Changes in nasal airway resistance and secretory response in the guinea pig after nasal challenge with capsaicin and histamine.
We studied serial changes of nasal airway resistance (NAR) and secretory response after topical stimulation with either capsaicin or histamine, since both are known to stimulate a chemosensitive sensory C-fiber ending. After topical capsaicin stimulation, a dose-related increase of NAR was noted, with a peak response occurring at 10-20 min. These NAR responses were completely abolished following systemic pretreatment with capsaicin. However, they were not affected by atropine, diphenhydramine or hexamethonium pretreatment. After topical histamine stimulation, an atropine-resistant increase of NAR was found and continued more than 120 min. The early phase of this response was significantly suppressed by the systemic pretreatment with capsaicin. A secretory response also occurred after topical capsaicin stimulation and continued for 30 min. This secretory response was almost completely blocked by atropine, hexamethonium or systemic capsaicin pretreatment and was partially suppressed by diphenhydramine pretreatment. These findings suggest that sensory C-fiber stimulation can induce both atropine-resistant vascular reflexes and atropine-sensitive secretory reflexes, and that these reflexes might play an important role during the early phase after nasal stimulation.