The platelet-independent release of thromboxane A2 by Paf-acether from guinea-pig lungs involves mechanisms distinct from those for leukotriene

Comparative efficacy and safety of antiplatelet agents in cerebral ischemic disease: A network meta-analysis

We performed a network meta-analysis (NMA) to enhance the corresponding evidence of the relative efficacy and safety of different antiplatelet agents in cerebral ischemic disease. PubMed and EMBASE were searched systematically for relevant studies. Outcomes were compared using odds ratios and 95% credible intervals. Each agent was ranked according to the value of surface under the cumulative ranking curve (SUCRA). Publication bias was evaluated by funnel plots, while consistency between direct and indirect comparison was analyzed by node-splitting and heat plots. Besides, the clustering technique was used to categorize similar agents. A number of 44 eligible studies with 148 578 patients were included in this NMA. In terms of efficacy (including mortality, recurrent stroke, and vascular event), all six interventions were better than placebo. clopidogrel (Clop) and aspirin (ASA)+Clop were the best two interventions from SUCRA. However, the performance of ASA+Clop declined significantly when considering safety (including myocardial infarction, all-cause withdrawal, and intracranial hemorrhage), especially worse in intracranial hemorrhage. In conclusion, Clop was potentially the most preferable treatment for preventing cerebral ischemic in terms of efficacy and safety. However, the addition of ASA was associated with a potential increase in intracranial hemorrhage, therefore, combination therapy of ASA and Clop should be introduced with caution although it may be more effective than the monotherapy of ASA.

Comparative effects of immediate‐release and extended‐release aspirin on basal and bradykinin‐stimulated excretion of thromboxane and prostacyclin metabolites

A goal of aspirin therapy is to inhibit thromboxane production and platelet aggregation without inhibiting endothelial production of the vasodilator and anti‐thrombotic prostacyclin. This study tested the hypothesis that extended‐release aspirin (NHP‐554C) would have increased selectivity for inhibition of basal and simulated thromboxane formation compared to immediate‐release aspirin (ASA). Thirty‐six healthy subjects were randomized to NHP‐554C or ASA groups. Within each group, subjects were randomized to 5‐day treatment with 81 mg/d, 162.5 mg/d and placebo in a crossover design in which treatment periods were separated by 2‐week washout. On the fifth day of treatment, 81 mg/d and 162.5 mg/d ASA reduced basal urinary excretion of the stable thromboxane metabolite 11‐dehydro‐thromboxane B2 62.3% and 66.2% and basal excretion of the stable prostacyclin metabolite 2,3‐dinor‐6‐keto‐PGF1α 22.8% and 26.5%, respectively, compared to placebo. NHP‐554C 81 mg/d and 162.5 mg/d reduced 11‐dehydro‐thromboxane B2 53% (P = 0.03 vs. ASA 81 mg/d) and 67.9% and 2,3‐dinor‐6‐keto‐PGF1α 13.4% and 18.5%, respectively. NHP‐554C 81 mg/d did not significantly reduce basal excretion of the prostacyclin metabolite. Both doses of ASA and NHP significantly reduced excretion of both thromboxane and prostacyclin metabolites following intravenous bradykinin. During NHP‐554C 162.5 mg/d, but not during ASA, bradykinin significantly increased urinary 2,3‐dinor‐6‐keto‐PGF1α. Nevertheless, 11‐dehydro‐thromboxane B2 and 2,3‐dinor‐6‐keto‐PGF1α responses to bradykinin were statistically similar during ASA and NHP‐554C. In conclusion, at doses of 81 and 162.5 mg/d immediate‐ and extended‐release aspirin selectively decrease basal thromboxane production. Both forms of aspirin decrease bradykinin‐stimulated thromboxane and prostacyclin production, but some stimulated prostacyclin production remains during treatment with NHP‐554C.

Bradykinin and capsaicin induced airways obstruction in the guinea pig are platelet dependent

INTRODUCTION

Airways obstruction induced by intravenously administered bradykinin is abolished in guinea pigs treated with indomethacin, which has been shown to be, at least in part thromboxane dependent. As thromboxane is primarily generated from circulating platelets, we investigated whether airways obstruction induced by bradykinin, and other spasmogens, is platelet dependent and the role platelet aggregation played in this response.

METHODS

Guinea pigs were chronically treated with busulfan to induce thrombocytopenia. Total lung resistance was measured in anaesthetised and mechanically ventilated control and thrombocytopaenic animals to various stimuli that induce airways obstruction. In other experiments, platelet aggregation was assessed in vitro in response to the same stimuli: guinea pigs were anaesthetized, blood was collected and centrifuged to generate firstly platelet-rich plasma and then platelet-poor plasma. Platelets were resuspended in HEPES buffer and platelet aggregation was assessed.

RESULTS

Busulfan treatment significantly reduced the number of circulating platelets in guinea-pigs by 85.5%, but had no significant effect on the number of circulating leukocytes. Treatment with busulfan had no significant effect on bronchoconstriction induced by the direct acting spasmogens histamine or methacholine. However, platelet depletion significantly increased airways obstruction induced by Substance P, but caused a significant reduction in airways obstruction induced by bradykinin, bombesin or capsaicin (P < 0.05). None of these stimuli however were able to exhibit a direct effect on platelet aggregation in vitro. Moreover, busulfan did not significantly alter the contractility of guinea-pig isolated trachea in response to capsaicin.

CONCLUSION

Airways obstruction induced by bombesin, capsaicin and bradykinin is platelet dependent, but not secondary to platelet aggregation.

Effect of DP-1904, a thromboxane synthetase inhibitor, on antigen- and spasmogen-induced bronchoconstriction in rodents

The effect of DP-1904 [6-(1-imidazolylmethyl)-5,6,7,8-tetra-hydronaphthalene-2-car boxylic acid hydrochloride], a selective thromboxane synthetase inhibitor, was examined on antigen- and spasmogen-induced bronchoconstriction in rodents. Oral administration of DP-1904 (1, 3, 10 mg/kg) as well as OKY-046 (sodium (E)-3[4-(1-imidazolylmethyl)-phenyl]-2-propanoate, 100 mg/kg), significantly inhibited immunoglobulin G-mediated bronchoconstriction in actively sensitized guinea pigs. Immunoglobulin E-mediated bronchoconstriction in actively sensitized rats was also inhibited by both DP-1904 (1, 10 mg/kg) and OKY-046 (100 mg/kg). DP-1904 (3-30 mg/kg) and OKY-046 (30 mg/kg) suppressed leukotriene D4-induced bronchoconstriction in guinea pigs. In these models, the endogenous levels of thromboxanes significantly increased following the stimulus (antigen and leukotriene D4). DP-1904 (10 mg/kg) inhibited the increase in thromboxane level in both plasma and bronchial alveolar lavage fluid. These actions of DP-1904 persisted for more than 12 h, indicating a long-lasting effect of DP-1904 on bronchoconstriction. The results showed that the biological activity of DP-1904 in our rodents models is more potent than that of OKY-046 (Ozagrel), which is available as an anti-asthma agent in Japan.

Anti-inflammatory, analgesic, antipyretic and related properties of meloxicam, a new non-steroidal anti-inflammatory agent with favourable gastrointestinal tolerance

The anti-inflammatory, analgesic and antipyretic properties of the new non-steroidal anti-inflammatory agent, meloxicam, were investigated in a variety of animal models and compared with the properties of piroxicam, diclofenac, indomethacin and several other NSAIDs. With respect to the total effect of a single oral dose, the anti-exudative effect of meloxicam on carrageenan-induced oedema in the rat exceeded that of all the NSAIDs included in the comparison. Additionally, meloxicam showed the greatest potency of all the compounds examined with respect to adjuvant-induced arthritis in the rat, the granuloma pouch model and the cotton pellet test in the rat. Unlike indomethacin, in the carrageenan pleurisy model in the rat, meloxicam caused both a dose-dependent reduction in exudate volume and also inhibition of leucocyte migration. Meloxicam showed a strong and lasting effect on inflammatory pain in the rat. Like other NSAIDs, but unlike dipyrone, meloxicam had no effect in the hot plate and tail clamp tests, which are used to identify weak central analgesic effects. Unlike dipyrone and like indomethacin, meloxicam had no effect in a model of visceral distention pain. In common with other NSAIDs, meloxicam had no influence on the body temperature of normothermic rats in the anti-inflammatory dose range, but did reduce yeast-induced fever in the rat in a dose-dependent manner. Like piroxicam, meloxicam had a uricosuric effect on rats treated with oxonic acid. Low-dose meloxicam inhibited both bradykinin-induced and PAF-induced bronchospasm in the guinea-pig, but had no effect on acetylcholine-induced bronchospasm. Piroxicam had greater ulcerogenic effects in the rat stomach than meloxicam. The therapeutic range of meloxicam in the rat, with regard to inhibition of adjuvant arthritis, was several times greater than that of piroxicam, indomethacin, diclofenac and naproxen.

Studies on the mechanism of PAF-induced vasopermeability in rat lungs

The present study evaluated the effect of platelet activating factor (PAF) instilled into rat airways on vascular permeability assessed in isolated lung tissues by Evans blue (EB)-labelled plasma protein extravasation. It was found that intratracheal instillation of PAF induces a dose-dependent increase of EB extravasation in the bronchi (upper and inner) but not in the lung parenchyma. The contribution of eicosanoids to PAF-induced increase of vascular permeability was investigated by treating the animals with selected inhibitors prior to PAF administration. Mepacrine (5 mg/kg), L-663,536 (10 mg/kg), indomethacin (4 mg/kg) and dazoxiben (10 mg/kg) significantly reduced EB extravasation in the bronchi. The PAF antagonists BN-52021 (5 mg/kg), WEB-2086 (1 mg/kg), WEB-2170 (5 mg/kg) and PCA-4248 (3 mg/kg) were all effective in reducing the extravasation. These results suggest that PAF-induced increase of vascular permeability in rat bronchi is mediated by cyclooxygenase and lipoxygenase products of arachidonic acid metabolism.

Mechanisms of pulmonary vasoconstriction and bronchoconstriction produced by PAF in the guinea-pig: role of platelets and cyclo-oxygenase metabolites

1. The mechanisms of action of platelet activating factor (PAF) in the bronchial and cardiovascular systems have not yet been fully elucidated. In order to characterize better and to ascertain whether the effects of PAF in both these systems may be ascribed to the same mechanisms, we examined the actions of PAF in the heart-lung preparation of guinea-pig (HLP). The role of platelets and of cyclo-oxygenase metabolites was investigated. 2. In HLPs perfused with autologous blood, bolus injections of PAF (4-32 ng) produced major effects at the pulmonary vascular and bronchial levels. Both dose-related pulmonary vascular hypertension and bronchoconstriction produced by PAF were diminished to the same extent (46% and, respectively, 47%) when HLPs were perfused with a medium consisting of homologous red blood cells suspended in physiological solution containing 3.5% dextran (RBC). This suggests that the effects of PAF partially depend on the presence of formed elements. 3. When indomethacin (30 microM) was added to the perfusing blood, the dose-response curve for the pulmonary hypertensive responses produced by PAF was strongly reduced (90%) in comparison to control preparations, whereas the bronchoconstrictor effects of PAF were only partially diminished (23%). These data constitute direct evidence that products of the cyclo-oxygenase pathway exert a major role in the vascular, rather than in the bronchial actions of PAF. 4. In HLPs perfused with RBC containing indomethacin (30 microM), the pulmonary vascular hypertensive responses produced by PAF were almost completely abolished, thus indicating that cyclo-oxygenase products from tissues are involved in these effects. Conversely, PAF administration continued to cause dose-related bronchoconstrictor responses that were reduced only partially in comparison with HLPs perfused with RBC in the absence of the cyclo-oxygenase inhibitor. This implies that PAF also has direct action on the bronchoconstriction evoked.5. At the cardiac level, administration of PAF in HLPs perfused with blood caused a dose-related increase in right atrial pressure accompanied by a decrease in left atrial pressure and cardiac output,which were completely suppressed or attenuated by the absence of formed elements and the addition of indomethacin. This suggests that the progressive heart impairment is secondary to the severe pulmonary hypertension induced by PAF.6. The results of this study performed in the heart-lung preparation of the guinea-pig, which made it possible to simultaneously record cardiovascular and bronchial parameters, indicate that various components are involved in the responses produced by PAF. It is suggested that different mechanisms depending on the relative contribution of these components may account for the PAF-induced effects at the pulmonary vascular and airway levels.

Role of thromboxane A2 and platelet-activating factor in allergic bronchoconstriction in guinea pig airway in vivo

Membrane-derived lipid mediators have been considered to play a major role in pathogenesis of bronchial asthma. However, the importance of and the interactions among each mediator are still unclear. We examined the role of thromboxane A2 (TXA2) and platelet-activating factor (PAF) in immediate asthmatic response (IAR) and interactions between these lipid mediators in guinea pig airway in vivo using a specific TXA2 antagonist S-1452 and a specific PAF antagonist Y-24180. We confirmed the activity of each antagonist, as S-1452 and Y-24180 significantly and dose-dependently inhibited bronchoconstriction induced by respective agonist inhalation. S-1452 inhibited IAR but Y-24180 did not, indicating that TXA2 plays a major role in IAR but PAF does not. S-1452 significantly inhibited PAF-induced bronchoconstriction but Y-24180 did not inhibit synthesized TXA2 (STA2)-induced bronchoconstriction, showing that the bronchoconstrictive effect of PAF is at least in part dependent on secondarily released TXA2, but TXA2 does not induce PAF production.

[Asthma: an inflammatory disease]

Asthma is a bronchial disease, which is often allergic. Progress in the knowledge of its physiopathology allowed the demonstration of the local bronchial inflammatory process. The arguments supporting this new approach are experimental, clinical and therapeutical. This new approach is confirmed by the real therapeutical revolution, bronchial anti-inflammatory treatment based on inhaled corticosteroids. Furthermore, this approach was clearly synthetized by a new definition of asthma, which resulted from a recent international consensus.

Role of leukotrienes and platelet activating factor in allergic bronchoconstriction and their interactions in guinea pig airway in vivo

Membrane-derived lipid mediators have been considered to play a major role in pathogenesis of bronchial asthma. Recently specific antagonists and synthetase inhibitors of some chemical mediators have been developed and many studies on their anti-asthmatic effects are ongoing. But the importance of and the interactions of each mediator are still unclear. We examined the role of leukotrienes (LTs) and platelet activating factor (PAF) in immediate asthmatic response (IAR) and interactions between these lipid mediators in guinea pig airways in vivo using a specific LTs antagonist AS-35 and a specific PAF antagonist Y-24180. We confirmed the activity of each antagonist, as AS-35 and Y-24180 inhibited bronchoconstriction induced by respective agonist inhalation. AS-35 inhibition IAR but Y-24180 did not, indicating that LTs play a major role in IAR but PAF does not. AS-35 did not influence PAF-induced bronchoconstriction and Y-24180 did not inhibit LTs-induced bronchoconstriction, showing that there is no interaction between LTs and PAF.

Sensitization of peripheral afferent fibres in the in vitro neonatal rat spinal cord-tail by bradykinin and prostaglandins

The sensitization of peripheral nociceptors by different prostaglandins was studied in an in vitro preparation of the neonatal spinal cord with functionally attached tail. Nociceptors in the rat tail were activated by chemical (bradykinin, capsaicin) and thermal (heated saline) stimuli and responses were recorded as a depolarization of a ventral root in the lumbar region of the spinal cord (L3-L5). Responses evoked by bradykinin, capsaicin or submaximal thermal stimulation were enhanced in the presence of prostaglandin E1, prostaglandin E2, prostaglandin F2 alpha, prostaglandin I2 and the stable prostaglandin I2 analogue cicaprost, but not by prostaglandin D2. Cyclic AMP and threshold concentrations of bradykinin also induced an enhancement of responses to chemical and thermal stimuli. Responses evoked by small concentrations of bradykinin on unsensitized preparations were reduced by indomethacin or aspirin, whereas responses to maximal concentrations of bradykinin were not affected. Immunocytochemical localization of protein gene product 9.5 and growth associated protein 43 indicated that the neuronal innervation of subepidermal skin layers was preserved in the tail following removal of the most superficial skin layers which was performed in order to facilitate drug access to peripheral nerve endings. These results indicate that different prostaglandins and cyclic AMP sensitize peripheral nerve endings to noxious stimulation without directly activating nociceptors. The stimulation of nociceptors by bradykinin was only partially mediated via arachidonic acid metabolites whereas bradykinin-induced sensitization was independent of cyclo-oxygenase activity.

Hydrogen peroxide-induced broncho- and vasoconstriction in the isolated perfused and ventilated guinea pig lung

The effect of hydrogen peroxide on perfusion flow, airway conductance (Gaw) and dynamic compliance (Cdyn of isolated perfused and ventilated guinea pig lungs was investigated. Hydrogen peroxide (50 microM in the perfusion buffer) induced a decrease in Gaw and Cdyn and perfusion flow during 5 min. of exposure. Hydrogen peroxide also caused an increase in the levels of thromboxane in the perfusate of the lung. The constrictor effects as well as the formation of thromboxane were inhibited by the cyclooxygenase inhibitor ibuprofen (50 microM). The thromboxane/prostaglandin endoperoxide receptor antagonist L-670,596 (1 microM) abolished the effects of hydrogen peroxide on perfusion flow, Gaw and Cdyn, but did not affect the formation of thromboxane. The thromboxane-synthetase inhibitor carboxyheptylimidazole (100 microM) reduced both the hydrogen peroxide-induced formation of thromboxane and vaso- and bronchoconstriction, suggesting a predominant role for thromboxane A2 versus prostaglandin H2 in these effects. A role for platelet-activating factor in mediating the effect of hydrogen peroxide could not be supported, as the platelet-activating factor receptor antagonist WEB 2086 (10 microM) did not affect hydrogen peroxide induced vaso- and brochoconstriction. The results of this study show that hydrogen peroxide induces thromboxane A2 mediated vaso- and bronchoconstriction in the isolated perfused and ventilated guinea pig lung. Platelet-activating factor does not appear to play a significant role in the hydrogen peroxide-induced vaso- and bronchoconstriction. Our results also suggest that the perfused guinea pig lung is more sensitive to hydrogen peroxide than the perfused rat lung.

Interference of a neutrophil recruitment inhibitory factor upon the accumulation of inflammatory cells and airway hyperreactivity in sensitized guinea-pigs after intranasal antigen challenge

1. A neutrophil recruitment inhibitory factor (NRIF) recovered from the crude supernatant of lipopolysaccharide (LPS)-stimulated macrophages inhibited neutrophil migration following both intratracheal and intravenous administration of LPS, but did not alter the pattern of leukopenia/leucocytosis induced by intravenous LPS. 2. The correlation between airway infiltration by inflammatory cells and hyperreactivity in lungs from actively sensitized and challenged guinea-pigs was investigated by use of NRIF. 3. Increased eosinophil counts were found in the bronchoalveolar lavage fluid from guinea-pigs sensitized with 10 micrograms ovalbumin and challenged at day 14 by the intranasal administration of the antigen. The increase was evident 5 h after challenge and persisted at 24 h. Neutrophil numbers were also increased at this time. Pretreatment with NRIF suppressed the leucocyte increase in the bronchoalveolar lavage fluid. 4. Bronchoconstriction and histamine release induced by 3 ng PAF injected into the isolated lungs were increased in challenged guinea-pigs as compared to sensitized but unchallenged controls. Pretreatment of the animals with NRIF did not interfere with this response, but significantly reduced the bronchoconstriction induced by ovalbumin injection. 5. Even though the increased number of inflammatory cells in bronchoalveolar lavage and airway hyperresponsiveness were concomitant, NRIF inhibited cellular infiltration but failed to alter airway hyperreactivity to PAF, demonstrating that these events may occur independently. Conversely, the inhibition of antigen-induced bronchoconstriction by NRIF suggests that this response is dependent upon the emigration of granulocytes.

Inhibitory effect of a peptide leukotriene antagonist ONO-1078 on LTD4- and antigen-induced thromboxane B2 production in guinea pig lungs

The effect of a peptide leukotriene receptor antagonist ONO-1078 on the production of thromboxane (Tx) B2 induced by leukotriene (LT) D4 and antigen challenge was examined in guinea pig lungs. LTD4 (1-1,000 nM) induced a concentration-dependent production of TxB2 in non-sensitized guinea pig lungs and ovalbumin challenge (0.01-100 micrograms/ml) produced TxB2 and peptide leukotrienes in a concentration-dependent manner in ovalbumin-sensitized guinea pig lungs. ONO-1078 inhibited LTD4 (100 nM)-induced TxB2 production with the IC50 value of 0.24 microM. Furthermore, ONO-1078 inhibited antigen (10 micrograms/ml)-induced TxB2 production with the IC50 value of 0.14 microM without effect on the production of peptide leukotrienes. These results suggest that ONO-1078 may prevent the antigen-induced production of TxB2 through the blockade of the activation of receptors by endogenously generated peptide leukotrienes.

Guinea-pig treatment with pertussis toxin suppresses macrophage-dependent bronchoconstriction by fMLP and fails to inhibit the effects of PAF

1. Bronchoconstriction and thromboxane B2 (TxB2) release following the intra-tracheal administration of the secretagogue N-formyl-L-methionyl-L-leucyl-L-phenylalanine (fMLP) to lungs from pertussis toxin-treated guinea-pigs in vivo and in vitro were inhibited as compared to saline-treated animals, under conditions where the responses to PAF were modified less effectively. 2. The cell target accounting for bronchoconstriction by fMLP and for inhibition by pertussis toxin is located in the airways and is probably the alveolar macrophage. Indeed (a) fMLP-induced superoxide anions and TxB2 formation by alveolar macrophages were inhibited by pertussis toxin given in vivo; (b) Gi proteins of membranes from alveolar macrophages were ADP-ribosylated in vivo by pertussis toxin and (c) bronchoconstriction and TxB2 release in response to the intra-tracheal administration of fMLP to lungs from pertussis toxin-treated animals were restored when alveolar macrophages from control guinea-pigs were transferred into the airways of pertussis toxin-treated animals before lung isolation. 3. Pertussis toxin administered to guinea-pigs in vivo, reduced the subsequent TxB2 formation and superoxide anion release by alveolar macrophages stimulated with PAF, but failed to inhibit PAF-induced bronchoconstriction. 4. Formation of TxB2 by alveolar macrophages following the intra-tracheal administration of fMLP accounts for bronchoconstriction and requires pertussis toxin-sensitive Gi proteins. PAF operates via a different mechanism, which is independent of Gi-like protein and involves mediators other than TxB2 and superoxide anions.

Effects of PAF on excitatory neuro-effector transmission in dog airways

1. Effects of PAF on excitatory neuro-effector transmission in smooth muscle cells of mucosa-free trachea and epithelium-intact bronchiole of the dog were investigated, by isometric tension recording, microelectrode and double sucrose-gap methods. 2. PAF (10(-11)-10(-7) M) dose-dependently enhanced the amplitude of contraction evoked by repetitive field stimulations (10 stimuli at 20 Hz) in both tracheal and bronchiolar tissues. At higher concentrations PAF (> 10(-8) M) increased the amplitude of contraction to a greater extent in the bronchiole than in the trachea. 3. In both muscle tissues, in parallel to the amplitude of contraction, PAF markedly enhanced the amplitude of excitatory junction potentials (e.j.ps) evoked by a single field stimulation in a dose-dependent manner, with no change in the resting membrane potential or input membrane resistance of the smooth muscle cells. PAF (5 x 10(-7) M) enhanced the amplitude of e.j.p. to a greater extent in the bronchiole than in the trachealis. In contrast, lyso-PAF (10(-10)-10(-7) M) showed no effect on e.j.p. amplitude in bronchiolar tissues. At a high concentration (10(-7) M) lyso-PAF slightly enhanced the e.j.p. amplitude in tracheal tissue, however the lyso-PAF induced stimulation of e.j.p. amplitude in the trachea was small compared to that of PAF. 4. PAF (10(-7) M) had no effect on the membrane depolarization induced by acetylcholine (ACh, 10(-9)-10(-5) M) and carbachol (10(-9)-10(-5) M) in tracheal smooth muscle cells. 5. The PAF-antagonists CV3988 (5 x i0-7 M) or WEB2086 (5 x 10-7 M) significantly enhanced the e.j.p. amplitude themselves, PAF (5 x 10-8 M) further enhanced the ej.p. amplitude in the presence of WEB2086 (5 x l0-7 M) but not CV3988 (5 x 10-7 M). In contrast, the new PAF-antagonist, E 6123(5 x l0-8 M), did not affect the ej.p. amplitude itself, and completely inhibited the increase in ej.p. amplitude caused by 5 x 10-8 M PAF. On the other hand, in the presence of the Hi-antagonist,mepyramine, PAF (5 X 10-8 M) further enhanced the ej.p. amplitude.6. The leukotriene synthesis inhibitor AA-861 (10-6 M) or leukotriene antagonist ONO1078 (10-7 M)inhibited the increase in ej.p. amplitude caused by 5 X 10-8 M PAF, respectively.7. In the presence of AA-861 (10-6 M), leukotriene B4 (LTB4, 10-' M) or LTD4 (10-8 M) slightly, and LTC4 (10- M) markedly enhanced the ej.p. amplitude. In contrast, LTE4 (10-8 M) significantly suppressed the e.j.p. amplitude.8. PAF (5 x 10-8 M) attenuated the depression phenomena of ej.ps observed during double stimulus experiments at different time intervals (5-10 s), but had no effect on the summation of ej.ps during repetitive field stimulation at a high frequency (20 Hz) in the trachealis.9. These results indicate that PAF potentiates excitatory neuro-effector transmission mainly through stimulating the release of lipoxygenase products, mainly LTC4 in the dog airway smooth muscle tissues.

Characterization of thromboxane A2/prostaglandin H2 receptors and histamine H1 receptors in cultured guinea-pig tracheal smooth-muscle cells

We characterized thromboxane A2/prostaglandin H2 (TXA2/PGH2) receptors and histamine H1 receptors in Guinea-pig cultured tracheal smooth-muscle cells (TSMC). [3H]SQ 29,548 (a TXA2 antagonist)-binding sites were saturable and a high affinity with a dissociation constant of 6.2 +/- 0.60 nM (mean +/- S.E.) and a receptor density of 46 +/- 4.6 fmol/10(6) cells. [3H]SQ 29548 binding was completely inhibited by TXA2 mimetics or antagonists. Intracellular calcium concentration ([Ca2+]i) in TSMC was increased with U46619 stimulation and the increase was attenuated by TXA2 antagonists, the potencies of which correlated with those inhibiting the activities of the [3H]SQ 29548 binding. [3H]Mepyramine (a H1 antagonist)-binding sites were also present in TSMC. [3H]Mepyramine had a single class of low-affinity-binding sites with a dissociation constant of 2.6 +/- 0.081 microM and a receptor density of 10.6 +/- 0.11 nmol/mg protein. [3H]Mepyramine binding in TSMC membrane was inhibited by H1 antagonists, but not by H2 antagonists. The inhibition constants of mepyramine in TSMC were 910-times lower than those in tracheal membranes. In contrast, the histamine-induced increase in [Ca2+]i in TSMC was inhibited in the presence of low concentrations of H1 antagonists. All these observations provide evidence that TXA2/PGH2 receptors, mepyramine-binding sites and/or H1 receptors are expressed in cultured TSMC.

Effect of human recombinant interleukin-5 on in vitro responsiveness to PAF of lung from actively sensitized guinea-pigs

1. The intra-tracheal (i.t.) administration of human recombinant interleukin-5 (rhIL-5; 100 or 300 ng) to isolated perfused lungs from guinea-pigs actively sensitized to ovalbumin induced an increased bronchoconstriction and release of thromboxane A2 (TXA2) and histamine into the lung effluent following the subsequent (10 min) intra-arterial injection of platelet-activating factor (PAF). Lung responses to 5-hydroxytryptamine were unaffected by rhIL-5. 2. Hyperresponsiveness to PAF was observed when the lungs were obtained from guinea-pigs used 2 or 7 days after a booster injection of the antigen and, to a lower extent, when they were from animals sensitized by a single antigen administration. By contrast, rhIL-5 did not modify the responses to PAF of lungs from passively sensitized or from adjuvant-treated guinea-pigs, suggesting that immunological stimulation is required to allow the expression of synergism between rhIL-5 and PAF. 3. Guinea-pigs killed 2 and 7 days after the booster injection of the antigen exhibited a marked increase in the number of eosinophils in the bronchoalveolar lavage fluid (BAL), as compared to non-sensitized animals. 4. Our results demonstrate that rhIL-5 and PAF act synergistically to induce enhanced bronchoconstriction and mediator release exclusively when lungs are obtained from guinea-pigs sensitized once to ovalbumin and then boosted. Since recruitment of eosinophils into the airways and the development of hyperresponsiveness to PAF are concomitant, it is suggested that eosinophils are the target cells for interaction between rhIL-5 and PAF.

Inhibition by azelastine of the effects of platelet-activating factor in lungs from actively sensitised guinea-pigs

The effect of azelastine on platelet-activating factor (PAF)-induced bronchoconstriction and mediator release in isolated lungs from actively sensitised guinea-pigs was investigated. Guinea-pigs were actively sensitised with two s.c. injections of 10 micrograms ovalbumin in 1 mg Al (OH)3 at a 2-week interval. One week after the second injection, the lungs were removed and challenged intra-arterially with PAF or arachidonic acid. In some experiments lungs from non-immunised guinea-pigs were injected with PAF or histamine. Bronchoconstriction, the release of thromboxane (TX)B2 or leukotriene (LT)-like material and the histamine content of the effluent were evaluated. Azelastine was given s.c. at 10 or 100 micrograms/kg, 4 h before lung removal. Azelastine (100 micrograms/kg) did not inhibit PAF-induced bronchoconstriction and mediator release from lungs from non-immunised guinea-pigs. In contrast, the hyperresponsiveness to 1 ng PAF observed in lungs from actively sensitised animals was dose dependently inhibited by azelastine. Azelastine did not reduce the histamine-induced bronchoconstriction and consequent TXB2 release from lungs from immunised guinea-pigs, indicating that the protective effect exerted against hyperresponsiveness to PAF was not due to histamine antagonism. Azelastine also reduced arachidonic acid-induced bronchoconstriction and LT-like material release from sensitised lungs, regardless of the presence of indomethacin. These results suggest that inhibition of lung hyperresponsiveness to PAF by azelastine may result from an interference with leukotriene synthesis.

Blockade of thromboxane/endoperoxide receptor-mediated responses in the pulmonary vascular bed of the cat by sulotroban

The effects of sulotroban (BM13.177; SK & F 95587), a thromboxane (TX) A2/endoperoxide (PGH2) receptor blocking agent on responses to the TXA2/PGH2 mimics, U46619 and U44069, were investigated in the pulmonary vascular bed of the intact-chest cat under constant flow conditions. Injections of U46619 and U44069 directly into the perfused lobar artery caused dose-related increases in lobar arterial pressure without altering left atrial pressure. Following administration of sulotroban in a dose of 5 mg/kg i.v., dose-response curves for U46619 and U44069 were shifted to the right in a parallel manner. The duration of the blocking effect of sulotroban was investigated, and responses to U46619 returned to approximately 50% of control in 120 min and were not significantly different from control 240 min after administration of the receptor antagonist. Sulotroban was without significant effect on responses to prostaglandin (PG) D2 or F2 alpha or serotonin, histamine, norepinephrine, angiotensin II or BAY K8644, an agent which enhances calcium entry. Sulotroban was without effect on responses to endothelin (ET)-1, sarafotoxin (S) 6a or S6c and platelet-activating factor (PAF). Sulotroban did not alter baseline vascular pressures in the cat and responses to the PG and TXA2/PGH2 precursor, arachidonic acid, were reduced. The present data show that sulotroban selectively blocks TXA2/PGH2 receptor-mediated responses in a competitive and reversible manner in the pulmonary vascular bed.(ABSTRACT TRUNCATED AT 250 WORDS)

Pertussis toxin induces bronchopulmonary hyperresponsiveness in guinea-pigs while antagonizing the effects of formyl-L-methionyl-L-leucyl-L-phenylalanine

Pertussis toxin injected i.v. at 0.8-20 micrograms/kg markedly enhanced bronchoconstriction induced by the i.v. administration of histamine or serotonin (5-HT) (0.5-16 micrograms/kg) to propranolol-treated guinea-pigs, under conditions where propranolol or pertussis toxin alone were poorly effective. In contrast, bronchoconstriction and the accompanying leukopenia induced by the i.v. administration of the secretagogue formyl-L-methionyl-L-leucyl-L-phenylalanine (fMLP) were suppressed by pertussis toxin. Bronchoconstriction induced by histamine or 5-HT was not enhanced when perfused lungs from pertussis toxin-treated guinea-pigs were studied in vitro, under conditions where bronchoconstriction and thromboxane A2 release evoked by fMLP were suppressed. Pertussis toxin negatively modifies signal transduction in cells involved in the lung responses to fMLP both in vivo and in vitro, but positively and only in vivo it modifies signal transduction in cells involved in the lung responses to the direct constricting agents histamine and 5-HT. As hyperresponsiveness to histamine and 5-HT were exclusively found in vivo, the target for pertussis toxin is probably not the adrenergic nor the cholinergic systems, since neither hexamethonium, isoprenaline, atropine nor vagotomy were effective. In addition, since dexamethasone and nedocromil sodium were inactive and enrichment of bronchoalveolar lavage with inflammatory cells was not noted, despite lung invasion by neutrophils and lymphocytes, acute inflammation does not account for pertussis toxin-induced hyperresponsiveness.

PAF-induced muscarinic cholinoceptor hyperresponsiveness of ferret tracheal smooth muscle and gland secretion in vitro

1. The effects of exposure of the ferret trachea in vitro to platelet activating factor (PAF) were examined on methacholine-induced smooth muscle contraction, mucus volume and lysozyme outputs, and albumin transport across the tracheal epithelium. 2. Methacholine (0.1-30 microM) produced concentration-dependent increases in tracheal smooth muscle tone and mucus volume, lysozyme and albumin outputs from the trachea. 3. The concentration-response curves for methacholine-induced smooth muscle contraction, mucus volume and lysozyme outputs were all shifted upwards after exposure of the trachea to PAF (1 microM) with a significant increase in maximum response for each variable. The EC50 values for methacholine-induced smooth muscle contraction and mucus volume output were significantly reduced after PAF exposure suggesting an increase in the potency of methacholine. The concentration-response curve for methacholine-induced albumin output was shifted downwards after PAF exposure with a greatly reduced maximum but no change in the EC50 for methacholine. 4. PAF-induced hyperresponsiveness of methacholine-induced smooth muscle contraction, mucus volume and lysozyme outputs was not affected by indomethacin, FPL55712, or mepyramine and cimetidine, but was prevented by catalase and superoxide dismutase (SOD), and by WEB2086. Similarly, PAF-induced inhibition of methacholine-stimulated albumin output was prevented by catalase and SOD, and by WEB2086. 5. We conclude that PAF induces hyperresponsiveness of ferret tracheal smooth muscle and submucosal gland secretion (including lysozyme secretion from serous cells) to methacholine. This hyperresponsiveness is probably produced by receptor-mediated release of oxygen free-radicals. The inhibition of methacholine-induced albumin flux suggests a loss of epithelial function which is also probably mediated by release of free-radicals. The mechanism by which the free-radicals produce the changes in responsiveness to methacholine, and the cellular source of the free-radicals, remain to be established.

Protective effect of SR 27417, a novel PAF antagonist, on lethal anaphylactic and endotoxin-induced shock in mice

In anaphylactic shock, SR 27417, the first member of a newly developed series of PAF (platelet-activating factor) antagonists, inhibited in a dose-dependent manner the lethal effect of antigen (ovalbumin) rechallenge in actively sensitized mice. It protected mice when given i.v. 5 min before ovalbumin challenge (ED50 = 50 micrograms/kg) or when given p.o. 1 h before ovalbumin administration (ED50 = 1.25 mg/kg). After i.v. or oral administration, SR 27417 (2.5 and 10 mg/kg, respectively) greatly improved the survival rate of mice after antigen challenge and had an extremely long duration of action (48 and 30 h, respectively). Similarly, i.v. or oral doses of SR 27417 afforded in mice complete protection against endotoxin-induced lethality (ED50 values were 100 and 150 micrograms/kg, respectively). SR 27417 (1 mg/kg) inhibited endotoxin-induced death in mice with impressive oral or i.v. durations of action of 66 and 110 h, respectively. These results confirm that PAF plays a major role in anaphylactic and endotoxin-induced shock and that SR 27417 may be an effective preventative drug.

Inhibitory effects of a novel PAF antagonist E6123 on anaphylactic responses in passively and actively sensitized guinea pigs and passively sensitized mice

The effects of the platelet-activating factor (PAF) antagonist, E6123, on anaphylactic responses in guinea pigs and mice were investigated. E6123 inhibited i.v. antigen (Ag)- or inhaled Ag-induced bronchoconstriction in passively and actively sensitized guinea pigs after oral administration at 3 and 10 micrograms/kg, respectively. E6123 inhibited Ag inhalation-induced airway hyperreactivity in guinea pigs after oral administration at 30 micrograms/kg. E6123 protected mice from anaphylactic death with an ED50 value (p.o.) of 7 micrograms/kg. The inhibitory effects of E6123 described above were very potent compared to those of the PAF-antagonists WEB2347 and Y-24180. The present results suggest that E6123 may be beneficial for the treatment of asthma, a condition in which PAF is assumed to be involved.

Antagonism of platelet-activating factor in isolated rat colon: possible mechanism

The contractions of three different regions of rat colon in response to platelet-activating factor (PAF) were compared. The ascending colon was found to be the most responsive. The slow contraction of the ascending colon induced by PAF was dependent on external Ca2+. CV-3988, a structural analog of PAF, slowly induced irreversible inhibition of PAF-induced contraction, whereas FR-900452, which is structurally unrelated to PAF, caused rapid reversible inhibition of PAF-induced contraction. No inhibitory effects of CV-3988 were observed when the strip was washed with Tyrode's solution containing 1% bovine serum albumin (BSA). The results suggest that PAF and CV-3988 penetrate slowly into the outer half of the lipid bilayer of plasma membranes of cells in isolated rat colon, and then rapidly diffuse laterally to associate firmly with specific binding sites.

Epithelial modulation of thromboxane A2 and PAF involvement in IgE- and IgG-mediated guinea pig anaphylaxis

The role of prostanoids and platelet-activating factor (PAF) was studied in the in vitro response of guinea pig trachea to immunochallenge according to the presence or the absence of the epithelial layer and to the sensitization procedure leading to the preferential synthesis of immunoglobulin E (IgE) or immunoglobulin G (IgG) antibodies. Indomethacin, a cyclooxygenase inhibitor, potentiated the antigen-induced contractions both in IgE and IgG models, suggesting the involvement of relaxant prostaglandins (PGs), independently of the presence of the airway epithelium. UK-38485, a thromboxane synthetase inhibitor, did not modify the tracheal response to antigen in the IgE model. However, this compound enhanced the maximum contractile response to antigen of the intact tracheal strips of IgG-sensitized guinea pig, but reduced the contractile response of the epithelium-free tracheal strips. Two potent non-structurally related PAF antagonists, Ro 19-3704 and BN 52021, reduced antigen-induced contraction of the epithelium-free tracheal strips in the IgE model. In contrast, these compounds did not affect the contractile responses of the preparations in the IgG model. These results suggest the selective implication of thromboxane A2 and PAF, in IgG- and IgE-mediated guinea pig anaphylaxis respectively. Finally, these results indicate that thromboxane A2 (TXA2) and PAF are potent inducers of epithelium-derived mediators.

Effect of azelastine and ketotifen on the bronchial and skin responses to platelet-activating factor in humans

In a randomized, double-blind placebo-controlled study we investigated the effect of single oral doses of 8 mg azelastine and 2 mg ketotifen on the immediate response to platelet-activating factor (PAF) inhalation and to increasing doses of PAF injected intradermally. Bronchial provocation with 100 micrograms of PAF resulted in marked bronchoconstrictor responses, but neither azelastine nor ketotifen had any significant effect on these responses. Intradermal injection of PAF (100, 200 and 400 ng) resulted in a dose-related weal and flare response. Azelastine and ketotifen both caused significant reductions in this response (P less than 0.002-P less than 0.01). There was no significant difference between the effect of the two drugs.

Pharmacological modulation of endothelin-induced contraction of guinea-pig isolated airways and thromboxane release

1. The aim of the present experiments was to study the possible involvement of known bronchoconstrictor substances in mediating the myotropic action of endothelin-1 (ET-1, human-porcine endothelin) in guinea-pig isolated airways. 2. ET-1 (1-100 nM) caused a dose-dependent contraction of guinea-pig trachea, upper bronchus and parenchyma. The contractions developed slowly, reaching maximal values 4-6 min after addition of the peptide. 3. The contractile action of ET-1 was significantly attenuated by indomethacin (10 microM), a cyclo-oxygenase blocker. BM 13505 (5 microM), a thromboxane receptor antagonist, FPL 55712 (19 microM) and YM 16638 (1 microM), antagonists of the sulphidopeptide leukotrienes, BN 52021 (10 microM) and WEB 2086 (1 microM), platelet-activating factor receptor antagonists in all three tissue preparations studied. 4. Pretreatment of the airway tissues with compound U 75302 (3 microM), a selective leukotriene B4 receptor antagonist, or with a mixture of antagonists containing methysergide (0.75 microM), phentolamine (0.4 microM), propranolol (13 microM), atropine (0.4 microM) and diphenhydramine (0.45 microM) did not modify the myotropic action of ET-1. 5. ET-1, 10 and 100 nM induced three, and nine fold increases in thromboxane A2 release from lung parenchymal strips. 6. ET-1-induced thromboxane A2 release was completely abolished by indomethacin, and was significantly attenuated by BN 52021, WEB 2086 and FPL 55712. Neither BM 13505 nor YM 16638 exerted a significant effect on thromboxane release. 7. The present findings show that contraction of guinea-pig airway smooth muscle by ET-1 is mediated, in part, by the release of thromboxane A2, sulphidopeptide leukotrienes and platelet-activating factor, and suggest that the increased thromboxane A2 release following ET-1 is partly a consequence of enhanced synthesis of sulphidopeptide leukotrienes and platelet-activating factor.

Interaction of platelet-activating factor with cultured guinea pig tracheal epithelial cells

The present study has examined the interaction of platelet-activating factor (PAF) with cultured guinea pig tracheal epithelial cells (GTE). PAF stimulated GTE to release endogenous arachidonic acid and metabolize it to prostaglandins E2 and F2 alpha (PGE2 and PGF2 alpha). Prostanoid production by GTE in response to PAF was dose-dependent (0.1-100 nM) and was maximal within 5 min. PGE2 and PGF2 alpha levels increased by 3.3 +/- 0.8 and 3.2 +/- 0.6 ng/10(6) cells respectively over basal levels in response to 100 nM-PAF. The ability of GTE to synthesize and/or catabolize PAF was also examined. GTE readily incorporated [3H]acetate into a product which migrated on t.l.c. with PAF. However, further characterization of this product suggested that label had not been incorporated into PAF, but rather that it was incorporated into another lipid product with chromatographic characteristics similar to those of PAF. In contrast, GTE readily metabolized PAF to inactive products. When [3H]PAF was incubated with GTE, 50% of the total [3H]PAF added was catabolized in approx. 15 min. The major route of catabolism of PAF by GTE was the deacetylation-reacylation pathway, which yielded 1-O-[3H]alkyl-2-acyl-sn-glycerophosphocholine. Determination of the nature of the long-chain acyl group incorporated into the sn-2 position of the newly synthesized products revealed that oleic and linoleic acids were the major fatty acids present. Taken together, these results suggest that respiratory epithelial cells respond to stimulation by PAF with enhanced production of PGE2 and PGF2 alpha, and also have the capacity to modulate inflammatory reactions in the airways by their ability to degrade this potent inflammatory mediator.

PAF-induced bronchial hyperresponsiveness in the rabbit: contribution of platelets and airway smooth muscle

1. Aerosol administration of platelet activating factor (PAF) to normal rabbits induced an enhanced airway responsiveness to inhaled histamine, 6 and 24 h after exposure. Following exposure to bovine serum albumin (BSA) as the carrier molecule for PAF, there was an increase in airway responsiveness to histamine 6 h after challenge, although by 24 h this was not significantly different from the responsiveness of airways to histamine before BSA. 2. PAF-induced bronchial hyperresponsiveness at 24 h was associated with a substantial increase in the number of neutrophils and mononuclear cells and a small, but significant increase in the number of eosinophils in the lungs as assessed by bronchoalveolar lavage. BSA exposure failed to alter the total number of cells in the lungs, although there was a significant increase in the number of neutrophils in the bronchoalveolar lavage fluid. 3. Selective platelet depletion with a guinea-pig anti-rabbit platelet serum inhibited PAF-induced bronchial hyperresponsiveness. In addition, there was an attenuation of PAF-induced airway inflammation in animals rendered thrombocytopenic. 4. The contractile potency to histamine, methacholine and carbachol was similar in intrapulmonary bronchi taken from rabbits exposed to an aerosol of BSA or PAF. Furthermore, the relaxant potency to the non-selective beta-adrenoceptor agonist isoprenaline, was unaltered in PAF-treated rabbits. In contrast, there was a 2.58 fold reduction in the relaxant potency to theophylline in rabbits exposed to PAF compared with rabbits exposed to BSA. 5. These results suggest that in the rabbit, PAF-induced bronchial hyperresponsiveness at 24 h is associated with airways inflammation and is dependent upon platelet activation, but is not related to changes in airway smooth muscle function.

Effect of a thromboxane A2 synthetase inhibitor (OKY-046.HCl) on airway hyperresponsiveness in guinea pigs

We studied the effect of (E)-3-[p-(1H-imidazol-1-ylmethyl)phenyl]-2-propenoic acid hydrochloride monohydrate (OKY-046.HCl), a specific thromboxane (TX) A2 synthetase inhibitor, on airway hyperresponsiveness of guinea pigs. OKY-046.HCl (30-100 mg/kg, intraduodenally (i.d.) or orally (p.o.)) suppressed dose dependently the airway hyperresponsiveness to acetylcholine (ACh) induced by formyl-methionyl-leucyl-phenylalanine (FMLP), platelet activating factor (PAF) and repetitive antigen. OKY-046.HCl (100 mg/kg) also inhibited the increase in TXB2 in bronchoalveolar lavage fluid (BALF) induced by FMLP, PAF and antigen. Aspirin 10 or 30 mg/kg i.d. or p.o.) suppressed the airway hyperresponsiveness induced by FMLP and PAF but not by antigen. Azelastine (10 mg/kg i.d.) was ineffective on PAF- and antigen-induced airway hyperresponsiveness. TXA2 mimetic drugs caused airway hyperresponsiveness that was not inhibited by OKY-046.HCl (30 mg/kg i.v.). Furthermore, OKY-046.HCl showed no effect on propranolol- and physostigmine-induced airway hyperresponsiveness which did not accompany TXB2 generation in BALF. The number of eosinophils in BALF increased after FMLP exposure, an effect which was not inhibited by OKY-046.HCl. These results suggest that OKY-046.HCl inhibits airway hyperresponsiveness by suppressing TXA2 generation. We suggest that OKY-046.HCl will be a new antiasthmatic drug.

The actions of GR32191B, a thromboxane receptor antagonist, on the effects of inhaled PAF on human airways

We investigated acute bronchoconstriction and changes in airway responsiveness to methacholine following the inhalation of platelet activating factor (PAF) in an open study of 12 non-asthmatic subjects. Ventilatory function was monitored using a flow rate at 30% of vital capacity (V30) and airway responsiveness was measured as PD40V30, i.e. the dose of metacholine causing a 40% fall in V30. PAF (3-422 micrograms) resulted in dose-related acute bronchoconstriction in 10 of the 12 subjects. There was no association between the airway responsiveness to PAF and to methacholine. Ten subjects showed some increase in airway responsiveness to methacholine 1 or 3 days following PAF. Overall, these changes were statistically significant (P less than 0.05) but were of small magnitude (geometric mean PD40V30pre-PAF = 457 micrograms; 24 hr after PAF = 259 micrograms; 72 hr after PAF = 258 micrograms) and variable: only seven subjects showing increased airway responsiveness on both day 1 and day 3 after PAF. Six subjects who appeared to show increases in airway responsiveness following PAF were re-studied with the inhaled PAF pre-medicated by either placebo or a specific thromboxane receptor antagonist (GR32191B) in a double-blind fashion. GR32191B did not reduce the acute bronchoconstriction due to PAF. In this part of the study, these six subjects did not show significant increases in airway responsiveness following the placebo pre-medicated PAF challenge and so no effect of the drug on airway responsiveness could be shown.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of prostacyclin on bronchoconstriction and neutropenia induced by inhaled platelet-activating factor in man

We studied the effects of prostacyclin (PGI2) on the airway responses to platelet-activating factor (PAF) in a randomized and crossover study in eight normal subjects. PGI2 or diluent (glycine buffer) was continuously infused on 2 separate days. Two breaths of PAF (21 micrograms) were inhaled three times every 15 minutes and airflow at 30% of vital capacity from partial flow-volume curves (Vp30) was measured. PGI2 (4 ng/kg/min) had no effect on Vp30 or blood pressure, whereas heart rate increased from 70.3 +/- 3.9 to 73.7 +/- 4.0 beats/min (mean +/- SEM; p less than 0.01). Two subjects did not complete the study because of transient hypotension. PGI2 had no effect on PAF-induced bronchoconstriction with maximal decreases in Vp30 of 42.0 +/- 8.0% (p less than 0.01) during PGI2 and 49.8 +/- 14.2% (p less than 0.02) during diluent infusion. Ex vivo platelet aggregation to PAF (10(-9) to 10(-7) mol/L) was significantly inhibited by PGI2. Circulating neutrophils decreased from 4.7 +/- 0.9 x 10(9)/L to 1.5 +/- 0.3 x 10(9)/L (p less than 0.05) 5 minutes after the first PAF inhalation during diluent infusion, whereas there was no significant change with PGI2. Thus, PGI2 does not influence PAF-induced bronchoconstriction in man despite causing marked inhibition of ex vivo PAF-induced platelet aggregation and preventing the fall of neutrophils.

Eosinophil accumulation in pulmonary airways of guinea-pigs induced by exposure to an aerosol of platelet-activating factor: effect of anti-asthma drugs

1. Exposure of guinea-pigs to aerosols of platelet activating factor (PAF) (0.01 to 100 micrograms ml-1) induced a dose-dependent increased incidence of eosinophils in bronchoalveolar lavage fluid (BAL) at 48 h. Total leucocyte numbers and the percentages of lymphocytes and neutrophils were unchanged in BAL fluid. 2. Increased numbers of eosinophils were detected in BAL 1 h after exposure to PAF but eosinophilia was not maximal until 48 h. One week after exposure to PAF, the percentage of eosinophils in BAL was within the normal range. 3. Depletion of circulating platelets or neutrophils by intravenous injection of specific antisera did not modify accumulation of eosinophils in the airway lumen following inhalation of PAF (10 micrograms ml-1). 4. PAF-induced pulmonary airway eosinophil accumulation was inhibited by treatment with SDZ 64-412, a selective PAF-antagonist, whether the compound was administered before, or 30 min after, inhalation of PAF. 5. Pulmonary airway eosinophil accumulation due to inhaled PAF (10 micrograms ml-1) was inhibited by prior treatment with aminophylline, cromoglycate, ketotifen, dexamethasone and AH 21-132. 6. Pulmonary airway eosinophil accumulation due to inhaled PAF (10 micrograms ml-1) was not inhibited by prior treatment with indomethacin, salbutamol or mepyramine.

Doxofylline exerts a prophylactic effect against bronchoconstriction and pleurisy induced by PAF

The effect of doxofylline, a new xanthine drug with a low incidence of side-effects in the central nervous, renal and gastroenteric system, on the actions of PAF-acether on bronchopulmonary functions was studied. Doxofylline inhibited: (1) PAF-induced bronchoconstriction in vitro, and the concomitant generation of TXA2-like activity in perfused guinea-pig lungs; (2) PAF-induced bronchoconstriction in vivo and the concomitant release of TXA2-like activity into the circulation; (3) PAF-acether-induced pleurisy and the liberation of type C4 leukotriene into the rat pleural cavity. The results suggest that doxofylline, like theophylline, is able to counteract the bronchoconstriction induced by PAF-acether and, in addition, displays anti-inflammatory properties. These pharmacological data support the notion that doxofylline exerts a prophylactic effect against the respiratory damage induced by mediators, such as PAF-acether, of lung bronchial hyperreactivity; its mechanism of action is unusual, it has slight antagonistic activity at A1- and A2-adenosine receptors.

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.

Interference of WEB 2086 and BN 52021 with Paf-induced effects on guinea-pig trachea

1. The thienotriazolodiazepine WEB 2086 and the gingkolide BN52021 have been evaluated as antagonists of Paf-acether (Paf) by studying their effects on Paf-induced relaxation and Paf-induced prostaglandin E2 (PGE2) production in histamine-contracted guinea-pig tracheal preparations. 2. Relaxation induced by Paf 4 microM in histamine-contracted guinea-pig tracheal preparations was 39.67 +/- 3.5% (n = 30). At the same concentration, Paf significantly increased PGE2 production from histamine-contracted guinea-pig tracheal preparations. 3. WEB 2086 inhibited in a dose-related manner (IC50 = 21.2 nM) the relaxant effect induced by Paf and, at 1 microM, suppressed Paf-induced release of PGE2. 4. BN 52021 100 microM inhibited to about 60% Paf-induced relaxation of histamine-contracted guinea-pig tracheal preparations, but completely abolished Paf-induced increase in PGE2. 5. Both antagonists had no effects on relaxations induced by arachidonic acid 10 microM or PGE2 0.1-1 microM in histamine-contracted guinea-pig tracheal preparations. 6. The results are consistent with the presence of specific Paf receptors in guinea-pig trachea and indicate that a relaxant prostanoid, namely PGE2, at least partially mediates Paf-induced relaxation in this experimental model.

Pharmacological modulation of the bronchopulmonary action of the vasoactive peptide, endothelin, administered by aerosol in the guinea-pig

Administration by aerosol for 1 min of solutions of endothelin (ENDO; 1, 5 or 10 micrograms/ml) to anaesthetized and ventilated guinea-pigs induced a dose-dependent bronchopulmonary response (BR) which was maximal within 4 to 5 min. In contrast, no significant change of the mean arterial blood pressure was observed. Pretreatment of guinea-pigs with propranolol (1 mg/kg, i.v.), mepyramine (1 mg/kg, i.v.), nifedipine (50 mg/kg, i.p.) or verapamil (0.3 mg/kg, i.v.) did not significantly affect the BR induced by an aerosol of a solution of 10 micrograms/ml ENDO. In contrast, BR was significantly reduced when the animals were pretreated with the cyclooxygenase inhibitor, indomethacin (10 mg/kg, i.v.) or the platelet-activating factor (PAF) receptor antagonist, BN 52021 (10 mg/kg, i.v.). These results indicate that aerosolized ENDO induces a BR via the generation of secondary mediators such as cyclooxygenase products and PAF in a process which is unaffected by the blockers of the voltage-dependent calcium channels.

Release of eicosanoids in rat peritoneal cavity during the Arthus reaction. Effect of the PAF-antagonist BN-52021 and indomethacin

An Arthus reaction was induced in the rat peritoneal cavity. The inflammatory exudates were collected 10 min after induction of the reaction and analysed for the presence of prostaglandin E2 (PGE2) and thromboxane B2 (TXB2) by enzyme immunoassays (EIA), and of leukotriene B4 (LTB4) by radioimmunoassay. Our results showed that control release (CONT) of eicosanoids in the peritoneal cavity averaged 2.3 ng/ml for TXB2, 0.21 ng/ml for PGE2 and 18 pg/ml for LTB4. Following antigen challenge, the levels of TXB2, PGE2 and LTB4 in the peritoneal cavity increased to 17.0 ng/ml, 0.41 ng/ml and 49.0 pg/ml, respectively. Indomethacin totally inhibited the release of PGE2 and TXB2 whereas it increased by 326% the release of LTB4. The PAF antagonist, BN-52021 significantly inhibited (around 40%) the release of LTB4 in rat peritoneal cavity, increased the release of PGE2, and did not affect the release of TXB2. These results clearly suggest a mediatory role for both cyclooxygenase and lipoxygenase products in Arthus reaction and provide evidence that PAF is also involved in complex interactions with the eicosanoids.