Leakage of macromolecules from guinea-pig tracheobronchial microcirculation. Effects of allergen, leukotrienes, tachykinins, and anti-asthma drugs

Effect of antiasthma drugs on microvascular leakage in guinea pig airways

We have studied the effect of intravenous epinephrine, albuterol, verapamil, and aminophylline on airway microvascular leakage in guinea pigs. Microvascular leakage was induced by platelet-activating factor (PAF; 50 ng/kg intravenously), which acts directly on venular endothelial cells, and measured by quantifying extravasation of Evans blue (EB) dye. Epinephrine (20 micrograms/kg) inhibited PAF-induced changes in dye leakage in larynx and main bronchi; at 80 and 160 micrograms/kg, significant inhibition was observed in all airways studied. This effect was reversed by phentolamine (2.5 mg/kg) or prazosin (100 micrograms/kg). By contrast, albuterol (20 to 320 micrograms/kg) and aminophylline (12.5 to 50 mg/kg) failed to inhibit dye leakage at any dose studied. Verapamil inhibited PAF-increased leakage in larynx, main bronchi, and intrapulmonary airways at the lowest dose tested (125 micrograms/kg), although inhibition was not dose dependent. These results suggest that the antiedema effect of epinephrine may be due to vasoconstriction rather than to a direct effect on endothelial cell contractility and that neither beta-agonists nor theophylline have an inhibitory effect. The inhibitory effect of epinephrine on airway microvascular leakage may have therapeutic implications for asthma.

Changes in epithelial secretory cells and potentiation of neurogenic inflammation in the trachea of rats with respiratory tract infections

In rats respiratory tract infections due to Sendai virus and coronavirus usually are transient, but they can have long-lasting consequences when accompanied by Mycoplasma pulmonis infections. Morphological alterations in the tracheal epithelium and a potentiation of the inflammatory response evoked by sensory nerve stimulation ("neurogenic inflammation") are evident nine weeks after the infections begin, but the extent to which these changes are present at earlier times is not known. In the present study we characterized these abnormalities in the epithelium and determined the extent to which they are present 3 and 6 weeks after the infections begin. We also determined the magnitude of the potentiation of neurogenic inflammation at these times, whether the potentiation can be reversed by glucocorticoids, and whether a proliferation of blood vessels contributes to the abnormally large amount of plasma extravasation associated with this potentiation. To this end, we studied Long-Evans rats that acquired these viral and mycoplasmal infections from other rats. We found that the tracheal epithelium of the infected rats had ten times as many Alcian blue-PAS positive mucous cells as did that of pathogen-free rats; but it contained none of the serous cells typical of pathogen-free rats, so the total number of secretory cells was not increased. In addition, the epithelium of the infected rats had three times the number of ciliated cells and had only a third of the number of globule leukocytes. In response to an injection of capsaicin (150 micrograms/kg i.v.), the tracheas of the infected rats developed an abnormally large amount of extravasation of two tracers, Evans blue dye and Monastral blue pigment, and had an abnormally large number of Monastral blue-labeled venules, particularly in regions of mucosa overlying the cartilaginous rings. This abnormally large amount of extravasation was blocked by dexamethasone (1 mg/day i.p. for 5 days). We conclude that M. pulmonis infections, exacerbated at the outset by viral infections, result within three weeks in the transformation of epithelial serous cells into mucous cells, the proliferation of ciliated cells, and the depletion of globule leukocytes. They also cause a proliferation of mediator-sensitive blood vessels in the airway mucosa, which is likely to contribute to the potentiation of neurogenic inflammation that accompanies these infections.

Inflammatory passage of plasma macromolecules into airway wall and lumen

Anaesthetised guinea-pigs received tracer macromolecules 70-340 kDa intravenously and their erythrocytes were labelled in vivo with 99mTc. Superfusion of tracheal mucosa (via oral catheter) with control solutions and inflammatory agents, was followed by sampling of tracheal surface liquids and tracheal tissue. Under baseline conditions no 125I-fibrinogen (340 kDa) and minimal amounts of erythrocytes, 131I-albumin (70 kDa), and FITC-D (150 kDa) were found in tracheal lavage fluids. Undisturbed baseline conditions with negligible leakage of plasma into airway tissue and lumen were thus obtained with the present provocation and sampling techniques. Superfusion during 2 min with bradykinin 2-10 nmol, histamine 2-8 nmol, capsaicin 0.1-0.4 nmol, PAF 4-8 nmol, ovalbumin 3-6 pmol (in sensitised animals) produced, within 1-10 min, a significant and dose-dependent accumulation of plasma in tracheal tissue and lavage fluids. PAF also induced a late phase plasma leakage response at 5 h. At 10 min PAF given intra-arterially produced a similar leakage into the tissue but less into the lumen compared to topical PAF. Intravenous PAF produced additional effects such as pulmonary oedema. Carbachol 8-16 nmol had only minimal effects on 'leakage' but produced severe bronchoconstriction. Toluene diisocyanate (0.003-0.03 microliter) produced dose-dependent and very sustained (17 h) plasma leakage. Recovery of plasma tracers in airway tissue and surface liquids, respectively, was significantly correlated. As examined with capsaicin, absorption of luminal macromolecules increased only slightly during the exudation process. It is suggested that the consistent inflammatory stimulus-induced passage of plasma into the lumen is a consequence of a load on the basal side of the epithelium induced by the extravasated plasma and its derived peptides. An increased interstitial pressure may transiently separate many epithelial cells allowing a mainly uni-directional almost unrestricted flow of large solutes into the lumen.

Neurogenic inflammation in the rat trachea. II. Identity and distribution of nerves mediating the increase in vascular permeability

This study addresses the question of whether increased vascular permeability, which is a prominent feature of neurogenic inflammation in the respiratory tract, is mediated by sensory axons that end near venules in the airway mucosa. In these experiments, neurogenic inflammation was produced in the tracheal and bronchial mucosa of atropine-treated Long-Evans rats by electrical stimulation of the left or right superior laryngeal nerve and/or cervical vagus nerve. The particulate tracer Monastral blue was injected intravenously to localize the sites of increased vascular permeability, and microspectrophotometry was used to measure the amount of extravasated Monastral blue in the trachea and thereby quantify the increase in vascular permeability. In some rats, selective denervations were made to locate the cell bodies of neurons that mediate the increase in vascular permeability; in others, fluorescence immunohistochemistry and quantitative electron microscopic methods were used to determine which structures in the tracheal mucosa are innervated by these neurons. The study revealed that the vagally mediated increase in vascular permeability was sudden, transient (half-life = 2.4 min) and restricted to venules. Stimulation of the left or right superior laryngeal nerve increased the permeability of venules in the extrathoracic trachea, whereas stimulation of either vagus nerve increased vascular permeability in the intrathoracic trachea and bronchi. All nerves had bilateral effects in the trachea, but the vagus nerves had largely unilateral effects in the bronchi. Neurons that mediated the increase in venular permeability had their cells bodies in the jugular (superior sensory) ganglion of the vagus nerve or rostral portion of the nodose (inferior sensory) ganglion. Preganglionic autonomic vagal neurons in the brain stem were not essential for this increase in venular permeability. Few nerves identifiable by substance P-immunohistochemistry or electron microscopy were located near the affected venules, and no nerves were within 1 micron of the walls of venules. However, the epithelium and arterioles of the airway mucosa were densely innervated. All intraepithelial nerves were within 0.1 micron of epithelial cells, and at least two-thirds of nerves near arterioles were within 1 micron of the vessel walls. We conclude that the increase in venular permeability associated with neurogenic inflammation in the trachea and bronchi of rats is mediated by sensory axons that travel in the vagus nerves and superior laryngeal nerves.(ABSTRACT TRUNCATED AT 400 WORDS)

Plasma exudation and asthma

Several pieces of evidence support the view that exudation of plasma into the airway wall and into the airway lumen occurs in asthma. Vascular leakage of plasma results from inflammatory mediator-induced separation of endothelial cells in postcapillary venules belonging to the tracheobronchial circulation. Whereas proposed mediators of asthma induce reversible leakage, several antiasthma drugs exhibit antileakage effects in animals and humans. Potential consequences of plasma exudation are many. Mucosal/submucosal edema might contribute to airway hyperresponsiveness. Plasma exudate in the airway lumen in asthma may contribute to sloughing of epithelium, impairment of mucociliary transport, narrowing of small airways, and mucus plug formation. Exuded plasma may cause airway inflammation and constriction because of its content of powerful mediators, and chemoattractant factors and plasma proteins may condition the inflammatory cells abundant in asthmatic airways to release mediators in response to stimuli that otherwise would be innocuous to the cells. It is concluded that inflammatory stimulus-induced increase in macromolecular permeability of the tracheobronchial microvasculature and mucosa may be a significant pathogenetic mechanism in asthma and that the postcapillary venular endothelium and airway epithelium that regulate leakage of plasma are important effector cells in this disease.

Blockade by theophylline of capsaicin-induced motor effects in guinea-pig airways

The effect of theophylline was tested on the capsaicin-induced increase in insufflation pressure in anaesthetized guinea-pigs and contraction of isolated tracheal spirals. Theophylline (6.25-25 mg/kg i.v.) inhibited in a marked, prolonged and dose-related manner the increase in insufflation pressure elicited by i.v. injection of capsaicin (2-10 micrograms/kg). Theophylline, even at plasma concentrations as low as 15-23 micrograms/ml (which are within or slightly higher than the therapeutic range in humans) produced an inhibition of about 30-50% of capsaicin-induced bronchospasm. Theophylline was significantly less effective in antagonizing the bronchospasm elicited by maximally effective dose (100 micrograms/kg i.v.) of acetylcholine as well as by a dose equieffective to capsaicin 10 micrograms/kg (i.e. acetylcholine 50 micrograms/kg). Theophylline (30 microM-1 mM) also inhibited potently and concentration dependently the capsaicin-induced contraction in vitro and, again, it was significantly less effective against cholinomimetic-induced responses. These data suggest that theophylline can interfere, at therapeutic doses, with some process(es) selectively involved in capsaicin-induced neuropeptide-mediated bronchoconstriction. Since capsaicin-sensitive sensory fibers are thought to be involved in the pathogenesis of bronchial hyperreactivity and asthma, these inhibitory actions of theophylline might be relevant for its therapeutic effects.