Vincent Lagente

Desensitization to PAF-induced bronchoconstriction and to activation of alveolar macrophages by repeated inhalations of PAF in the guinea pig.

Guinea-pig alveolar macrophages are activated in the presence of PAF-acether (PAF), as shown by O2.- production, suggesting that these cells, abundant in the lungs, are involved in PAF-induced bronchoconstriction. Alveolar macrophages collected after in vivo desensitization to the bronchoconstrictor effect of PAF became refractory to it in vitro, whereas the O2.- production in response to f-met-leu-phe persisted, although it was diminished suggesting a partial cross-desensitization. A similar desensitization to PAF was also observed in alveolar macrophages in vitro, demonstrating a stimulus-specific process. This study suggests that alveolar macrophages may be involved in bronchoconstriction induced by aerosol of PAF.

Interference of BN 52021 (ginkgolide B) with the bronchopulmonary effects of PAF-acether in the guinea-pig

The interaction between the ginkgolide BN 52021 and the effects of PAF-acether on the bronchopulmonary system of the guinea-pig was studied. In pentobarbitone or ethyl carbamate-anaesthetized animals, BN 52021 (1 mg/kg i.v. or 10 mg/kg p.o.) inhibited bronchoconstriction, the hematocrit increase and the accompanying thrombopenia and leukopenia induced by PAF-acether (33-100 ng/kg) and failed to block the bronchoconstriction produced by collagen, arachidonic acid and the tripeptide formyl-Met-Leu-Phe (FMLP). BN 52021, 3 mg/kg, reduced the bronchoconstriction induced by aerosolized PAF-acether. BN 52021, 300 microM, also inhibited the superoxide production by PAF-acether-stimulated alveolar macrophages and failed to reduce the same effects when triggered by FMLP (0.01-1 microM). BN 52021 blocked the formation of thromboxane-triggered by PAF-acether (100 ng) injected into perfused lung, under conditions where the effects of arachidonic acid where not modified. Finally, pretreatment of parenchyma lung strips with BN 52021 (100 microM) partially inhibited the contraction induced by PAF-acether (0.1 microM) and suppressed the accompanying release of thromboxane. BN 52021 is a selective antagonist of the effects of PAF-acether on the bronchopulmonary system and on circulating blood cells of the guinea-pig.

Interference of the PAF-acether antagonist BN 52021 with passive anaphylaxis in the guinea-pig

PAF-acether may be involved in anaphylaxis and asthma. We tested the new PAF-acether antagonist BN 52021 against the effects of antigen in passively sensitized guinea-pigs. Bronchoconstriction by ovalbumin administered i.v. (1 mg/kg) or by aerosol (1 or 10 mg/ml for a period of 1 min) was significantly reduced by BN 52021 (1-10 mg/kg), which did not inhibit drop of leukocyte counts after the i.v. challenge. In both cases, when the guinea-pigs were pretreated by propranolol, high amounts of BN 52021 became ineffective against shock. The reduction of the anaphylactic bronchoconstriction, induced by the combination of mepyramine, aspirin and FPL 55712 was not improved by BN 52021. Tested on isolated lung strips from passively sensitized guinea-pig, BN 52021, at a concentration which inhibits PAF-induced contraction (0.1 mM), did not inhibit the anaphylactic contraction triggered by the administration of ovalbumin (10 micrograms/ml) nor the accompanying release of histamine and thromboxane. In contrast, BN 52021 (30 microM) significantly reduced the anaphylactic release of histamine and of thromboxane from perfused lungs of passively sensitized guinea-pigs. The results with the isolated lung strips and the propranolol-treated guinea-pigs in vivo suggest a dissociation between the anti-anaphylactic and the anti-PAF-acether properties of BN 52021.

Interference of the Paf antagonist Ro 19–3704 with Paf and antigen‐induced bronchoconstriction in the guinea‐pig

1 In vitro, Ro 19–3704, a structurally related antagonist of platelet‐activating factor (Paf) inhibited selectively rabbit platelet aggregation. In vivo, administered intravenously, it inhibited bronchoconstriction, leukopenia, thrombocytopenia and the accompanying accumulation of platelet aggregates in guinea‐pig lung microvessels induced by i.v. Paf. Administered by aerosol, Ro 19–3704 failed to inhibit bronchoconstriction, thrombocytopenia or leukopenia due to i.v. Paf. 2 Bronchoconstriction induced by Paf, in aerosol form, was blocked by Ro 19–3704 administered by the i.v. or aerosol route, which suggests that it interacts with pulmonary cells responsible for bronchoconstriction. 3 Ro 19–3704 has free radical scavenging properties, since it inhibited the production of superoxide anions by macrophages stimulated by Paf and by N‐formyl‐methionyl‐leucyl‐phenylalanine (FMLP). Ro 18–7715, another Paf antagonist and analogue of Ro 19–3704, failed to inhibit the production of superoxide anions by macrophages stimulated by FMLP at concentrations which were effective against Paf. 4 Administered intravenously, Ro 19–3704 failed to block bronchoconstriction induced by an i.v. injection of ovalbumin to guinea‐pigs passively sensitized with anti‐ovalbumin antiserum. Passive pulmonary anaphylaxis due to an aerosol of ovalbumin was blocked by i.v. Ro 19–3704.

Pharmacological control of the in vivo passive anaphylactic shock by the PAF-acether antagonist compound BN 52021

BN 52021 antagonized PAF-acether-induced bronchoconstriction (BC) in the guinea-pig and inhibited BC triggered by antigen in passively sensitized animals. The anti-anaphylactic activity was prevented by propranolol and may either result from an additional property of the drug, independent from PAF antagonism or from different PAF-dependent mechanisms with different responsiveness to the various antagonists.

Pharmacological modulation of the effects of N‐formyl‐L‐methionyl‐L‐leucyl‐L‐phenylalanine in guinea‐pigs: involvement of the arachidonic acid cascade

1 The intravenous administration of the chemotactic and secretagogue peptide N‐formyl‐L‐methionyl‐L‐leucyl‐L‐phenylalanine (FMLP; 0.3–30 μg kg−1) to the guinea‐pig induces bronchoconstriction and dose‐dependent leukopenia accompanied by mild thrombocytopenia. No electron microscopic evidence of platelet aggregation in lungs or significant accumulation of 111In‐labelled platelets in the thoracic region at the height of bronchoconstriction was noted. 2 Bronchoconstriction and leukopenia induced by FMLP were not affected by prostacyclin, by platelet depletion, by the platelet‐activating factor (Paf‐acether) antagonist BN 52021 or by the histamine H1‐antagonist mepyramine. Bronchoconstriction, but not leukopenia, was inhibited by aspirin, whereas the peptido‐leukotriene antagonist compound FPL 55712 and the cyclo‐oxygenase lipoxygenase inhibitor indomethacin reduced bronchoconstriction to a limited extent only. The mixed cyclo‐oxygenase/lipoxygenase inhibitor compound BW 755C was very effective in blocking bronchoconstriction by the highest dose of FMLP used, but failed to interfere with leukopenia. 3 FMLP‐induced dose‐dependent contraction of parenchymal lung strips was accompanied by the formation of immuno‐reactive thromboxane B2 in amounts markedly less than those formed from exogenous arachidonic acid at concentrations equieffective in inducing contractions. 4 FMLP‐induced contractions of the guinea‐pig lung strip were not modified by mepyramine nor by FPL 55712. They were reduced by indomethacin and aspirin and an even greater reduction was obtained with aspirin used in combination with FPL 55712. BW 755C suppressed the effects of all the concentrations of FMLP tested, whereas tert‐butyloxy‐carbonyl‐L‐methionyl‐L‐leucyl‐L‐phenylalanine, a chemical analogue of FMLP, displaced the concentration‐response curve to the right, without reducing the maximal contraction obtained. 5 The present results indicate that: (a) bronchoconstriction by FMLP is not due to platelet activation, to cyclo‐oxygenase‐dependent mechanisms or to peptido‐leukotriene formation. The inhibitory effect of aspirin and BW 755C involves a property other than cyclo‐oxygenase inhibition, which is not shared by indomethacin. (b) The contractile effects of FMLP on parenchymal lung strips follow an interaction with specific receptor sites, as shown by the effectiveness of tert‐butyloxy‐carbonyl‐L‐methionyl‐L‐leucyl‐L‐phenylalanine, and involves the combined effects of cyclo‐oxygenase and lipoxygenase metabolites.

A study with BN 52021 demonstrates the involvement of PAF-acether in IgE-dependent anaphylactic bronchoconstriction

The involvement of platelet activating factor (PAF) in anaphylaxis was examined by recording the pulmonary responses of anesthetized passively sensitized guinea-pigs to the aerosolization of ovalbumin. Animals were tested with and without BN 52021 (a ginkgolide B, PAF receptor antagonist) pretreatment. Aerosolization of ovalbumin produced a bronchoconstriction (BC) which could be made refractory to additional challenges with the antigen. In animals desensitized to ovalbumin, aerosolization of PAF produced an unattenuated BC. Guinea pigs desensitized by repeated aerosolizations of PAF subsequently showed reduced responses to aerosolized antigen suggesting that PAF may be involved in the BC. Animals pretreated with BN 52021, were protected against the effects of systemically administered PAF and also showed reduced responses to aerosolized antigen. Aerosolization of the leukotriene antagonist, FPL 55712, was ineffective against anaphylactic BC under conditions where catecholamine and histamine release were blocked.

Pharmacological modulation of the respiratory and haematological changes accompanying active anaphylaxis in the guinea-pig.

The intrathoracic accumulation of radiolabelled platelets was recorded in anaesthesized, sensitized guinea-pigs concomitantly with changes in airways resistance during active anaphylaxis. Antigen challenge induced an increased airway resistance associated with intrathoracic platelet accumulation, thrombocytopenia and leukopenia. Bronchoconstriction, but not the haematological changes, was modified by a combination of mepyramine, methysergide and aspirin. The addition of FPL 55712 and PGI2 to this cocktail of drugs additionally inhibited the thrombocytopenia and leukopenia but not the intrathoracic accumulation of platelets induced by antigen challenge. PGI2 was alone able to significantly inhibit the intrathoracic platelet accumulation, but not the bronchoconstriction induced by antigen challenge. These results suggest that active anaphylaxis is associated with activation of blood elements and subsequent pulmonary entrapment of platelets but that the platelet release reaction rather than the embolisation of platelet aggregates is the critical step in the induction of allergic bronchoconstriction in the guinea-pig.

Pulmonary anti-anaphylactic activity of clenbuterol tested on actively and passively sensitized guinea-pigs.

Clenbuterol, an adrenergic beta-mimetic agent free of cardiostimulant effects, prevents the release of histamine from isolated rat mast cells. We studied its anti-anaphylactic activity in guinea-pigs and compared it with that of isoprenaline. At doses inactive against the bronchoconstriction caused by 5HT, clenbuterol (3 micrograms/kg) and isoprenaline (0.1-0.3 micrograms/kg) prevented the bronchoconstriction due to 1 mg/kg ovalbumin infused into passively sensitized animals. Clenbuterol and isoprenaline (0.5-1 microM) inhibited by 40% the contractions of superfused parenchyma lung strips from actively sensitized animals, stimulated with 0.3, 1 and 10 micrograms of ovalbumin. When strips from passively sensitized animals were challenged in the organ bath, clenbuterol and isoprenaline (0.01 microM) reduced by 50% the contraction triggered by 10 micrograms/ml of ovalbumin. These concentrations of clenbuterol were ineffective against contractions caused by acetylcholine. Clenbuterol and isoprenaline (0.001-0.01 microM) inhibited the release of histamine and of thromboxane A2 triggered by ovalbumin (0.1, 1 and 10 micrograms) injected into isolated lungs from actively sensitized guinea-pigs indicating that the anti-anaphylactic properties of clenbuterol are independent from its smooth muscle relaxing activity.

Involvement of PAF-Acether in Anaphylactic Bronchoconstriction Induced in Guinea Pigs by Aerosolized Antigen

Bronchoconstriction following the aerosolization of PAF-acether or antigen to guinea pigs induces autodesensitization, but the responses to direct spasmogenic substances are not modified. Bronchoconstriction by PAF-acether is not reduced when it is aerosolized to passively sensitized animals previously desensitized by repeated inhalations of the allergen (ovalbumin). In contrast, when passively sensitized animals are initially desensitized to PAF-acether by repeated inhalations of this agonist, ovalbumin aerosolization induces a bronchoconstriction which is significantly reduced when compared with the response obtained in nondesensitized animals though, in this case, the response to aerosolized histamine is not modified. Thus, PAF-acether is released during intrapulmonary anaphylactic shock induced by aerosolized ovalbumin and can be a prime candidate for its development.