Sidestream Smoke Effects on Lung Morphology and C-Fibers in Young Guinea Pigs

Children raised in homes with smokers have more frequent respiratory symptoms, decreased lung function, and increased airway reactivity. This study was designed to evaluate whether chronic exposure of developing guinea pigs to sidestream smoke (SS) would impair lung function and morphology and/or change the activity of a pulmonary defense mechanism, the local bronchopulmonary C-fiber system. Duncan-Hartley guinea pigs (n = 29) were exposed to filtered air (FA) or to SS for 6 h/day, 5 days/week from 8 to about 43 days of life. Their lungs were then studied in an isolated buffer perfused system where increasing doses of capsaicin (a C-fiber stimulant) or substance P (SP, a C-fiber neurotransmitter) were injected into the pulmonary artery. SS exposure significantly increased baseline dynamic compliance (C_dyn) by 17% but did not change baseline pulmonary resistance (R_L). SS exposure reduced the capsaicin-induced change in R_L and C_dyn but did not change lung responsiveness to SP. SS exposure did not change fixed lung volume, surface area, mean linear intercept length, or elastin deposition. We conclude that SS exposure to developing guinea pigs (1) increased lung compliance without affecting alveolar size or elastin deposition and (2) decreased the airway reactivity of the C-fiber system without changing reactivity to one of its neurotransmitters, SP. If humans are similarly affected, children raised in the homes of smokers may have a diminished pulmonary defense mechanism.