LONG-TERM CIGARETTE-SMOKE EXPOSURE DOES NOT INCREASE AIRWAY RESPONSIVENESS IN RATS

To ascertain whether chronic cigarette smoke exposure induces increase d airway responsiveness, we performed methacholine response tests in S prague-Dawley rats by calculating pulmonary resistance after nebulizat ion of-saline followed by an increasing concentration of methacholine. We also calculated the concentration of methacholine which doubled th e baseline resistance (R200). Tests were performed at baseline and aft er 2, 4, 8, and 12 months of exposure to the smoke of seven cigarettes per day, 5 days each week; control animals were exposed to room air. At the completion of the study, there were 13 rats in the smoke-expose d group and 7 rats remaining in the control group. Airway morphology w as assessed using a point counting technique. We found that (1) chroni c exposure to cigarette smoke did not alter either the baseline resist ance or the R200; (2) the saline baseline resistance decreased over ti me in the control animals; and (3) at the 12-month time point, smokers with increased baseline airway resistance had greater amounts of airw ay smooth muscle compared with the smoke-exposed animals without incre ased resistance. We conclude that in this animal model, long term expo sure to cigarette smoke did not alter the response to methacholine but did increase airway smooth muscle and baseline resistance in some but not all animals.