Stimulation of vagal pulmonary C fibers by inhaled wood smoke in rats

This study investigated the stimulation of vagal pulmonary C fibers (PCs) by wood smoke. We recorded impulses from PCs in 58 anesthetized, open-chest, and artificially ventilated rats and delivered 6 ml of wood smoke into the lungs. Within 1 or 2 s after the smoke delivery, an intense and nonphasic burst of discharge [Delta = +7.4 +/- 0.7 (SE) impulses/s, n = 68] was evolved in 60 of the 68 PCs studied and lasted for 4-8 s. This immediate stimulation was usually followed by a delayed and more sustained increase in C-fiber activity (Delta = +2.0 +/- 0.4 impulses/s). The overall stimulation was not influenced by removal of smoke particulates (n = 15) or by pretreatment with vehicle (n = 8) for dimethylthiourea (DMTU; a hydroxyl radical scavenger) or indomethacin (Indo; a cyclooxygenase inhibitor). The immediate-phase stimulation was not affected by pretreatment with Indo (n = 8) but was largely attenuated by pretreatment with DMTU (n = 12) or by a combined treatment with DMTU and Indo (DMTU+Indo; n = 8). Conversely, the delayed-phase stimulation was partially suppressed either by DMTU or by Indo but was totally abolished by DMTU+Indo. These results suggest that 1) the stimulation of PCs is linked to the gas phase of wood smoke and 2) hydroxyl radical, but not cyclooxygenase products, is involved in the immediate-phase stimulation, whereas both metabolites are responsible for evoking the delayed-phase stimulation.