specimens

A stereospecific HPLC bioanalytical method was developed for quantitation of the enantiomers of MK-0571, a leukotriene D4 receptor antagonist. The procedure involves the addition of an internal standard analog to the biological matrix followed by extraction of the free acids into ethyl acetate. The acids are subsequently reacted with the homochiral reagent, (+)-(R)-alpha-(1-naphthyl)ethylamine (NEA) to form diastereomers. Following removal of excess reagent and side products by a dilute acid wash, the NEA-MK-0571 diastereomers are separated on a phenyl urea chiral column using a mobile phase containing hexane, isopropanol, and acetonitrile and are detected with a fluorescence detector. The sensitivity of the method is such that 50 ng of each enantiomer can be quantitated. In the 0.05 to 10 micrograms range the recoveries of the enantiomers of MK-0571 from plasma were 100.4 +/- 7.9% and 100.0 +/- 7.2%. NMR and mass spectral data confirmed the structure of the derivative. The method has been utilized in drug safety evaluation studies to demonstrate enantioselectivity in disposition of the enantiomers of MK-0571 in rats and monkeys but not in mice.

Release of substance P from guinea pig trachea leukotriene D4

Coordinated studies of leukotriene D4 (LTD4)-mediated contractile responses and LTD4-evoked release of the tachykinin substance P (SP) in both intact and epithelium abraded guinea pig tracheal smooth muscle preparations were performed. A partial contribution by axon reflex mechanisms to the magnitude of LTD4-induced tracheal contractions was suggested by a maximum inhibition of 21% and 28% by 5 x 10(-6) M tetrodotoxin (TTX) in abraded and intact preparations, respectively. SP-induced contractions were antagonized by the SP analog [DPro4DTrp7,9]-SP 4-11 in both types of preparation. The SP analog produced 58% and 72% inhibition of contractile responses to 10(-8) M LTD4 in abraded and intact preparations, respectively. Direct measurement of SP release by radioimmunoassay of the bathing medium showed TTX-sensitive LTD4-evoked release of SP. Inhibition by 5 x 10(-6) M TTX of LTD4-evoked SP release was 77%. The SP antagonist produced greater inhibition of LTD4-evoked contractions (58% in abraded, and 72% in intact preparations) than maximum TTX inhibition of LTD4-evoked contractions (21% in abraded, and 28% in intact). However, LTD4 (10(-8) M)-evoked SP release was at least 77% blocked by maximum doses of TTX. We therefore suggest that an additional agent, released by TTX-insensitive mechanisms, but whose contractile effects are also antagonized by [DPro4DTrp7,9]-SP 4-11, may participate in the LTD4 response.

Effects of hydrocortisone and aminophylline on plasma leukotriene C4 levels in patients during an asthmatic attack

To study the role of leukotriene C4(LTC4) and the effect of hydrocortisone and aminophylline on plasma LTC4 levels in patients with asthmatic attacks, we measured LTC4 in plasma of 18 asthmatics during a wheezing attack and of 7 normal subjects. Blood samples were obtained before and after treatment with aminophylline and/or hydrocortisone injections. We extracted LTC4 using a Sep-Pak C18 cartridge for the measurement of LTC4 by radioimmunoassay. The plasma levels of immunoreactive LTC4 (i-LTC4) of the normal subjects were 142 +/- 25 pg/ml (n = 7), while those of nonatopic type asthmatic patients with wheezing attacks were 208 +/- 68 pg/ml (n = 15) (p less than 0.01). Before and after treatment with both hydrocortisone succinate (100 mg) and aminophylline (250 mg), 6 asthmatic patients with wheezing attacks had a mean plasma level of i-LTC4 181 +/- 24 and 132 +/- 18 pg/ml (p less than 0.01), respectively. On the other hand, the treatment with aminophylline 250 mg alone increased the i-LTC4 levels from 178 +/- 19 pg/mg to 213 +/- 16 pg/mg (n = 6)(p less than 0.05), while treatment with hydrocortisone succinate 100 mg decreased the i-LTC4 level 0.05 from 284 +/- 99 pg/ml to 249 +/- 85 pg/ml (n = 4)(p less than 0.05). In conclusion, the present study shows that the i-LTC4 level in venous blood of patients with asthmatic attacks is decreased significantly by treatment with hydrocortisone succinate.

The spontaneous electrical and mechanical activity of human bronchial smooth muscle: its modulation by drugs

1. Tissue taken at operation was used to study the electrical and mechanical properties of human bronchial smooth muscle with intracellular microelectrodes and isometric recording of tension changes. 2. Over 90% of the muscle strips exhibited spontaneous tone and 70% produced spontaneous phasic contractions. The resting membrane potential of the smooth muscle cells ranged between -40 to -50 mV with a mean value of -44.9 +/- 5.2 mV (n = 92 +/- s.d.). Spontaneous oscillations of the membrane potential (slow waves) were observed in 90% of the cells examined. 3. The electrical slow waves, phasic contractions and spontaneous tone were greatly reduced by FPL 55712 (10(-6)-10(-5) M). Indomethacin (1-5 x 10(-5) M), atropine (10(-6) M) or a 5-lipoxygenase inhibitor, AA 861 (5 x 10(-6) M) each reduced spontaneous mechanical tone. Indomethacin and atropine each caused minor reduction in the amplitude of electrical slow waves. 4. Leukotriene C4 (10(-8) M), physostigmine (10(-6) M) and K+-rich physiological salt-solution (containing atropine 10(-6) M) each caused tone development in tissue treated with AA 861 (5 x 10(-6) M). In the case of leukotriene C4 and physostigmine, phasic contractions were superimposed on the developed tone. 5. Electrical field stimulation evoked an excitatory junction potential (e.j.p.) followed by a small group of slow waves. Repetitive field stimulation (2-20 stimuli at 20 Hz) markedly enhanced the amplitude of oscillatory slow waves. FPL 55712 (1.9 x 10(-6) M) abolished the oscillatory slow waves following the e.j.p., and physostigmine (10(-6) M) enhanced the amplitude of the e.j.p. and slow waves. 6. These results indicate that, under in vitro conditions, the electrical activity of human bronchial smooth muscle comprises slow wave discharge which may be related to the spontaneous contractions and generation of basal tone.

Leukotriene C4 in children with atopic asthma. I. Plasma levels in acute asthma

The leukotrienes C4, D4 and E4 are potent biologic mediators, and are thought to play an important role in obstructive airways disease such as asthma. In this study, plasma immunoreactive LTC4 (iLTC4) levels in asthmatic children were measured using radioimmunoassay after Sep-pak extraction in order to determine whether LTC4 is released in vivo during an asthmatic attack. In 10 non-atopic children, the mean +/- SEM of plasma iLTC4 level was 0.031 +/- 0.013 pmol/ml. Significantly higher plasma iLTC4 levels were recognized at all stages in asthmatic children, both in remission (p less than 0.01) and during an attack (p less than 0.01). PaO2 levels during an attack were significantly lower in the high iLTC4 group. In 15 asthmatic children, the plasma iLTC4 levels during an attack (0.134 +/- 0.017 pmol/ml) significantly decreased during recovery (0.078 +/- 0.012 pmol/ml) (p less than 0.05). Plasma iLTC4 levels correlated closely with lung function (p less than 0.01). The high iLTC4 levels in plasma in asthmatic children suggest a role for LTC4 in the pathophysiology of asthma.

Leukotriene C4 in children with atopic asthma. II. Plasma levels in bronchial challenge with specific allergen

Peptide leukotrienes C4, D4 and E4 are considered to be major mediators of hypersensitivity reactions. In this study, immunoreactive leukotriene C4 (iLTC4) in plasma, taken from asthmatic children who had undergone bronchial challenge with a specific allergen, was measured using radioimmunoassay in order to determine whether LTC4 is released in vivo during human allergic reactions. With regard to the bronchial challenge of 10 asthmatic children, plasma iLTC4 levels at the post-challenge stage (0.131 +/- 0.037 pmol/ml) were significantly elevated compared to the pre-challenge stage (0.065 +/- 0.016 pmol/ml) (p less than 0.01). The bronchial response was not directly related to the increased plasma iLTC4 levels, but the strength of the bronchial response did relate to the plasma iLTC4 levels at the pre-challenge (p less than 0.05) and post-challenge (p less than 0.01) states. The pre-challenge levels are relevant to bronchial reactivity, and the post-challenge levels are relevant to bronchoconstriction caused by exposure to allergens. The in vivo release of LTC4 following exposure to a specific allergen suggests that leukotrienes are important in the pathogenesis of asthma.

The effect of inhaled budesonide on the maximal degree of airway narrowing to leukotriene D4 and methacholine in normal subjects in vivo

In normal humans in vivo, maximal airway narrowing to LTD4 is more severe than to methacholine. Moreover, LTD4 heightens the maximal response to methacholine for several days. To investigate whether or not this is due to inflammatory changes in the airway wall, we studied the effects of the corticosteroid budesonide on the dose-response curves to inhaled LTD4 and to methacholine. In a two-period, double-blind, placebo-controlled design, budesonide (400 micrograms twice a day) or placebo was inhaled by eight normal subjects on six consecutive days, with a 3-wk washout. Complete dose-response curves to LTD4 (0.36 to 43 nmol) were performed on Day 5, and to methacholine (1.28 to 655 mumol) on Days 4 and 6 of each period using a validated method. The response was measured by FEV1 and standardized partial expiratory flow-volume curves (V40p), and was expressed as the percent fall from baseline. A maximal response plateau was considered if more than two doses fell within a 5% response range. All subjects reached plateaus to methacholine and to LTD4. Budesonide reduced the maximal response to LTD4 (mean difference with placebo, 7.9% fall for FEV1, and 8.4% fall for V40p; p less than 0.05). During placebo the maximal response to methacholine 24 h after LTD4 was higher than 24 h before (mean change, 2.7% fall in FEV1 and 5.5% fall in V40p; p less than 0.05), but not during budesonide (mean change, -2.5% fall in FEV1 and -0.1% fall in V40p; p greater than 0.2), the changes being significantly different between the two periods (p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

The emergence of potent and selective peptide leukotriene receptor antagonists

Leukotriene (LT) C4, LTD4 and LTE4 collectively comprise the constituents of slow reacting substance of anaphylaxis. Based on their well-documented physiology, and a substantial body of circumstantial evidence, it has been hypothesized that they may be etiologic in allergic diseases, including asthma. Using various chemical approaches, a variety of chemically distinct, highly potent and selective LT antagonists have been disclosed including SKF 104,353, ICI 198,615, L 660,711 and WY 48,252. All are, or will soon, enter clinical trials for asthma. These compounds should provide a viable test for the hypothesis that LTs are etiologic in asthma. The complexity of the disease suggests that clinical expectations for these compounds, or any single entity, should be moderate.

Inhibitory effects of a lipoxygenase inhibitor nordihydroguaiaretic acid on antagonism of leukotriene C4-induced contractions of isolated guinea-pig trachea

We have studied the effects of a lipoxygenase inhibitor nordihydroguaiaretic acid (NDGA) on antagonism of leukotriene (LT) C4-induced contractions of isolated guinea-pig trachea and the results were compared to that of a cyclooxygenase inhibitor indomethacin. NDGA (30 microM) as well as indomethacin (5 microM) inhibited LTC4-induced contractions. But, in the presence of indomethacin NDGA was ineffective to inhibit the LTC4 response, whereas two other lipoxygenase inhibitors, phenidone (3-30 microM) and 5,8,11,14-eicosatetraynoic acid (ETYA, 10 microM), markedly inhibited it. The antagonist action of an LTD4 receptor antagonist FPL55712 against LTC4-induced contractions was significantly reduced by NDGA (10-30 microM), but indomethacin had no effect on it. NDGA possessed the same inhibitory effect on the LTC4 antagonism in the presence of indomethacin, but 0.3 microM phenidone and 1 microM ETYA which did not inhibit the LTC4 response had no effect on it. NDGA also inhibited the relaxant response of isoproterenol on the contraction elicited by 30 nM LTC4, but did not affect those of forskolin and aminophylline. The relaxant response of isoproterenol on the LTC4 response was not inhibited by indomethacin, 0.3 microM phenidone and 1 microM ETYA. In the presence of a gamma-glutamyltranspeptidase inhibitor, L-serine borate (SB, 45 mM), NDGA had no effect on the LTC4 antagonism and the relaxant response of isoproterenol. In contrast, NDGA significantly inhibited the relaxant response of isoproterenol on 30 microM histamine- and 30 microM acetylcholine-induced contractions, but it did not affect the histamine antagonism by a histamine H1-blocker pyrilamine. These results suggest that some putative non-prostanoids are involved in LTC4-induced contractions of guinea-pig trachea and which regulate the effects of LTD4 antagonism and beta-adrenoceptor activation.

Mode of action of calcium antagonists on responses to spasmogens and antigen challenge in human airway smooth muscle

Calcium antagonists have been shown to inhibit exercise-induced asthma. The mechanism of inhibition is unclear, but may involve inhibition of mediator release and/or blockade of the mediator effects. We studied the effects of methoxyverapamil (D600) on human airway responses to spasmogens as well as on histamine release from passively sensitized human lung challenged with ragweed antigen. The concentrations of D600 required to inhibit 50% of the spasmogen responses (IC50) were calculated from the concentration-response relationships and were: histamine 4 x 10(-6) M; KCl 7 x 10(-7) M; leukotriene C4 4 x 10(-5) M; electrical field stimulation 5 x 10(-5) M; and for ragweed antigen in passively sensitized muscle 2 x 10(-6) M. Histamine release by antigen challenge from sensitized lung fragments was not blocked by D600, up to a concentration of 10(-5) M. The data suggest that the contractile effects of agonists are mediated through voltage- and receptor-operated calcium channels. The differential inhibitory effects of D600 on antigen-induced mediator release vs the smooth muscle effects of the various agonists may suggest multiple mechanisms of release or sources of mediators in human airway anaphylaxis.

Mechanism of action of leukotrienes on the guinea pig bronchus

The pharmacological activity of leukotrienes (LT) A4, C4, D4, E4, and histamine was investigated on guinea pig upper and lower bronchi. The contractions of the upper bronchi to histamine, LTA4, C4 and D4 were enhanced by cyclooxygenase inhibitors aspirin (1.67 X 10(-5) and 1.67 X 10(-6) M) and indomethacin (2.8 X 10(-6) and 2.8 X 10(-5) M) whereas the responses to LTE4 were not affected. The myotropic activity of the lower bronchi to all agonists were either very slightly or not at all modified by the presence of cyclooxygenase inhibitors. The thromboxane synthetase inhibitor OKY-046 (1.77 X 10(-5) and 1.77 X 10(-6) M) did not change the responses of higher bronchi to the agonists which suggested that the response of the upper bronchi may be mediated by prostaglandins but not by thromboxanes. The responses of the lower bronchi to leukotrienes A4, C4, D4 and E4 were inhibited by compound OKY-046. Blockade of thromboxane receptors together with inhibition of lipoxygenases by compound L-655,240 (2.53 X 10(-8) to 2.53 X 10(-5) M) had a slight effect on the stimulation of upper and lower bronchi by leukotrienes and histamine. The compound FPL-55712 (1.92 X 10(-6) and 1.92 X 10(-5) M) strongly reduced the contractions of the upper and lower bronchi to leukotrienes but did not affect the responses to histamine. These results suggest that the contractile effects of leukotrienes on upper bronchi is modulated by bronchorelaxant prostaglandins whereas the responses of the lower bronchi are mediated by thromboxanes.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of leukotriene D4 on the mechanical and electrical properties of guinea-pig isolated trachealis

1. The effects of leukotriene D4 (LTD4) on mechanical and electrical activity were examined in guinea-pig isolated trachealis muscle and compared with two other bronchoconstrictors, methacholine and potassium chloride (KCl). 2. LTD4 elicited concentration-dependent increases in tension in trachealis muscle which were slower in time course than responses induced by either methacholine or KCl. The maximum response to LTD4 was approximately 85% of the methacholine maximum. 3. At a concentration close to the EC50 for tension changes, LTD4 had no significant effect on either transmembrane potential or slow wave activity recorded in single trachealis cells. 4. At a concentration close to the EC90 for tension changes, LTD4 caused significant membrane depolarization, transiently reduced the amplitude and increased the frequency of slow wave discharge and ultimately abolished slow wave discharge. LTD4-induced depolarization was less marked, and developed more slowly, than that evoked by either methacholine or KCl. 5. These results show that LTD4 can elicit substantial increases in tension without altering transmembrane potential and are consistent with the view that LTD4 initiates contraction mainly through potential-independent mechanisms. However, at high concentrations the depolarization evoked by LTD4 allows the possibility that potential-dependent mechanisms may contribute to the spasm.

Conscious guinea-pig aerosol model for evaluation of peptide leukotriene antagonists

A new conscious animal model for evaluating leukotriene antagonists is described. The model consists of monitoring the change in the respiratory pattern induced by aerosol administration of various airway constrictors in six guinea pigs secured in a plexiglass chamber by a neck yoke. The animals are pretreated with indomethacin (10 mg/kg, i.p.) and propranolol (5 mg/kg, i.p.) 30 min prior to the challenge. After a 30-min stabilization period, the animals are challenged by various agonists delivered via a Monaghan ultrasonic nebulizer at a flow rate of 2.0 L/min for 5 min. The end point is defined as the onset of slow, labored abdominal breathing (dyspnea) measured in seconds. Peptide leukotrienes (LTs) (30 nM-60 microM) produced concentration-related decreases in time to dyspnea with a rank order of potency of LTD4 greater than LTC4 greater than LTE4. LTD4 was 1,000-fold more potent than histamine or carbachol. Pretreatment of the animals with either FPL55712 or LY171883 delayed the time to reach dyspnea induced by LTD4. In contrast, pyrilamine, cyproheptadine, and phenoxybenzamine failed to alter LTD4-induced dyspnea. The results indicate that this model is useful in assessing the efficacy of LT receptor antagonists in vivo.