An Experimental Study on Epithelial Proliferation Related to Localized Fibrosis in the Lung

Abstract

This experiment was intended to evaluate the relationship between pre-existing localized fibrosis and epithelial hyperplasia of the lung.
Male rats (S.D. strain) received an intravenous injection of tetrachlorodifluoroethane. This resulted in localized fibrosis in the lung. Three months after the injection these animals were given intratracheal injections of 3 mg. of benzo (a) pyrene or ³Hbenzo (a) pyrene once a week, for a total of 15 times.
The lungs of these animals were examined histopathologically, autoradiographically, and electron microscopically.
Proliferation of cuboid epithelial cells was found around the fibrotic lesions of the lung. Proliferated epithelial cells were identical with nonciliated bronchiolar epithelium (Clara cell) or occasionally Type II alveolar cells electron microscopically.
³H-benzo (a) pyrene deposited in the localized fibrotic lesion 17 months after completion of the 15 weekly injections of ³H-benzo (a) pyrene, though deposition of ³Hbenzo (a) pyrene was found diffusely in the lung 2 days after the administration of ³Hbenzo (a) pyrene.
These findings indicate that clearance ability is reduced in the localized fibrotic lesions in the lung. We consider that localized pulmonary fibrosis is a contributing factor in epithelial hyperplasia of the lung.