Neurogenic inflammation in the rat trachea. I. Changes in venules, leucocytes and epithelial cells.

This study was done to characterize the morphological changes in the respiratory mucosa that occur in neurogenic inflammation, which is a type of inflammation mediated by substances released from sensory nerves. Neurogenic inflammation was produced in the trachea and bronchi of atropine-treated Long-Evans rats by electrically stimulating the left or right superior laryngeal and vagus nerves. This procedure is known to increase vascular permeability in the airways, presumably as a consequence of antidromic activation of sensory vagal axons (Lundberg & Saria, 1982). By using a particulate tracer (Monastral blue, 30 mg kg-1 i.v.) that does not cross the walls of normal tracheal blood vessels but does cross the endothelium of abnormally permeable vessels, it was possible to identify which blood vessels were affected in neurogenic inflammation. Light and electron microscopic examination of tracheas prepared after 2 or 5 min of vagal stimulation revealed that postcapillary venules and collecting venules 7-80 micron in diameter were labelled by extravasated Monastral blue but capillaries, arterioles, and larger venules were not. Venules from which the extravasation occurred had gaps as wide as 1.5 micron between endothelial cells. Most of the abnormally permeable venules were located just beneath the airway epithelium in regions between the cartilaginous rings. Extravasation also occurred from venules in the mucosa overlying the posterior membrane of the extrathoracic trachea, but little occurred in the posterior membrane of the intrathoracic trachea. After unilateral vagal stimulation, vascular permeability was increased on both sides of the trachea; it was also increased in first through fourth order bronchi but only on the side of stimulation. Leucocytes (principally monocytes and neutrophils) were adherent to the endothelium of some of the abnormally permeable venules. Erythrocytes and platelets also were adherent to the walls of some venules. These changes in venules were accompanied by a degranulation of epithelial secretory cells, widening of the spaces between tracheal epithelial cells, and probably an increase in epithelial permeability. Neurogenic inflammation in the trachea and bronchi of rats is thus characterized by increased permeability of postcapillary venules and collecting venules in specific regions of the respiratory mucosa as well as adherence of leucocytes, erythrocytes and platelets to the endothelium of these venules and prominent changes in the respiratory epithelium.