Fig. 4

Reduction of capsaicin-induced contraction in guinea pig tracheal rings. Tracheal rings were pretreated with 1–100 μM dexmedetomidine, 0.1–10 μM remifentanil, 10–1000 μM lidocaine, 200 μM bupivacaine or 1 μM tetrodotoxin for 20 min before contraction with 10 μM capsaicin. Dexmedetomidine at 100 μM significantly reduced this contraction (a) but remifentanil had no effect (b). Local anesthetics lidocaine and bupivacaine (Bupi) attenuated this C-fiber mediated contraction, which are mediated by tetrodotoxin (TTX) –resistant sodium channels. Mean ± SEM (n = 6). *p < 0.05, **p < 0.01