Alterations in the cellular population of the alveolar wall in an animal model of fibrosis. A morphometric study.

A reproducible animal model of interstitial pulmonary fibrosis is generated in rodents by intratracheal in jection of the antineoplastic drug, b leomycin sulfate. Pulmonary lesions resemble closely those observed in human patients with fibrosis. Fibrot ic lesions are most pronounced 3 4 weeks after the drug's instil lation. 1 Histologically, increased interstitial connect ive tissue and hypercellularity are observed. ' B iochemical assays reveal increased lung collagen and elast in, 2 and physiologic measurements show reduced compliance and decreased lung volumes, as those observed in humans with the d i s e a s e . 3 4 Apparent increases in nonmuscle contracti le cells in interstitial regions of humans with fibrosis5 and in rats with fibrosis induced by intratracheal injection o f b leomyc in 6 have b e e n reported. T h e s e observations correlate well with increased contracti le capability of parenchymal strips of lung isolated from fibrotic humans (biopsy and surgical t issue) ' and bleomycintreated rats 6 and increased content of nonmuscle contracti le proteins in bleomycin rat lung t i s sue . 8 This study used ultrastructural stereologic methods to examine quantitative alterations in nonmuscle contracti le interstitial cells (CIC) in lungs of rats 4 weeks after instillation of bleomycin.