Postvagotomy changes in neurogenic plasma extravasation in rat bronchi

The present study was carried out to test if plasma extravasation induced by capsaicin (90 micrograms/kg) in the bronchi of Sprague-Dawley rats could be reduced 10-30 min (0 day), 20-24 h (1 day), 3, 7 or 14 days after unilateral midcervical vagotomy. The second aim of this study was to demonstrate if substance P (3 micrograms/kg) could intensify neurogenic plasma extravasation in the bronchi in which sensory innervation was partially deprived by vagotomy. In the rats 0 days after vagotomy (0 days postvagotomy) that received capsaicin, plasma extravasation in the mainstem and secondary bronchi ipsilateral to vagotomy did not decrease. Capsaicin-evoked plasma extravasation in the secondary bronchi ipsilateral to vagotomy decreased significantly 1, 3, 7 and 14 days after vagotomy as compared with that of 0 days postvagotomy. Differences in extravasation between the secondary bronchi of the two sides were usually significant in animals 3, 7 or 14 days postvagotomy. The effect of unilateral vagotomy on plasma extravasation in the mainstem bronchi was variable. Plasma extravasation produced by substance P in the mainstem and secondary bronchi of rats 0 days postvagotomy was similar to that of unoperated rats receiving either capsaicin or substance P. Unilateral vagotomy did not decrease the amount of substance-P-induced plasma extravasation in the mainstem or secondary bronchi ipsilateral to vagotomy in rat groups 1, 3, 7 or 14 days postvagotomy as compared with that of their contralateral bronchi. This study suggests that the secondary bronchi were the chief location of the bronchial tree that could be desensitized after unilateral cervical vagotomy to stimulation by the irritant capsaicin. This desensitization developed within 1 day after vagotomy, therefore the capsaicin-evoked neurogenic inflammation in the bronchi of the vagotomized side was reduced. Exogenous substance P resulted in mucosal edema and degranulation of goblet cells in the bronchi of both vagotomized and opposite sides. The number of mediator-sensitive blood venules did not decrease following vagotomy operation. It is suggested that substance P was insufficient after vagal denervation, but substance-P receptors on the endothelial cells and goblet cells in the denervated regions were still operative.