Effects of platelet-activating factor on vascular permeability and granulocyte recruitment in the rat trachea

Effect of azelastine on platelet-activating factor-induced microvascular leakage in rat airways

To determine the effect of the antiallergic drug azelastine on airway mucosal inflammation, we studied airway microvascular permeability in response to platelet-activating factor (PAF) in pathogen-free rats. Vascular permeability and neutrophil accumulation were assessed by the percent area occupied by Monastral blue-labeled blood vessels and by myeloperoxidase-containing granulocytes, respectively, in whole mounts of the trachea and main bronchus. Intravenous PAF caused dose-dependent increases in the area density of Monastral blue-labeled vessels and neutrophil influx, and the former effect was inhibited by depletion of circulating neutrophils by cyclophosphamide or treatment with the neutrophil elastase inhibitor ONO-5046. Pretreatment with azelastine inhibited PAF-induced vascular leakage without affecting neutrophil accumulation. This inhibitory effect of azelastine was not seen in neutropenic rats and ONO-5046-treated rats. PAF increased neutrophil elastase contents in bronchoalveolar lavage fluid, an effect that was inhibited by azelastine. Therefore, azelastine attenuates PAF-induced airway mucosal microvascular leakage, probably involving inhibition of the release of neutrophil elastase from activated neutrophils.

NK1 receptor antagonist CP-99,994 inhibits cigarette smoke-induced neutrophil and eosinophil adhesion in rat tracheal venules

The involvement of neurokinin NK1 receptors in cigarette-induced adhesion of neutrophils and eosinophils to venules of the airway mucosa was investigated. Rats were pretreated with the NK1 receptor antagonist CP-99,994 (4 mg/kg IV), its vehicle, or its inactive enantiomer CP-100,263 before exposure to cigarette smoke. Adherent neutrophils and eosinophils were stained histochemically for endogenous peroxidase activity and were counted in tracheal whole mounts. Plasma leakage was quantified be stereological measurements of the extravasation of Monastral blue. Cigarette smoke induced the adhesion of 104 + 17 neutrophils and 10.4 +/- 1.7 eosinophils per square millimeter of mucosa. CP-99,994 reduced neutrophil and eosinophil adhesion by 66 and 61%, respectively, and reduced plasma extravasation by 61% (p < .05), but CP-100,263 had no significant effect. The inhibitory effects of CP-99,994 appeared to be specific because CP-99,994 had no effect on neutrophil and eosinophil adhesion, or on plasma extravasation induced by platelet activating factor, an inflammatory stimulus acting independently of NK1 receptors. These results suggest that NK1 receptors are involved in cigarette smoke-induced adhesion of neutrophils and eosinophils to the endothelium of venules in the rat tracheal mucosa.

Systemic administration of platelet-activating factor in rat reduces specific pulmonary uptake of circulating monoclonal antibody to angiotensin-converting enzyme

The biodistribution of radiolabeled mouse monoclonal antibody (MoAb) to angiotensin-converting enzyme (ACE) and control, nonimmune mouse IgG in platelet activating factor (PAF)-treated rats was studied. The blood level of both preparations was slightly decreased (90% of the control) in PAF-treated rats. Specific pulmonary accumulation of anti-ACE MoAb was reduced to 50% of control in contrast to a doubling in nonspecific pulmonary uptake of non-immune IgG. The changes in anti-ACE MoAb biodistribution were lung-specific and were accompanied by decrease in the pulmonary ACE activity (to 60% of control) and increase in serum ACE activity (to 170% of control). Thus anti-ACE MoAb reveals PAF-induced changes in the status of the pulmonary ACE and therefore can be used for the studies of pathology of the pulmonary endothelium.

Mechanism of platelet activating factor-induced vascular leakage in the rat trachea

Platelet activating factor (PAF) is a phospholipid mediator of inflammation and vascular leakage that may be important in the etiology of asthma. We and others have demonstrated that PAF causes vascular leakage in the rat trachea. In the present study, we attempted to determine how PAF mediates this effect. Vascular leakage was quantitated by measuring the amount of intravascular Evans blue dye extravasated into tracheal tissue. Intravenously administered PAF increased vascular leakage, although Lyso-PAF and Enantio-PAF had no effect. PAF-induced vascular leakage was inhibited in a dose-dependent fashion by the PAF receptor blocker WEB 2086. However, PAF-induced vascular leakage was not inhibited by blockade of cyclooxygenase/lipoxygenase, calmodulin, calcium channels, protein kinase C, histamine receptors, or by destruction of peptidergic sensory nerves. We conclude that PAF causes vascular leakage in the rat trachea by a stereospecific receptor-mediated mechanism that does not depend on arachidonic acid metabolites, calcium, protein kinase C, histamine, or peptidergic sensory nerves.