Ruthenium red antagonism of capsaicin-induced vascular changes in the rat nasal mucosa

Mechanisms of capsaicin-induced vascular changes were examined in the nasal mucosa of anesthetized adult rats. Intra-arterial infusions of capsaicin at doses of 20–100 pmol/min into the external carotid artery resulted in a dose-dependent increase in nasal blood flow as assessed by laser-Doppler flowmetry. Intra-arterial infusion of ruthenium red (RR, 2.5–10 µmol) prior to the administration of capsaicin significantly inhibited the capsaicin-evoked response. The technique of vascular labelling was used to examine nasal mucosal vascular permeability. Intravenous administration of colloidal silver solution prior to capsaicin infusion resulted in accumulation of colloid in the walls of small blood vessels, indicative of enhanced vascular permeability. Vascular labelling was largely abolished after RR pretreatment. These findings suggest that neuropeptides released from trigeminal sensory nerve endings play a significant role in the local vascular and inflammatory reactions of the nasal mucosa. The experimental approach utilized in this study provides a promising model for defining the roles of capsaicin-sensitive afferent nerves in the mechanisms of allergic and/or inflammatory diseases affecting the nasal mucosa.