Enhancement of Microvascular Leakage in the Nasal Mucosa after Re-exposure to Capsaicin in a Rat Model Challenged/Rechallenged with Capsaicin

ABSTRACT

It has been suggested that the role of neurogenic inflammation is to protect the airway from various noxious irritants in inhaled air. Repeated exposure to various irritating stimuli has become very common in daily life. However, the process that occurs in neurogenic inflammation after repeated exposure to irritating stimuli is not yet clearly understood. The aim of this study was to investigate the changes of microvascular leakage in the airways after re-exposure to capsaicin in an experiment using a rat model challenged/rechallenged with capsaicin. Twenty-four Sprague-Dawley rats were divided into four groups a capsaicin-challenged group (10 microgram/kg of capsaicin, intravenous, n=6) and three capsaicin-rechallenged groups (10 microgram/kg of capsaicin, intravenous, n=6 in each group) corresponding to time intervals of 1, 3, or 6 hours after capsaicin-challenge. The amount of microvascular leakage in the nasal mucosa and trachea of the animal in each group was measured with extravasation of Evans blue dye (30 mg/kg, intravenous) using a spectrophotometer. In the nasal mucosa, a significant enhancement of microvascular leakage with capsaicin-rechallenge was observed at 3 hours after capsaicin-challenge (AVOVAR, * p<0.01). However, there was no significant changes in the trachea. In conclusion, the protective mechanisms against repeated irritating stimuli in the nasal mucosa and trachea are different. After exposure to a noxious irritant, the airway defense mechanism mediated by an axon reflex in the nose may be up- regulated, while that in the trachea may not be changed.