STIMULATION OF PULMONARY RAPIDLY ADAPTING RECEPTORS BY INHALED WOOD SMOKE IN RATS

1. The stimulation of pulmonary rapidly adapting receptors (RARs) by w ood smoke was investigated. Impulses from seventy RARs were recorded i n fifty-nine anaesthetized, open chest and artificially ventilated rat s; responses to delivery of 6 mi of wood smoke into the lungs were stu died in sixty-one receptors whereas responses to histamine (10 or 100 mu g kg(-1), I.V.) were studied in the other nine. 2. Delivery of wood smoke stimulated fifty-two of the sixty-one RARs studied. When stimul ated, an intense burst of discharge was evoked within 1 or 2 s of smok e delivery This increased activity quickly peaked in 1-3 s (Delta = 15 .8 +/- 1.6 impulses s(-1); n = 61; mean +/- S.E.M), then declined and yet remained at a level higher than the baseline activity. The mean du ration of the stimulation was 25.1 +/- 2.7 s. In contrast, smoke deliv ery did not affect tracheal pressure. 3. Peak responses of RARs to woo d smoke were partially reduced by removal of smoke particulates and we re largely attenuated by pretreatment with dimethylthiourea (DMTU, a h ydroxyl radical scavenger), indomethacin (Indo, a cyclo-oxygenase inhi bitor), or both DMTU and Indo (DMTU + Indo). Conversely, the peak resp onses of RARs were not significantly affected by pretreatment with iso prenaline (a bronchodilator) or vehicle for these chemicals. Additiona lly, pretreatment with DMTU, Indo, or DMTU + Indo did not significantl y alter the RAR sensitivity to mechanical stimulation (constant-pressu re lung inflation; 20 cmH(2)O). 4. Of the nine RARs tested, six were s timulated by histamine and their sensitivity to this chemical irritant was not altered by pretreatment with DMTU + Indo. 5. The results sugg est that both the particulates and gas phases are responsible for, and both the hydroxyl radical and cyclo-oxygenase products are involved i n, the stimulation of RARs by wood smoke. Furthermore, changes in lung mechanics following smoke delivery are not the cause of this afferent stimulation.