INHIBITORY EFFECT OF INHALED WOOD SMOKE ON THE DISCHARGE OF PULMONARYSTRETCH RECEPTORS IN RATS

We investigated the inhibition of slowly adapting pulmonary stretch re ceptors (PSRs) by inhaled wood smoke. Impulses were recorded from PSRs in 68 anesthetized, open-chest, and artificially ventilated rats. Eig hty-one of one hundred five PSRs were inhibited within one or two brea ths when 6 ml of wood smoke were delivered into the lungs. As a group (n = 105), PSR activity significantly decreased from a baseline of 19. 0 +/- 1.3 (SE) to a lowest level of 12.9 +/- 1.2 impulses/breath at th e fourth or fifth breath after smoke delivery. This afferent inhibitio n usually persisted for 5-18 breaths. In contrast, smoke delivery did not affect transpulmonary pressure. Delivery of gas-phase smoke or a h ypercapnic gas mixture containing CO2 at a concentration (15%) matchin g that in the smoke produced a nearly identical inhibition in the same PSRs (n = 10). This afferent inhibition was largely prevented by pret reatment with acetazolamide (an inhibitor of carbonic anhydrase; n = 1 0) but was not affected by pretreatment with the vehicle for acetazola mide (n = 8) or isoproterenol(a bronchodilator; n = 10). These results suggest that 1) an increase in H+ concentration resulting from hydrat ion of CO2 in the smoke may be responsible for the inhibitory effect o f wood smoke on the discharge of PSRs and 2) changes in lung mechanics are not the cause of this afferent inhibition.