EFFECTS OF SIDESTREAM SMOKE EXPOSURE AND AGE ON PULMONARY-FUNCTION AND AIRWAY REACTIVITY IN DEVELOPING RATS

Children exposed to environmental tobacco smoke (ETS) in their homes have increased cough, respiratory illness, airway obstruction, and hyperreactivity. Since an animal model is needed to understand the mechanism by which this occurs, our study was designed to determine if immature rats develop airway obstruction and increased airway reactivity when exposed to sidestream smoke (SSS, respirable suspended particulate concentration 1.00 +/- 0.03 mg/m3, CO concentration 6.48 +/- 0.29 ppm). In the first of 3 studies, rats were exposed to filtered air (FA) or SSS for 6 hr/day, 5 days/week from day 2 to week 8 or week 15 of life (n = 6-8 in each group). SSS exposure did not change lung resistance (R(L)), dynamic lung compliance (C(Ldyn)), lung weight/body weight ratio (LW/BW), pulmonary artery pressure (P(PA)), body weight, or airway reactivity to methacholine (all P > 0.2, 2-way ANOVA). Regardless of exposure, lungs from younger rats were relatively heavier and more reactive to methacholine than lungs from older rats (P < 0.05, 2-way ANOVA). In the second study, 15-week-old rats were exposed to FA or SSS for 3 hr or for 4 days (6 hr/day, n = 6 in each group). SSS exposure again had no effect on C(Ldyn), R(L), LW/BW, P(PA), or airway reactivity to methacholine (all P > 0.2, ANOVA). In the third study, rats were exposed to FA or SSS from day 2 to week 11 of life (n = 7 in each group). SSS exposure reduced airway (P = 0.004) but not pulmonary artery (P = 0.63) reactivity to serotonin. We conclude that (1) SSS exposure to the immature rats did not mimic the effects of ETS seen in children, (2) younger rats had greater muscarinic airway reactivity than older rats, and (3) serotonin may play a role in ETS-induced lung problems. (C) 1993 Wiley-Liss, Inc.