Local and systemic capsaicin pretreatment inhibits sneezing and the increase in nasal vascular permeability induced by certain chemical irritants.

The effects of local exposure to chemical irritants and mechanical stimulation on sneezing reflexes have been studied in normal and capsaicin-pretreated, conscious guinea-pigs. The influence of local and systemic capsaicin pretreatment on vascular permeability to plasma proteins and the cardiovascular effects of local application of capsaicin to the nasal mucosa have also been studied in anaesthetized animals. Local application of capsaicin (threshold dose 3 microM), nicotine (threshold dose 300 microM) or formalin to the nasal mucosa induced reflex sneezing discharges. Systemic or local capsaicin pretreatment abolished or reduced the sneezing responses to capsaicin and formalin. The response to nicotine was also reduced following local pretreatment with capsaicin, while the response to systemic pretreatment with capsaicin was only slightly affected. The sneezing response to mechanical stimulation was not affected by capsaicin pretreatment. Pretreatment with a local anaesthetic induced a similar dose-dependent inhibition of the sneezing responses to both capsaicin and nicotine. Local application of disodium cromoglycate to the nasal mucosa reduced the sneezing response to capsaicin, but not that to nicotine. Local pretreatment with the 3 mM and 30 mM capsaicin solution inhibited the increase in vascular permeability to plasma proteins in the nasal mucosa induced by i.v. capsaicin. Local pretreatment with capsaicin did not result in any reduction in the capsaicin-induced permeability in the ureter, suggesting that such treatment did not have any major systemic toxic effects. However, a small, acute increase in respiratory insufflation pressure, indicating broncho constriction, was seen when the 30 mM capsaicin solution was applied to the nasal mucosa.(ABSTRACT TRUNCATED AT 250 WORDS)