Lipoxygenase metabolites mediate increased airways responsiveness to histamine after acute platelet activating factor exposure in the guinea-pig

Platelet activating factor (Paf, 0.02 micrograms/kg, i.v. bolus) caused an acute increase in airways responsiveness to histamine in anaesthetized guinea-pigs prepared for recording airways resistance (RL) and dynamic compliance (Cdyn). Aspirin pretreatment (10 mg/kg, i.v.) attenuated the return of airways responsiveness to prechallenge levels. Pretreatment with the combined cyclooxygenase/lipoxygenase inhibitors BW 755C (20 mg/kg, i.v.) and ETYA (20 mg/kg, i.v.), or with the putative cysteinyl-containing leukotriene antagonist FPL 55712 (0.25 mg/kg/min, i.v.), or a Paf antagonist SRI 63441 (2.5 mg/kg, i.v.), prevented Paf-induced increased airways responsiveness. Inhibitors of leukotriene synthesis, BW 755C and ETYA, or action, FPL 55712, had variable effects on Paf-induced bronchoconstriction. These data suggest that lipoxygenase metabolites, possibly leukotrienes, may mediate an acute increase in airways responsiveness to histamine after Paf exposure.     

Effect of a Paf antagonist, WEB 2086, on airway microvascular leakage in the guinea-pig and platelet aggregation in man.

1. The triazolodiazepine WEB 2086 has been evaluated as an antagonist of platelet-activating factor (Paf) by studying its effects on Paf-induced human platelet aggregation and microvascular leakage in guinea-pigs. 2. WEB 2086 inhibited Paf-induced platelet aggregation in platelet-rich plasma in vitro (IC50 = 117 +/- 35 nM, mean +/- s.d.) but had no effect on adenosine 3',5'-diphosphate-induced aggregation. 3. Paf-induced microvascular leakage, measured by the extravasation of intravenously-injected Evans blue dye, was inhibited in a dose-related fashion in the airways and other tissues by WEB 2086, achieving a maximal inhibitory effect at 10 micrograms kg-1, i.v. 4. However, WEB 2086 (10 micrograms kg-1, i.v.) did not inhibit a comparable increase in vascular permeability induced by ovalbumin in sensitized guinea-pigs. 5. We conclude that WEB 2086 is a potent antagonist of Paf and that Paf does not appear to be responsible for antigen-induced microvascular leakage.     

Platelet-activating factor (Paf) antagonist, WEB 2086, protects against Paf-induced hypotension in Macaca fascicularis.

1. The actions of intravenously administered platelet-activating factor (Paf) (0.1-3.33 nmol kg-1) and the effect of a recently described Paf antagonist, WEB 2086, were investigated in the anaesthetized open-chest monkey, Macaca fascicularis. 2. Paf dose-dependently reduced blood pressure, left ventricular pressure (LVP) and its first differential LV dP/dt. 3. Mean pulmonary artery pressure, recorded in three animals, was essentially unchanged by any dose of Paf. 4. WEB 2086 (0.22 mumol kg-1, i.v.) attenuated the Paf-induced changes in BP, LVP and LV dP/dt. The dose-response curve for fall in BP was shifted to the right by one order of magnitude. 5. Histamine-induced cardiovascular changes (systemic hypotension and tachycardia) were not affected by prior administration of WEB 2086. 6. WEB 2086 should be of value in assessing the role of Paf in pathophysiological conditions.     

The booster injection of antigen during active sensitization of guinea-pig modifies the anti-anaphylactic activity of the PAF antagonist WEB 2086.

1. Serum IgG levels of sensitized guinea-pigs bled at various times after the booster injection were evaluated and its capacity to sensitize passively lung strips from normal guinea-pigs assessed. Following the booster injection, both serum IgG and the ability to sensitize passively lung strips increased during the first week and decreased slowly thereafter. 2. The PAF antagonist WEB 2086 (3 mg kg-1, i.v.) blocked the anaphylactic bronchoconstriction induced by intravenous administration of ovalbumin (1 mg kg-1) when guinea-pigs were challenged 2 and 4 days after the booster injection, but became ineffective when tested in guinea-pigs challenged 7, 28 and 56 days after the booster injection. 3. The ability of WEB 2086 to reduce anaphylactic bronchoconstriction of guinea-pigs challenged 2 and 4 days after the booster injection was unrelated to either the selective involvement of one type of immunoglobulin, low IgG titres in sera or a reduced sensitizing capacity. 4. The booster injection, which accounts for the loss of efficacy of WEB 2086 from the fourth day thereafter, probably operates as a PAF-independent inflammatory challenge. 5. The protocol for immunisation and the day of experiment after the booster injection determines the sensitivity of the anaphylactic bronchoconstriction to inhibition of PAF antagonists.     

The effect of Paf antagonists on bronchial hyperresponsiveness induced by Paf, propranolol or indomethacin.

1. Intravenous administration of platelet activating factor, Paf (600 ng kg-1 h-1) to ventilated anaesthetised guinea-pigs induced bronchial hyperresponsiveness to i.v. acetylcholine. 2. Pretreatment of ventilated, anaesthetised guinea-pigs with the beta-adrenoceptor antagonist, propranolol, or the non-steroidal anti-inflammatory drug, indomethacin, induced bronchial hyperresponsiveness to i.v. histamine. 3. Paf-induced bronchial hyperresponsiveness was significantly attenuated by pretreatment with three different Paf antagonists, CV-3988, BN 52021 and WEB 2086. 4. Pretreatment of guinea-pigs with CV-3988, BN 52021 or WEB 2086 at doses inhibiting Paf-induced bronchial hyperresponsiveness, had no significant effect on propranolol or indomethacin-induced bronchial hyperresponsiveness. 5. It is suggested that bronchial hyperresponsiveness induced by propranolol or indomethacin is not secondary to Paf release in the guinea-pig.     

Effects of WEB 2086, a novel antagonist of platelet activating factor, in active and passive anaphylaxis

WEB 2086, a novel specific platelet activating factor (PAF) antagonist derived from triazolodiazepines, inhibited in a dose-related manner the PAF-dependent component of anaphylaxis as well as PAF-induced effects in mice and guinea pigs. In mice a lethal anaphylactic shock and a PAF-induced (100 micrograms/kg i.v.) death was inhibited by i.v. WEB 2086. The ED50 values were 13.6 and 0.37 mg/kg i.v., respectively. In actively sensitized guinea pigs, the anaphylactic lung reaction (bronchoconstriction), but not the corresponding hypotension, was prevented by oral (0.05-0.5 mg/kg) doses of WEB 2086. In contrast, in passively sensitized animals a dose-dependent inhibition of the pulmonary (bronchoconstriction) and blood pressure (hypotension) reaction due to anaphylaxis was achieved by i.v. WEB 2086. Similarly, oral (0.05-0.5 mg/kg) and i.v. (0.005-0.05 mg/kg) WEB 2086 inhibited PAF-induced reduction in respiratory flow (bronchoconstriction) and hypotension in guinea pigs. The ED50 values were 0.070 and 0.066 mg/kg p.o., and 0.017 and 0.015 mg/kg i.v., respectively. In conclusion, PAF seems to play a more major role in passive than in active anaphylaxis in guinea pigs. These results provide further evidence for an important role of PAF in anaphylaxis and support the hypothesis that PAF is involved in asthma and other allergic diseases.     

Bronchial and vascular effects of Paf in the rat isolated lung are completely blocked by WEB 2086, a novel specific Paf antagonist.

1 The effect of the platelet-activating factor (Paf) antagonist, WEB 2086, on Paf-induced increase of pulmonary artery perfusion pressure (Pp), bronchial inflation pressure (Pi) and wet-to-dry lung weight ratios (W/D) was investigated in the rat isolated lung. 2 Lungs were perfused with Krebs-Ringer solution (KRS) as controls or with KRS containing WEB 2086 (0.1, 1.0, 10.0 or 100 micrograms ml-1) and then injected with a bolus of 20 micrograms Paf. 3 A dose-related inhibition of the Paf-induced increase of Pp, Pi and W/D was observed, being almost maximal for the 10.0 micrograms ml-1 and complete for the 100 micrograms ml-1 doses of WEB 2086 when compared to controls. 4 It is concluded that WEB 2086 is a highly effective and specific Paf antagonist in the pulmonary vasculature and bronchial tract.     

Airways hyperreactivity and bronchoconstriction induced by vanadate in the guinea-pig.

1 The characteristics of vanadate-induced bronchoconstriction and airways hyperreactivity were observed in spontaneously breathing anaesthetized guinea-pigs by measurement of airways resistance (Raw) and dynamic lung compliance (Cdyn). Vanadate (0.3-3 mg kg-1 i.v. over 25 min) increased Raw and decreased Cdyn in a reversible, dose-related manner. This action (1 mg kg-1 vanadate) was not inhibited by atropine (1 mg kg-1 i.v.), propranolol (1 mg kg-1 i.v.) or bilateral vagotomy, suggesting a direct effect on the airways smooth muscle. 2 An aerosol of vanadate (10% w/v in H2O) for 3 min decreased Cdyn by 19.5% (P less than 0.05, n = 6) but caused no change in Raw. 3 Histamine (3 micrograms kg-1 i.v.) caused a bronchoconstriction which was enhanced by vanadate in a dose-related manner. This hyperreactivity (after 1 mg kg-1 i.v. vanadate) was unchanged after propranolol or bilateral vagotomy, but was partly blocked by atropine (enhancement by vanadate of the Cdyn change to histamine was diminished, P less than 0.02, n = 3). 4 Bronchoconstrictor responses to acetylcholine (6 micrograms kg-1 i.v.) and 5-hydroxytryptamine (6 micrograms kg-1 i.v.) were also enhanced by vanadate (1 mg kg-1 i.v.) Hyperreactivity after vanadate to the three bronchoconstrictors tested continued during vanadate infusion and was reversed 45 min after cessation of infusion.(ABSTRACT TRUNCATED AT 250 WORDS)     

Limited interference of specific Paf antagonists with hyper-responsiveness to Paf itself of lungs from actively sensitized guinea-pigs.

1. The interference of various platelet-activating factor (Paf) antagonists with Paf- and antigen-induced effects in isolated lungs from actively sensitized guinea-pigs was investigated. 2. WEB 2086 and BN 52021, two antagonists structurally unrelated to Paf, at concentrations 10-100 fold above those exerting a potent and selective inhibition of the effects of Paf in lungs from non-immunized guinea-pigs, failed to inhibit bronchoconstriction and mediator release evoked by the phospholipid when administered into lungs from actively sensitized animals. 3. In contrast to WEB 2086 and BN 52021, antagonists such as Ro 19-3704 and Ro 19-1400, structurally related to the Paf molecule, at concentrations which abrogate the effects of Paf in lungs from non-immunized guinea-pigs, inhibited bronchoconstriction and release of histamine and leukotriene-like material evoked by the intra-arterial administration of Paf into lungs from actively sensitized animals. 4. Ro 19-3704 and Ro 19-1400 also inhibited markedly the release of leukotriene C4 (LTC4)-like material and, to a smaller extent, the histamine secretion induced by 10 micrograms arachidonic acid. 5. CV 6209, another Paf antagonist structurally related to the phospholipid, failed to antagonize its bronchopulmonary and secretory effects in sensitized lungs. 6. All the antagonists used, irrespective of their ability to interfere or not with bronchoconstriction and mediator release triggered by Paf, suppressed oedema formation as measured by the increase in lung wet weight induced by either Paf or ovalbumin. 7. Our results indicate that: (i) the increase in vascular permeability and the subsequent oedema formation on one hand and the bronchopulmonary effects of Paf on the other hand are mediated by different mechanisms; and (ii) active sensitization provokes a marked modification of the lung reactivity to Paf.     

Inhibitory effect of HSR-6071, a new anti-allergic agent, on experimental asthma in rats and guinea-pigs

The experimental asthma caused by IgE antibody in rats was inhibited by HSR-6071 (6-(1-pyrrolidinyl)-N-(1H-tetrazol-5-yl)-2-pyrazinecarboxamide) (0.01-0.1 mg kg-1 i.v.) in a dose-dependent manner. The inhibitory activity of HSR-6071 was more potent than those of disodium cromoglycate and ketotifen, and equipotent with amlexanox. The bronchoconstriction mediated by IgE or IgG antibody in guinea-pigs was also prevented by HSR-6071 (0.3, 1 and 3 mg kg-1 i.v.), amlexanox (3, 10 and 30 mg kg-1 i.v.) and ketotifen (0.1 mg kg-1 i.v.) but not by disodium cromoglycate (10 mg kg-1 i.v.). HSR-6071 was more potent than amlexanox, but less potent than ketotifen. HSR-6071 suppressed antigen-induced histamine and SRS-A release from minced lung tissues of guinea-pigs sensitized passively with rabbit anti-EA serum and was a more potent inhibitor of the release of SRS-A than of histamine. On the other hand, histamine- or acetylcholine-induced bronchoconstriction in guinea-pigs was scarcely affected by HSR-6071 at doses sufficient to inhibit the experimental asthma, but LTD4-induced bronchoconstriction was dramatically inhibited. These results indicate that the inhibitory action on experimental allergic asthma of HSR-6071 may be due to suppression of antigen-induced histamine and SRS-A release from lung tissues and to antagonism of SRS-A action. In addition, HSR-6071 inhibited cyclic AMP phosphodiesterase activity and produced relaxation of the guinea-pig isolated trachea. These pharmacological actions may contribute to the production of the anti-allergic action of HSR-6071.     

Interference of BN 52021, an antagonist of PAF, with different forms of active anaphylaxis in the guinea-pig: importance of the booster injection.

1. BN 52021, an antagonist of platelet activating factor (PAF), was inactive against bronchoconstriction in guinea-pigs sensitized with low amounts of ovalbumin (OA) injected twice, at a 14 day interval and challenged i.v. 7 days later. 2. Serum IgG titers increased for 7 weeks after the booster injection at day 14 and returned to low levels at day 96. 3. Administered by the intratracheal (i.t.) route at 1 mg, BN 52021 failed to inhibit bronchoconstriction induced by the i.t. administration of OA to guinea-pigs tested 7, 28, 56 and 84 days after the booster injection, even when the titers of circulating IgG had declined with time. BN 52021 was also inactive against bronchoconstriction in guinea-pigs boosted at day 98 and tested 7 days later and against contractions and thromboxane (Tx) B2 and histamine release induced by OA-challenged parenchymal lung strips from the boosted guinea-pigs. 4. Sensitized unboosted guinea-pigs displayed reduced IgG serum titers. Used 21 or 70 days after the sensitizing injection, they did develop bronchoconstriction upon the i.t. instillation of OA, which was blocked by BN 52021. The latter also inhibited OA-induced contractions of lung parenchymal strips from these unboosted guinea-pigs. 5. When boosted and non-boosted guinea-pigs received OA i.t. and bronchoalveolar lavage fluid was collected 10 min later, the number of eosinophils increased markedly in boosted, but not in non-boosted guinea-pigs. 6. The booster injection of antigen thus modifies the response of the lung and PAF appears to be relevant for antigen-induced bronchoconstriction in unboosted animals, but loses its major role following the booster injection.     

Interference by the novel PAF-acether antagonist WEB 2086 with the bronchopulmonary responses to PAF-acether and to active and passive anaphylactic shock in guinea-pigs

The interaction between the triazolothienodiazepine WEB 2086 and the in vitro and in vivo bronchopulmonary effects of PAF-acether and active/passive anaphylaxis in the guinea-pig was studied. WEB 2086 (1–100 nM) inhibited PAF-acether (10–100 ng)-induced bronchoconstriction and TXB₂ release from isolated and perfused guinea-pig lungs without affecting the response to 100 μg arachidonic acid. In addition, 1–10 μM WEB 2086 significantly reduced antigen-induced TXB₂ and histamine release from lungs from actively and passively sensitized guinea-pigs. In the presence of the lipoxygenase inhibitor nordihydroguaiaretic acid (NDGA), mepyramine, methysergide, indomethacin and atropine, WEB 2086 (20–50 μM) inhibited by 30–40% the residual contraction of lung parenchyma strips from guinea-pigs actively sensitized by 0.1–10 μg antigen. In vivo, WEB 2086 (0.1–1 mg/kg) reversed or abolished the bronchoconstriction, hypotension, thrombocytopenia and leukopenia evoked by perfusion of PAF-acether (3 or 44 ng/kg per min). At 3 mg/kg, WEB 2086 also markedly decreased the bronchoconstriction and leukopenia induced by 100 μg/kg antigen in mepyramine (5 μg/kg)-treated passively sensitized guinea-pigs. In contrast, WEB 2086 was ineffective against active anaphylaxis in vivo. These results demonstrate that WEB 2086 antagonizes the bronchopulmonary effects due to PAF-acether and to anaphylactic shock in the guinea-pig.     

Inhibitory effect of sodium cromoglycate on pulmonary responses to histamine administered after indomethacin in anaesthetized guinea-pigs.

1. Histamine (2-4 micrograms kg-1 i.v.) increased airways resistance (Raw) and decreased dynamic lung compliance (Cdyn) in urethane-anaesthetized guinea-pigs. The effects on Raw were almost abolished by atropine (0.1 mg kg-1 i.v.) and reduced by vagal cooling (11-16 degrees C). 2. Histamine-induced changes in Raw and Cdyn were significantly (P less than 0.05) enhanced by indomethacin (1 mg kg-1 i.v.). 3. In animals not treated with indomethacin, exposure to an aerosol containing sodium cromoglycate (0.01-2% for 30 s) failed to affect subsequent (3 min) histamine-induced bronchoconstriction. 4. Administration of an aerosol containing low (0.01-0.2%) concentrations of sodium cromoglycate had no effect on the enhanced responses (i.e. hyperreactivity) seen after indomethacin. However, more concentrated sodium cromoglycate aerosols (greater than 0.2%) reduced or abolished the hyperreactivity to histamine seen after indomethacin. 5. It was concluded that sodium cromoglycate can prevent the development of hyperreactivity to histamine, possibly by interacting with some mechanism utilized by both histamine and indomethacin in this model.     

Paf-acether-induced death in mice: involvement of arachidonate metabolites and beta-adrenoceptors.

Intravenous Paf-acether (Paf, 15-80 micrograms kg-1) killed conscious Swiss mice in a dose-dependent manner, without causing platelet aggregation in the lung microvasculature, or pulmonary oedema. Propranolol (0.01-10 mg kg-1, i.p.) potentiated the effects of an LD20 of Paf dose-dependently, while the beta 1-adrenoceptor selective antagonist, metoprolol, was three orders of magnitude less potent in this respect. Salbutamol (1 mg kg-1, i.p.) provided complete protection against an LD80 of Paf. High doses of indomethacin, aspirin, benoxaprofen and FPL 55712 given i.p. failed to inhibit the effects of an LD80 of Paf, while BW 755C (50-100 mg kg-1) exerted a dose-dependent protection and benzydamine (50 mg kg-1) and nordihydroguaiaretic acid (200 mg kg-1) were partially active. Dexamethasone (1-5 mg kg-1, s.c.) exerted a dose-dependent protection, when administered at least 4 h before Paf. In mice anaesthetized with urethane, Paf (1-30 micrograms kg-1) produced hypotension which was not clearly dose-related. The effects of the highest dose were also tested on the resistance of the lungs to inflation and found to produce bronchoconstriction. It may be concluded that pharmacological manipulation of beta 2-adrenoceptors modulates Paf-induced death in mice, while arachidonate metabolites of the cyclo-oxygenase pathway and peptidoleukotrienes do not appear to be involved. However, lipoxygenase products, distinct from peptidoleukotrienes, may play a role in this phenomenon. It is suggested that bronchoconstriction, probably associated with cardiovascular effects, is a major determinant of the acute toxicity of Paf in mice.     

Increased airways responsiveness to histamine induced by platelet activating factor in the guinea-pig: possible role of lipoxygenase metabolites

In anaesthetized guinea-pigs pretreated with propranolol (1 mg/kg, i.v.), platelet activating factor (Paf, 0.02 micrograms/kg, i.v.) caused an acute increase in airways response to histamine (0.5-3.0 micrograms/kg, i.v.) measured as intratracheal pressure. Treatment with the cyclooxygenase inhibitors, aspirin (10 mg/kg, i.v.) or indomethacin (5 mg/kg, i.v.), enhanced the magnitude and duration of this effect but a combined lipoxygenase/cyclooxygenase inhibitor, BW 755C (20 mg/kg, i.v.), prevented the increase in responsiveness. In aspirin treated animals, a putative lipoxygenase inhibitor NDGA (10 mg/kg, i.v.). or atropine methyl nitrate (1 mg/kg, i.v.) or bilateral vagotomy reduced the magnitude of Paf-induced increased histamine responses but did not prevent the effect. Bronchoconstriction induced by Paf was variably influenced by the drug treatments. These data suggest that Paf causes an acute increase in airways responsiveness to histamine in the guinea-pig through a mechanism that may, in part, be dependant on the release of lipoxygenase metabolites.     

BAY u3405 an antagonist of thromboxane A2- and prostaglandin D2-induced bronchoconstriction in the guinea-pig.

1. The novel thromboxane (TX) antagonist, BAY u3405, has been evaluated against bronchoconstriction induced by the TXA2 mimetic U-46619, prostaglandin D2 (PGD2), 5-hydroxytryptamine (5-HT), leukotriene D4 (LTD4) and histamine in the guinea-pig in vivo by use of a modification of the model described by Konzett & Rössler. 2. When given intravenously (i.v.) at 30 or 100 micrograms kg-1, U-46619 caused 80% maximal bronchoconstriction in most animals. In contrast, PGD2 caused a smaller 40%-50% maximal bronchoconstriction at the highest dose tested (300 micrograms kg-1, i.v.). 3. BAY u3405, given intravenously, orally (p.o.) or by aerosol antagonized U-46619-induced bronchoconstriction in a dose-related manner. The approximate ID50 values were 600 micrograms kg-1, i.v., 1.7 mg kg-1 p.o. and 0.1% w/v 20 breaths by aerosol. 4. BAY u3405 had similar inhibitory activities against U-46619-induced bronchoconstriction and hypertension suggesting that it had no preferential activity on the airways. 5. When given intravenously BAY u3405 antagonized the bronchoconstrictor effect of intravenous PGD2 with ID50 values between 30-100 micrograms kg-1. 6. The action of BAY u3405 (10 mg kg-1, p.o.) was long lasting, causing significant inhibition of U-46619-induced bronchoconstriction 7 h after dosing. 7. At 1 mg kg-1, i.v., a dose that abolished the response to U-46619 and PGD2, BAY u3405 had no effect on histamine-, 5-HT- or LTD4-induced bronchoconstriction. 8. BAY u3405 potently and selectively antagonized U-46619- or PGD2-induced bronchoconstriction in the Konzett-Rössler model of guinea-pig lung function.(ABSTRACT TRUNCATED AT 250 WORDS)     

Protective effect of WEB 2086, a novel antagonist of platelet activating factor, in endotoxin shock

WEB 2086, a novel specific platelet activating factor (PAF) antagonist derived from triazolodiazepines, inhibited in a dose-related manner the hypotensive and lethal effect of PAF as well as of E. coli endotoxin in the rat. The hypotension induced by endotoxin (15 mg/kg i.v.) or PAF (30 ng/(kg X min) i.v.) in anaesthetized rats was prevented by oral (1-10 mg/kg) and inhibited or reversed by i.v. (0.1-5.0 mg/kg or 0.1-1.0 mg/kg) doses of WEB 2086. Similar oral and i.v. doses of WEB 2086 protected conscious rats from PAF (15 micrograms/kg i.v.)- and endotoxin (7.5 mg/kg i.v.)-induced death. The results obtained with WEB 2086 confirm that PAF has an important role in the pathophysiology of endotoxin shock. This compound may have a therapeutic effect in human septic shock.     

Quantitative assessment of increased airway microvascular permeability to 125I-labelled plasma fibrinogen induced by platelet activating factor and bradykinin.

1. We have used 125I-labelled fibrinogen (I-FN) in experiments monitoring plasma extravasation from vessels within guinea-pig trachea and peripheral lung tissue in response to platelet activating factor (PAF) and bradykinin (BK). Retained tissue radioactivity derived from I-FN was detected by direct measurement and by autoradiography. 2. Both PAF and BK caused concentration-dependent increases in radioactivity in trachea and peripheral lung, with PAF being approximately 1000 times more potent than BK at both sites. On a wet weight basis, mean tracheal leakage responses to PAF and BK were approximately 6 times and 2 times greater respectively than those in peripheral lung. Furthermore, in trachea, the maximal response to PAF was nearly twice that to BK, although they were approximately equiactive in peripheral lung. The dipeptidyl carboxypeptidase inhibitor, enalapril (1 mg kg-1, i.v.), increased the potency of BK by approximately 40 fold. 3. In trachea, PAF (50 ng kg-1, i.v.)-induced leakage was selectively inhibited by the PAF receptor antagonist, WEB 2086 (5-50 micrograms kg-1), while responses to BK (50 micrograms kg-1, i.v.) were selectively inhibited by the BK2 receptor antagonist NPC 349 (0.5-1 mg kg-1). Neither PAF nor BK-induced leakage were significantly altered by pretreatment with the histamine H1-receptor antagonists mepyramine (10 micrograms kg-1) or ketotifen (50 micrograms kg-1) or the leukotriene receptor antagonist SKF 104353. These data indicate that both agonists caused direct, specific receptor operated increases in tracheal vascular permeability to plasma macromolecules.(ABSTRACT TRUNCATED AT 250 WORDS)     

Inhibition of bronchospasm and ozone-induced airway hyperresponsiveness in the guinea-pig by CDP840, a novel phosphodiesterase type 4 inhibitor.

1. The activity of CDP840, a novel, potent and selective cyclic nucleotide phosphodiesterase type 4 (PDE 4) inhibitor, was evaluated in guinea-pig models (in vitro and in vivo) of bronchospasm, ozone-induced airway hyperresponsiveness (AHR) and non-cholinergic bronchoconstriction. Comparisons were made with (i) other PDE 4 inhibitors: CT1731 (S-enantiomer of CDP840), rolipram, RP73401 and (ii) the clinically used agents salbutamol and theophylline. 2. CDP840 relaxed isolated trachea, under basal tone (EC50 4.5 +/- 1.1 microM) being 17 fold less potent than rolipram (EC50 0.26 +/- 0.13 microM) but attaining the same Emax (83 +/- 6% of the response to 300 microM papaverine). 3. CDP840 relaxed tracheae pre-contracted with carbachol (IC25 39 +/- 9 microM) and histamine (IC25 4 +/- 1 microM) producing monophasic curves. Stereoselectivity was not observed with CT1731 against either carbachol (IC25 33 +/- 11 microM) or histamine (IC25 17 +/- 10 microM). Aminophylline was 1.6 fold (carbachol) and 11 fold (histamine) less potent than CDP840. Rolipram and RP73401 produced tri-phasic relaxation curves but were of similar potency (at the IC25 level) to CDP840 against carbachol (rolipram 18 +/- 5 microM, RP73401 39 +/- 1 microM) whereas against histamine they were approximately 20 fold more potent (rolipram 0.2 +/- 0.1 microM, RP73401 0.2 +/- 0.1 microM). In producing > 30% (carbachol) and > 60% (histamine) relaxation these inhibitors had similar potency and were poor compared to salbutamol. 4. Pre-incubation with CDP840 (10 microM) did not antagonize histamine-induced contraction of isolated trachea; however, it did cause a slight potentiation of the subsequent relaxation to salbutamol (IC50 23 +/- 1 to 15 +/- 2 nM). 5. Pretreatment (1 h) with either CDP840 (1 mg kg-1, i.p. or 3 mg kg-1, i.v.) or rolipram (1 mg kg-1, i.p.) did not bronchodilate or antagonize bronchospasm due to inhaled histamine in anaesthetized, ventilated guinea-pigs. Salbutamol (1 mg kg-1, i.p.) did not bronchodilate but caused a parallel 7 fold rightward shift in the histamine dose-response curve. 6. Stimulation of the vagus nerve in the presence of atropine resulted in a frequency-related bronchoconstriction. CDP840 and rolipram (i.v.) inhibited the response being approximately equipotent (EC50 approximately 10 micrograms kg-1). Neither drug inhibited bronchospasm to inhaled substance P. 7. CDP840 (1-10 micrograms kg-1 i.p.) dose relatedly inhibited ozone-induced bronchoconstriction. CT1731 (1 mg kg-1), rolipram (1 mg kg-1), RP73401 (10 micrograms kg-1) and aminophylline (10 mg kg-1) had no effect. Ozone-induced AHR to inhaled histamine was inhibited by CDP840 in a dose-related manner, 10 micrograms kg-1 abolishing the AHR. This effect was stereoselective as CT1731 was approximately 30 fold less potent than CDP840. Rolipram was approximately 100 fold less potent and RP73401 and aminophylline had no effect. CDP840 was orally active being approximately 10 fold less potent compared to i.p. administration. 8. CDP840 is a poor spasmolytic and anti-spasmogenic agent in response to exogenous mediators; however, it potently inhibits vagally mediated non-cholinergic bronchoconstriction and ozone-induced AHR to histamine. It is possible that regulation of cyclic AMP by PDE 4 contributes to neuronal sensitivity in the airways. Furthermore, CDP840 may suppress AHR without being an overt bronchodilator. Such a profile of activity may have therapeutic benefit in airways diseases such as asthma.     

Antagonism of Paf-induced oedema formation in rabbit skin: a comparison of different antagonists.

1. Eight platelet activating factor (Paf) antagonists were evaluated as inhibitors of oedema formation in rabbit skin induced by intradermal injection of Paf plus prostaglandin E2 (PGE2). Antagonists were tested by both intradermal (i.d.) and intravenous (i.v.) routes. 2. Intradermal injection of two antagonists structurally-related to Paf (SRI 63-675 and CV-3988) resulted in a partial inhibition of Paf-induced oedema formation but at high doses of antagonist, marked agonist activities were detected. CV-3988 administered i.v. inhibited Paf-induced plasma leakage by 73-80%; however, oedema responses to a range of other inflammatory mediators were also reduced, albeit to a lesser extent (40-60%). SRI 63-675 administered i.v. did not significantly inhibit Paf-induced oedema. 3. The antagonist 48740 RP administered either i.d. or i.v. showed partial, but selective, inhibition of Paf-induced oedema formation, although the doses required were high when compared with other antagonists. 4. BN 52021 was a weak Paf antagonist when injected i.d., but following i.v. administration the responses to Paf were inhibited by 63-71%. Responses to all other mediators tested were unaffected. 5. Kadsurenone and its synthetic derivatives, L-652,731 and L-659,989 all blocked responses to Paf in the skin. L-659,989 was the most potent, achieving almost total inhibition when injected i.d. and i.v.; moreover, it was selective for Paf. L-652,731 was more potent than kadsurenone. 6. WEB 2086 given i.d. and i.v. showed similar activity to L-659,989 and it was also selective for Paf-induced oedema formation. 7. These results illustrate that in rabbit skin not all Paf antagonists are selective for Paf, some showing agonist-like activity which can mask antagonist properties. It is suggested that before ascribing a role for endogenous Paf in an inflammatory reaction based on results with antagonists, the activity of the antagonists in the model under investigation should be rigorously established.