Effect of olvanil on the afferent and efferent function of capsaicin-sensitive C-fibers in guinea pig airways

The aim of the present study was to examine the ability of the nonpungent vanilloid VR1 receptor agonist, olvanil, to activate the afferent and efferent function of capsaicin-sensitive C-fibers in guinea pig airways. We found that while capsaicin (10 nM-10 microM) and resiniferatoxin (0.1 nM-1.0 microM) evoked a robust contraction of the guinea pig trachea in vitro, olvanil (10 nM-10 microM) was a weak spasmogen. In addition, pretreatment with olvanil caused only a minor reduction of subsequent responses to capsaicin or resiniferatoxin. Using single fiber recording from guinea pig airway C-fibers, we found that olvanil (10 microM) did not evoke action potential discharge although these fibers responded vigorously to capsaicin after prolonged treatment with olvanil (10 microM). These findings are indicative of significant differences in the relative sensitivity of vanilloid VR1 receptor-transfected cells and the peripheral terminals of airway C-fibers to pungent and nonpungent vanilloid VR1 receptor agonists.