Injury to type-2 pneumocytes in rats exposed to cigarette smoke

Ultrastructural and biochemical assessment has been made of injury to the lower respiratory tract following inhalation exposure of rats to cigarette smoke. Rats were held in a smoke chamber for up to 100 min/day for periods of at least 15 days and, in some cases, of 45 days. Incorporation of radioactive precursors into DNA and RNA isolated from whole lung was not significantly affected by this treatment. However, determination of surfactant recovered by endobronchial lavage revealed a progressive reduction during the first 15 days of exposure followed by a reduced but stabilized recovery up to 45 days. Depression of surfactant yield invariably followed cigarette smoke exposure but a simple dose-response relationship was not observed. These findings could be related to progressive injury to Type 2 pneumocytes as determined by electron microscopy. Examination of lung tissue at weekly intervals during continuous smoke exposure for up to 20 days revealed no consistent ultrastructural alteration. Exposure to cigarette smoke for 25 days produced distortion of the pulmonary parenchyma, with seemingly excessive numbers of lamellar bodies in hypertrophied Type-2 pneumocytes, associated with areas of alveolar collapse. These enlarged cells became embedded in the distorted interstitium after 40-days' treatment, and by 50 days a significant number of Type-2 cells showed loss of lamellar bodies and elongation of cytoplasm. The Type-1 pneumocytes appeared normal throughout the period of exposure.