Platelet-activating factor (PAF) plays an important role in the immediate asthmatic response in guinea-pig by augmenting the response to histamine.

1. To investigate the role of platelet activating factor (PAF) in the immediate asthmatic response, we examined the bronchial reactivity to histamine after administration of PAF to guinea-pigs or antigen challenge to passively sensitized guinea-pigs. 2. A bolus injection of PAF (20-40 ng kg-1), which did not cause a significant increase in intrathoracic pressure (ITP), augmented the bronchial response to histamine almost 8 fold. This airway hyperreactivity was observed even 1 min after PAF treatment. 3. A subthreshold dose of antigen (0.01 mg kg-1, i.v.) also provoked hyperreactivity to histamine, which became significant 6 and 11 min after the antigen treatment. 4. The specific PAF-antagonists, SM-10661 and CV-6209 (i.v.) dose-dependently inhibited both PAF- and antigen-induced airway hyperreactivities to histamine. 5. These results suggest that PAF plays an important role in antigen-induced acute airway responses by augmenting the activities of spasmogens.     

RP 58802B,a long-acting β2-adrenoceptor agonist: Assessment of antiasthma activity in the guinea-pig in vivo

We have examined the protective actions of RP 58802B, a novel β₂-adrenoceptor agonist, administered by the inhaled and oral routes in the anaesthetized and conscious guinea-pig against bronchospasm induced by histamine or antigen (ovalbumin). We have also examined the effects of RP 58802B on airway reactivity and inflammatory cell infiltration in platelet-activating factor (PAF) (aerosol)-induced bronchial hyperreactivity and on PAF (tracheal instillation)-induced microvascular leakage in the guinea-pig. Nebulized RP 58802B produced a rapid onset and long lasting inhibition of histamine-induced bronchospasm in the anaesthetized guinea-pig (EC₅₀ = 3.2 ± 0.9 μg/ml; duration >90 min). Given orally, RP 58802B (5 mg/kg, 60 min before challenge) produced a >three-fold shift to the right of the dose-response curve and depressed the maximum response to histamine by 39 ± 11%. Increasing the concentration to 25 mg/kg had no further effect. Similar protection was still seen 4 h after oral dosing. In conscious guinea-pigs, RP 58802B (5 or 25 mg/kg, p.o. 60 min before challenge) significantly attenuated antigen-induced dyspnoea with the time to severe dyspnoea increasing from 170 ± 32 to 325 ± 32 s at the higher dose of drug. RP 58802B (10 or 25 mg/kg, p.o. 60 min before exposure to PAF) prevented the development of bronchial hyperreactivity. Although PAF-induced bronchial hyperreactivity was not accompanied by an increase in the number of pulmonary eosinophils, RP 58802B (25 mg/kg p.o.) reduced the numbers of eosinophils recovered by lavage. RP 58802B (10 mg/kg p.o.) significantly inhibited PAF-induced microvascular leakage into guinea-pig lung. These data suggest that RP 58802B, in addition to being a potent and long acting bronchodilator, may have a prophylactic role in preventing bronchial hyperreactivity and in reducing plasma exudation into the lungs.     

Effects of CIS-19, a novel PAF receptor antagonist,on PAF-induced eosinophil recruitment and enhancement of superoxide anion generation in guinea-pigs

We examined the effects of a novel plateletactivating factor (PAF) receptor antagonist, CIS-19 [cis-2-(3,4-dimethoxyphenyl)-6-isopropoxy-7-methoxyl-1-(N-methylformamido)-1,2,3,4-tetrahydronaphthalene], on PAF-induced inflammatory cells recruitment into airways and enhancement of superoxide anion (O _inf2 ^sup– ) generation from cells retrieved by bronchoalveolar lavage (BAL) in urethane-anesthetized guinea-pigs. Administration of PAF (30 ng/kg, Lv.) produced a selective increase of eosinophils into airways, but no significant increase of the number of macrophages, neutrophils or lymphocytes. CIS-19 (2.5 and 5 mg/kg, Lv.) significantly inhibited the eosinophil recruitment induced by PAF. In vitro, PAF, phorbol 12-myristate 13-acetate (PMA) and N-formyl-methionyl-leucyl-phenylalanine (FMLP) directly stimulated generation of O _inf2 ^sup– from BAL cells in a concentration-dependent manner. CIS-19 (10^–7 – 10^–4 M) inhibited production of O _inf2 ^sup– induced by PAF (10^–7 M) in a concentration-dependent manner with an EC₅₀ value of 0.84 M, but not induced by PMA (0.5 g/ml) or FMLP (10^–7 M). Administration of PAF (5 ng/kg, i.v.) enhanced markedly PMA (0.5 g/ml) and FMLP (10^–7 M)-induced generation of O _inf2 ^sup– by 80.2% and 51.3%, respectively. The enhancing effect of PAF was maximal in cells harvested 5 min after the addition of PAF and then declined to baseline level at 60 min. These responses were inhibited by administration of CIS-19 (0.5—2.5 mg/kg, i.v.) or BN 52021(5 mg/kg, i.v.). The results indicate that CIS-19 is potent in inhibition of PAF-induced airway inflammatory response and may have therapeutic potential as an anti-inflammatory drugs.     

Microvascular leakage to platelet activating factor in guinea-pig trachea and bronchi

Conscious guinea-pigs received platelet activating factor (PAF, 0.03-0.25 microgram/kg, i.v.) and colloidal carbon (C, tracer for microvascular leakage). Fifteen min later the animal was killed and C-labelled microvessels (leakage) were detected in the mucosal/submucosal region of tracheal and bronchial sections. PAF was more potent than LTD4 or histamine. The numbers of leaky vessel were dose-related, arterioles and arteries were not affected, leaky vessels were seen from proximal trachea to intrapulmonary bronchi and carbon was not apparent in the alveolar wall. The effect was quick in onset, of short duration, could be repeated, was not produced by lyso-PAF and was unaffected by thrombocytopaenia (produced by an antiserum). Thrombocytopaenia itself did not cause leaky vessels in the airways nor affect histamine responses. Thus, PAF causes an increase in microvascular leakage in the conducting airways, which is not dependent on platelets. The affected vessels are probably postcapillary bronchial venules and PAF may act via an endothelial cell receptor in these microvessels. This leakage effect of PAF in the airways could contribute to features of bronchial asthma.     

Effects of selective phosphodiesterase inhibitors on platelet-activating factor- and antigen-induced airway hyperreactivity, eosinophil accumulation, and microvascular leakage in guinea pigs

There is currently interest in the potential use of selective inhibitors of cyclic nucleotide phosphodiesterases (PDE) in the treatment of asthma. In this study we examined the effects of three selective PDE inhibitors, milrinone (PDE III), rolipram (PDE IV) and zaprinast (PDE V), on the broncoconstriction produced by antigen and histamine, the airway hyperreactivity and microvascular leakage after aerosol exposure to platelet-activating factor (PAF) and antigen, and the antigen-induced eosinophil infiltration in guinea-pig lung. Inhaled rolipram (0.01–10 mg ml^–1) inhibited dose dependently the bronchospasm produced by aerosol antigen (5 mg ml^–1) an anaesthetised, ventilated guinea-pigs. Rolipram (10 mg ml^–1) produced maximal inhibition of antigen-induced bronchoconstriction but only partial inhibition of the response to aerosol histamine (1 mg ml^–1). Milrinone and zaprinast (each 10 mg ml^–1) showed weak, or no, inhibitory effects against bronchoconstriction produced by aerosol antigen or histamine. Pretreatment with rolipram (10 mg kg^–1, i.p.) prevented airway hyperreactivity to histamine which develops 24 h after exposure of conscious guinea-pigs to aerosol PAF (500 g ml^–1) or antigen (5 mg ml^–1). The pulmonary eosinophil infiltration obtained with 24 h of antigen-exposure was inhibited by rolipram. In contrast, milrinone and zaprinast (each 10 mg kg^–1, i.p.) failed to reduce either the airway hyperreactivity of the eosinophil accumulation in these animals. Rolipram (1–10 mg ml^–1) reduced the extravasation of Evans blue after aerosol PAF (500 g ml^–1) at all airway levels while a lower dose (0.1 mg ml^–1) was only effective at intrapulmonary airways. Rolipram (0.01–1 mg ml^–1) markedly reduced airway extravasation produced by inhaled antigen (5 mg ml^–1). Zaprinast (1–10 mg ml^–1) was also effective against airway microvascular leakage produced by aerosol PAF or antigen while milrinone (10 mg ml^–1) had no antiexudative effect. These data support previous suggestions that pharmacological inhibition of PDE IV results in anti-spasmogenic and anti-inflammatory effects in the airways and may be useful in the treatment of asthma.     

Mediator involvement in antigen-induced bronchospasm and microvascular leakage in the airways of ovalbumin sensitized Brown Norway rats

1. To determine which mediators are involved in antigen-induced bronchospasm and microvascular leakage in the airways of ovalbumin sensitised Brown Norway rats we investigated the effect of a histamine H(1) receptor antagonist, mepyramine, a 5-HT receptor antagonist, methysergide, and a cys-leukotriene-1 receptor antagonist, montelukast. 2. Ovalbumin at 1 mg kg(-1) i.v. caused a significant increase in microvascular leakage in the airways and at 3 mg kg(-1) i.v. caused a significant increase in airways resistance. 3. Histamine (1 mg kg(-1) i.v.), 5-HT (0.1 mg kg(-1) i.v.) and leukotriene D(4) (LTD(4), 50 microg kg(-1) i.v.) caused a significant increase in microvascular leakage in the airways. 4. Mepyramine (1 mg kg(-1) i.v.), methysergide (0.1 mg kg(-1) i.v.), or montelukast (30 mg kg(-1) i.v.) inhibited histamine, 5-HT or LTD(4) -induced microvascular leakage respectively. 5. Methysergide (0.1 mg kg(-1) i.v.) reduced ovalbumin-induced microvascular leakage in the trachea and at 0.3 mg kg(-1) i.v. inhibited bronchospasm (38 and 58%, respectively). Montelukast (30 mg kg(-1) p.o.) reduced ovalbumin-induced microvascular leakage in airway tissue to basal levels (78%) and inhibited ovalbumin-induced bronchospasm (50%). Mepyramine (3 mg kg(-1) i.v.) had no effect on ovalbumin-induced leakage or bronchospasm. 6. A combination of all three compounds (mepyramine, methysergide and montelukast) reduced ovalbumin-induced microvascular leakage in airway tissue to basal levels (70 - 78%) and almost completely inhibited bronchospasm (92%). 7. Antigen-induced bronchospasm appears to equally involve the activation of 5-HT and cys-leukotriene-1 receptors whereas ovalbumin-induced microvascular leakage appears to be predominantly mediated by cys-leukotriene-1 receptors.     

Heterogeneous effect of leucotriene CysLT1 receptor antagonists on antigen-induced motor and inflammatory responses in guinea-pig airways

1. The effect of montelukast or MEN91507, selective leucotriene CysLT1 receptor antagonists, on antigen-induced airway inflammation and bronchoconstriction were compared in anaesthetized guinea-pigs. 2. In sensitized animals, ovalbumin (0.3 mg kg(-1), i.v.)-induced microvascular leakage in trachea, intrapulmonary airways, total lung (parenchyma and intrapulmonary airways) and urinary bladder was reduced by MEN91507 (0.01-1 micromol kg(-1), i.v.), whereas montelukast (0.01-1 micromol kg(-1), i.v.) antagonized the effect of the antigen only in the lung and urinary bladder. 3. Ovalbumin (1 mg kg(-1), i.v.)-induced bronchoconstriction was dose dependently antagonized by MEN91507 (10-30 micromol kg(-1), i.v.), whereas the effect of montelukast (0.1-30 micromol kg(-1), i.v.) was marginal (15-30% inhibition). Neither MEN91507 nor montelukast (30 micromol kg(-1), i.v.) affected the bronchoconstrictor response induced by acetylcholine (0.3 micromol kg(-1), i.v.) in sensitized animals. 4. It is concluded that montelukast and MEN91507 display a differential activity against the effect of endogenous leucotrienes, despite the fact that both compounds show a similar antagonist profile against exogenous leucotrienes acting through CysLT1 receptors.     

Rolipram inhibits airway microvascular leakage induced by platelet-activating factor,histamine and bradykinin in guinea-pigs

Abstract— Rolipram (0·1–1000 μg kg^?1, i.v.) reduced the increase in microvascular permeability induced by platelet-activating factor (PAF; 50 ng kg^?1, i.v.) at different sites of the guinea-pig airways. Rolipram (1–100μg kg^?1, i.v.) inhibited histamine (30μg kg^?1, i.v.)-and bradykinin (0·3 μg kg, i.v.)-induced airway microvascular leakage. These effects of rolipram were obtained at doses which inhibit histamine (7–20 μg kg^?1 min^?1)-induced bronchoconstriction (IC50 = 3 ± 1 μg kg, i.v.) without depressing arterial blood pressure in the guinea-pig. Aminophylline (50 mg kg^?1) did not change the effect of PAF. The anti-exudative effect of rolipram is of potential therapeutic value in asthma.     

The role of vasopressin on the effect of U-50,488 to block the development of morphine tolerance and physical dependence

U-50,488, a selective κ-opioid receptor agonist, has been reported to inhibit the development of antinociceptive tolerance to morphine in mice, rats and guinea pigs, but the mechanism involved in this action remains unknown. Since U-50,488 has been reported to supress the plasma vasopressin level, we investigated the role of vasopressin with U-50,488 in the male Sprague Dawley rat in this study. Animals (230–270 g) were chronically treated with morphine (10 mg/kg, i.p.) twice a day for 6 days in order to induce tolerance to antinociceptive effect measured by tail-flick test. Withdrawl symptoms were precipitated by naloxone (10 mg/kg, i.p.) on day 7. U-50,488 (i.p.) or AVP (i.p. or i.c.v.) or U-50,488 and AVP was (were) coadministered with chronic morphine to investigate their effects on morphine tolerance and dependence. We found that coadministration of 8 mg/kg U-50,488 (i.p.) with morphine almost completely block morphine tolerance and partially block withdrawal symptoms. In contrast, coadministration of AVP (0.3 μg/kg, i.p., or 0.01 μg, i.c.v.) with morphine and U-50,488, the effects of U-50,488 to block morphine tolerance and dependence were reversed. In addition, treatment of AVP antagonist (dPTyr(Me)AVP, 0.5 μg/kg, i.p. or 0.5 μg, i.c.v.) has the similar effect as U-50,488 to block morphine tolerance. In summary, the effect of U-50,488 to block morphine tolerance and dependence may relate to its inhibitory effect on AVP release. Received: 20 February 1996 / Accepted: 14 October 1996     

In vitro and in vivo effects of SCA40 on guinea pig airways

SCA40 (6-bromo-8-methylaminoimidazo[1,2-a]- pyrazine-2-carbonitrile), a compound which had been described as an opener of Ca²⁺-dependent large conductance potassium channels (BK_Ca channels), was investigated in comparison with salbutamol for in vitro and in vivo bronchospasmolytic effects and for the ability to reverse airways hyperreactivity in guinea pigs. SCA40 reduced the spontaneous tone of isolated guinea pig tracheal rings with a biphasic concentration-response curve (first phase: pD₂ = 8.0, E_Max = 29.7% of maximal effect; second phase: pD₂ = 6.4, E_Max = 72.6%). The salbutamol curve was monophasic (pD₂ = 8.0, E_Max = 100%). Total lung resistance (R_L) was determined in anaesthetized, ventilated guinea pigs. Bronchoconstriction, measured as an increase in R_L, was elicited in normoreactive animals by i.v. infusion of bombesin (100 ng/kg/min) or by i.v. injection of histamine (1.8–5.6 μg/kg). Airways hyperreactivity was induced by acute i.v. administration of pre-formed immune complexes. Intravenous bolus injections of histamine (2.4 μg/kg) were used to define the sensitivity of the airways prior to and after the exposure to immune complex. Following intratracheal (i.t.) administration, SCA40 reversed bombesin-induced bronchoconstriction with an ED₅₀ of 43 μg/kg (E_Max = 57%). The ED₅₀ for salbutamol was 0.8 μg/kg i.t. (E_Max = 78%). Histamine-induced bronchoconstriction in hyperreactive guinea pigs was inhibited by SCA40 with an ED₅₀ of 13 μg/kg i.t. (E_Max = 82%). Salbutamol completely inhibited histamine-induced bronchospasm with an ED₅₀ of 9 ng/kg i.t. In normoreactive guinea pigs, SCA40 prevented histamine-induced bronchoconstriction with an ED₅₀ of 100 μg/kg i.t.; for salbutamol the ED₅₀ in this test was 0.48 μg/kg i.t. Thus, for both SCA40 and salbutamol, the effects obtained at low doses in hyperreactive guinea pigs represent a true reversal of airways hyperreactivity, whereas at higher doses, anti-hyperreactive and bronchospasmolytic properties may account for the observed effects. In conclusion, SCA40 relaxes guinea pig airways smooth muscle in vitro and in vivo, and it partly reverses airways hyperreactivity. With respect to both potency and efficacy, SCA40 is markedly less active than the β-adrenoceptor agonist salbutamol. Received: 23 August 1996 / Accepted: 11 October 1996     

Effect of long-term infusion of platelet-activating factor on pulmonary responsiveness and morphology in the guinea-pig

The effect of chronic administration of platelet-activating factor (PAF) on airway reactivity, cell recruitment and lung morphology in the guinea-pig has been investigated. Alzet osmotic minipumps delivering either PAF (7.2 mg/kg/14 days) in 0.25% (w/v) bovine serum albumin in saline (saline-BSA), acetylcholine or saline-BSA alone were implanted s.c. in the neck region of guinea-pigs and connected to the jugular vein. In some experiments, implanted and non-implanted animals were treated daily with the PAF antagonist, BN 52021 (15 mg/kg, twice a day, p.o.). On day 15 after minipump implantation, the animals were anesthetized with urethane (1.2 g/kg, i.p.) and tracheal cannula was inserted for mechanical ventilation. Pulmonary inflation pressure (PIP) was monitored and airway responsiveness was assessed by administration of increasing doses of histamine (0.2–100 μg/kg, i.v.). As compared to saline-BSA-treated or non-implanted guinea-pigs, chronic treatment of the animals with PAF induced a significant (p<0.01) increase in airway response. No significant change in airway responsiveness was observed following chronic acetylcholine administration. In contrast, regardless of the treatment of the animals, no change in the threshold dose of histamine inducing alteration in PIP was noted, suggesting that PAF induces bronchopulmonary hyperreactivity rather than hyperresponsiveness. In addition, no significant difference was observed in the in vitro responsiveness to histamine of lung parenchymal strips from animals having received PAF or saline-BSA. Histological evaluation of the lung from guinea-pigs receiving PAF exhibited moderate hyperplasia of airway smooth muscle cells, marked eosinophil infiltration and increase in mast cell number in the peribronchial zone as compared to those from control, acetylcholine- or solvent-treated animals. These alterations were markedly reduced or absent in guinea-pigs implanted with PAF-containing minipumps and concomitantly treated with BN 52021. In conclusion, chronic administration of PAF to guinea-pigs results in airway hyperreactivity to histamine in vivo, associated with structural changes in airway smooth muscle cell mass, but which is unlikely to be secondary to protracted bronchoconstriction.     

Role of nitric oxide, prostaglandins and tyrosine kinase in vascular endothelial growth factor-induced increase in vascular permeability in mouse skin

We investigated role of nitric oxide (NO), prostaglandins (PG) and tyrosine kinase in vascular endothelial growth factor (VEGF)-induced increase in vascular permeability in mouse skin. Subcutaneous injection of VEGF (0.5–2.0 ng/site) induced dose- and time-dependent increase in vascular permeability at the injection site determined by a leakage of Pontamine sky blue. VEGF (1 ng/site)-induced dye leakage was partially inhibited by N^G-nitro-l-arginine methyl ester (an inhibitor for both constitutive and inducible NO synthase) (5 and 10 mg/kg, i.v.) and by aminoguanidine (a selective inducible NO synthase inhibitor) (5–20 mg/kg, i.v.), but not by an inactive enantiomer, N^G-nitro-d-arginine methyl ester (10 mg/kg, i.v.). Pretreatment with an intraperitoneal injection of indomethacin (a nonselective cyclooxygenase inhibitor) (5 mg/kg) or N-(2-cyclohexyloxy-4-nitrophenyl) methanesulphonamide (a cyclooxygenase-2 selective inhibitor) (1–100 μg/kg) almost completely inhibited the effect of VEGF (1 ng/site). Coadministration of PGE₂ (3 and 30 nmol/site) with VEGF did not restore the inhibitory effect of indomethacin on VEGF (1 ng/site)-induced increase in vascular permeability. Lavendustin A (a selective tyrosine kinase inhibitor) (10 and 50 μg/kg, s.c.) dose-relatedly inhibited the VEGF (1 ng/site)-induced increase in dye leakage, whereas its negative control, lavendustin B (10 μg/kg, s.c.) had no effect. Another tyrosine kinase inhibitor, genistein (2.5 mg/kg, s.c.) also inhibited the response. Cycloheximide (a protein biosynthesis inhibitor) (35 mg/kg, s.c.) suppressed the response of VEGF (1 ng/site). Histologically, no cellular infiltration was observed in the area of VEGF injection. These results suggest that increased vascular permeability induced by VEGF is mediated by local production of NO and arachidonic acid metabolites other than PGE₂, which are most probably produced by inducible NO synthase and cyclooxygenase-2, respectively. Protein tyrosine kinase-mediated phosphorylation and synthesis of any new proteins are likely to be required in this effect of VEGF in mouse skin. Received: 18 November 1996 / Accepted: 30 May 1997     

Suppression of PAF-induced bronchoconstriction in the guinea-pig by oxatomide: mechanism of action

Summary Oxatomide potently (ED₅₀ 0.9 mg/kg orally, –2 h) attenuates the reduction of pulmonary tidal volume elicited by PAF (250 ng/kg i.v.) in anaesthetized, ventilated and propranolol-treated guinea-pigs. The increase of the pulmonary inflation pressure elicited by PAF (40 ng/kg i. v.) in such animals, ventilated at a fixed tidal volume, is also significantly reduced by the compound, but substantially higher doses (5 mg/kg i. v., –15 min) are required. The potency of oxatomide in the latter respect (50.4% reduction) is equivalent to that of ketotifen at 5 mg/kg i.v. (55% reduction).In spontaneously breathing, anaesthetized guinea-pigs, oxatomide (5 mg/kg i. p., –1 h) significantly reduces the increase in pulmonary resistance, but not the reduction in dynamic compliance, elicited by PAF (30, 60, 90 ng/kg i. v.), suggesting a pharmacological interference mainly with PAF-induced processes in the larger airways. Changes in arterial blood pressure, haemoconcentration, thrombocytopenia and leukopenia induced by PAF in vivo, contraction of guinea-pig lung parenchymal strips, production of superoxide anion by alveolar macrophages, aggregation and release of ATP by platelets challenged with PAF in vitro are not affected by the compound.These observations suggest that oxatomide attenuates the PAF-induced pulmonary reactions by inhibiting the release and/or the effect of allergic mediators elicited by the phospholipid rather than by a direct antagonism at the PAF receptors.Send offprint requests to F. De Clerck at the above address     

Effect of Hoe 140, a new bradykinin receptor antagonist, on bradykinin- and platelet-activating factor-induced bronchoconstriction and airway microvascular leakage in guinea pig.

We have investigated the effect of a new bradykinin receptor antagonist, Hoe 140 (D-Arg- Hyp3,Thi5,D-Tic7,Oic8]-bradykinin), on bradykinin- and platelet-activating factor (PAF)-induced bronchoconstriction and airway microvascular leakage in anesthetized guinea pigs. Extravasation of Evans blue dye and lung resistance were measured simultaneously. Both i.v. (15 nmol/kg) and inhaled bradykinin (1 mM, 45 breaths) caused a significant increase in lung resistance and leakage of dye at all airway levels. Hoe 140 (100 nmol/kg i.v.) almost completely inhibited these airway responses induced by bradykinin except for dye extravasation in trachea induced by inhaled bradykinin. Inhaled PAF (3 mM, 30 breaths) significantly increased lung resistance and leakage of due at all airway levels, but Hoe 140 had no effect on these responses. Bradykinin-induced bronchoconstriction and airway microvascular leakage are predominantly mediated by activation of B2 receptor, since Hoe 140 is a B2 receptor antagonist. Bradykinin receptor-mediated mechanisms do not play an important role on inhaled PAF-induced bronchoconstriction and microvascular leakage.     

Antagonistic activity of etizolam on platelet-activating factor in vivo experiments

The ability of etizolam, 6-(o-chlorophenyl)-8-ethyl-1-methyl-4H-s-triazolo[3,4-c]thieno[2,3-e] [1,4]diazepine (Y-7131), an anti-anxiety drug, to inhibit platelet-activating factor (PAF)-induced reactions was investigated in experimental animals in vivo. Etizolam (0.01-0.3 mg/kg, i.v.) dose dependently inhibited PAF (0.3 microgram/kg, i.v.)-induced bronchoconstriction (Konzett and R?ssler's method) in guinea pigs, but even at doses as large as 3 mg/kg, i.v., it had no effect on bronchoconstriction induced by histamine, serotonin, acetylcholine, arachidonic acid, bradykinin, angiotensin l or leukotriene D4. Etizolam (0.1-1 mg/kg, i.v.) also dose-dependently reversed PAF (1 microgram/kg, i.v.)-induced hypotension in anesthetized rats. Injection of PAF into the tail veins of mice produced lethal shock within 10-30 min. Etizolam (0.1-3 mg/kg, i.v. and 1-10 mg/kg, p.o.) protected against the lethal effect of PAF (75 micrograms/kg, i.v.) in a dose-dependent manner. These results indicate that etizolam specifically inhibits the action of PAF in vivo.     

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.     

The effect of the specific PAF antagonist BN 52021 and the calcium blocker diltiazem on PAF induced arrhythmogenicity

Platelet-activating factor (PAF) in a concentration of 10(-11) mole per animal decreased the threshold doses for onsets of arrhythmia, ventricular flutters and fibrillation in ouabain induced arrhythmia in guinea-pigs in a statistically significant manner. The specific PAF antagonist BN 52021 (20 mg/kg, orally) completely inhibited the PAF effect for all types of arrhythmia, while the Ca2+ antagonistic drug diltiazem (0.1 mg/kg, i.v.) failed to counteract the PAF action. BN 52021 (20 mg/kg, per os) alone did not exert any effect on ouabain induced arrhythmia, but as expected, diltiazem (0.1 mg/kg, i.v.) showed antiarrhythmic effects. These results confirm the specific PAF antagonistic activity of BN 52021, its usefulness for PAF related cardiac rhythm disturbances and indicate that the method used could be a further useful tool to screen PAF antagonistic substances.     

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.     

Interference of azelastine with anaphylaxis induced by ovalbumin challenge in actively sensitized rats.

The inhibition of the haematological alterations and prevention of death due to systemic anaphylaxis after antigen challenge were investigated in rats after various drug treatments. The i.v. injection of ovalbumin (250 micrograms/kg) into actively sensitized rats induced marked thrombocytopenia and haemoconcentration within 5 min and significant leukocytosis within 30 min, lasting for 2 h after the challenge. Pretreatment with meclizine or terfenadine (15-30 mg/kg i.p.) inhibited antigen-induced haemoconcentration, whereas WEB 2086 (2-10 mg/kg i.p.) and PCA 4248 (5-10 mg/kg p.o.), two platelet-activating factor (PAF) antagonists, interfered with thrombocytopenia only. Azelastine (1-20 mg/kg p.o.) dose dependently inhibited antigen-induced haemoconcentration and thrombocytopenia but failed to block leukocytosis. Azelastine also inhibited the thrombocytopenia observed after the i.v. administration of PAF (4 micrograms/kg). Administration of ovalbumin at a dose of 1.5 mg/kg resulted in a lethal anaphylactic reaction in about 85% of the rats. Pretreatment with WEB 2086 (10 mg/kg i.p.), meclizine (30 mg/kg i.p.) or both increased the survival rate from 15 to 57, 68 and 87%, respectively. Azelastine alone (20 mg/kg p.o.) completely blocked the lethal reaction. It was concluded that the ability of azelastine to antagonize histamine and PAF is important for its effectiveness against anaphylactic shock.     

Haemophilus influenzae induces a potentiated increase in guinea-pig pulmonary resistance to histamine

The human respiratory pathogen Haemophilus influenzae (H.i.) induced bronchial hyperreactivity to histamine (1.0-8.0 micrograms/100 g b.w. i.v.) in vivo in anaesthetized spontaneously breathing guinea-pigs. This hyperreactivity was caused by a potentiated increase in pulmonary resistance. Decreases in dynamic compliance did not differ. Atropine prevented the potentiation at 1.0 and 2.0 micrograms histamine/100 g b.w. These results show that H.i. induces bronchial hyperreactivity in vivo which is mediated by direct and reflex effects of histamine in the central airways.