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Comparison has been made of injury to the rat pulmonary alveolar parenchyma evoked by intravenous injection of N-nitrosomethylurethane, intratracheal instillation of 3-methylcholanthrene or repeated inhalation for up to 15 days of carbon tetrachloride, trichloroethylene or gasoline vapour. Biochemical analyses, including assessment of rates of RNA and DNA synthesis and secretion of pulmonary surfactant, were correlated with morphological changes determined by electron microscopy. Single doses of N-nitrosomethylurethane or 3-methylcholanthrene inhibited incorporation of [14C] orotate into lung RNA 1--3 days after treatment. Daily exposure for 30 min to carbon tetrachloride or trichloroethylene vapour caused less marked reduction in orotate incorporation. Ultrastructural examination revealed that 3-methylcholanthrene toxicity was characterised by cytoplasmic change including disruption of surfactant lamellaie of Type 2 pneumocytes and variable degenerative changes Type 1 pneumocytes. Eight to ten days after treatment, the morphological evidence of hypertrophy/hyperplasia and transformation of Type 2 pneumocytes correlated well with biochemical evidence of stimulated incorporation of [3H]thymidine. Inhalation of carbon tetrachloride or trichloroethylene vapour produced milder responses including occasional degenerative changes in Type 1 pneumocytes, reduced numbers of surfactant lamellae in Type 2 pneumocytes and no change in [3H]thymidine incorporation. In contrast to the gradation of injury produced by the various chemicals, all procedures caused a marked and reproducible reduction in secretion of pulmonary surfactant as determined by endobronchial lavage. Following solvent inhalation, reduced recovery of surfactant was detected within 5 days of repeated exposure and thereafter no further change in this depressed level resulted from continued exposure for a further 10 days. The data are discussed in terms of a generalised pattern of response by pulmonary alveolar tissue to chemical injury and the apparent sensitivity of surfactant secretion as an indicator of damage to the lung.

Repeated exposure of rats to trichloroethylene, carbon tetrachloride, gasoline vapour or to cigarette smoke is followed by significant reduction in the recovery of pulmonary surfactant, inhibition being evident as early as 5 days after commencement of treatment. The degree of reduction in surfactant recovery was dose-dependent and the kinetics of this reaction indicated the relative toxicities of the treatments. The results are discussed with reference to the use of surfactant recovery as an indicator of non-specific injury to respiratory tissue.

Cell lines which exhibit epithelial morphology with surface microvilli and inclusion bodies characteristic of type 2 pneumocytes have been derived from normal adult mouse lung by a simple procedure involving enzymatic dispersal and mechanical elimination of other cell types. One of these cell lines designated NAL 1A, examined in detail, shows features consistent with its being related to type 2 pneumocytes of mouse lung. These features include desmosomes, dense lamellar bodies as well as phospholipid profiles related to immature surface active material, the inhibition of cell growth rate by dexamethasone, and the close similarity of the cytoskeletal protein patterns of this cell line to those of a metastatic type 2 pneumocyte-related cell line of mouse lung. The cell line from normal lung demonstrated near diploid chromosome number at low passage number with some evidence of karyotype instability at high passage number.

Inhalation of air contaminated with petrol vapour has been shown to produce reduced surfactant levels in the lungs of rats. Pulmonary surfactant was obtained by endobronchial lavage followed by salt extraction and freeze drying to obtain the dry, hydrophobic product. During 45 days of continuous exposure, the lowest yield of surfactant was obtained after 15 days of treatment. During the following 30 days of treatment, the surfactant yield reached a relatively constant level, approximately half the mean value for control animals. Chromatographic analysis indicated no qualitative alteration in the phospholipid components of surfactant with increasing times of exposure to the irritant. It has been possible to correlate biochemical evidence of toxic lung injury with signs of cellular damage obtained from ultrastructural studies.

Epithelial cell strains, designated NAL, have been established from normal lungs of adult female Balb/c mice. The ultrastructural characteristics, effect of dexamethasone on cellular morphology and proliferation rate, and the cytoskeletal protein pattern of NAL suggests that these cell strains may be related to a urethane-induced mouse lung adenoma cell strain NUL and to a metastasizing mouse lung tumour cell line CMT. NAL exhibited no anchorage-independent growth under normal conditions, however extensive passaging in the presence of 5 X 10(-6)M dexamethasone resulted in a colony forming efficiency in soft agar of 8.4% at passage number 30.

Rats exposed to an atmosphere contaminated with petrol vapour at a concentration of 100 parts per million for up to 12 weeks exhibit a high incidence of electron microscopic changes in the lung parenchyma characterized by interstitial fibrosis with associated alveolar collapse. Initial changes appearing after 6 weeks include degeneration of endothelium and interstitial fibroblasts followed by hypertrophy of Type 2 pneumocytes. Subsequent degeneration of surfactant organelles of the hypertrophied Type 2 pneumocytes correlates with the appearance of focal alveolar collapse and associated interstitial fibrosis. Because of the rapidity with which lesions are induced in the rat lung, this experimental technique provides an economical and reproducible model for an integrated study of the sequential morphological and biochemical events preceding pulmonary fibrosis which might well lead to a better understanding of the enigmatic human syndrome of fibrosing alveolitis.