study of the sequence of changes in the lungs of rats chronically exposed to silica dust

ABSTRACT

Histopathological and enzyme histochemical changes were studied in lungs of rats chronically exposed to silica-bearing dust. The early histopathological changes were in the form of an inflammatory reaction consisting of polymorphonuclear neutrophils, macrophages and lymphocytes, while after prolonged exposure, lymphocytes and plasma cells predominated and the alveolar walls were thickened and showed increased deposition of recticulin and collagen fibres. These changes were accompanied by alteration in the activities of the phosphatase, non-specific esterase, succinic dehydrogenase and cytochrome oxidase enzymes in the alveolar and bronchilar epithelium and in the macrophages. The presented findings might lead to the suggestion that, following inahalation of silica-bearing dust, an inflammatory reaction develops in the lungs of the exposed animals. The stimulated macrophages release hydrolytic enzymes which produce destruction of lung parenchyma, hence antigenic material is released by the destroyed lung tissue evoking an immunological inflammatory reaction and thus augmenting the process of tissue destruction which precedes fibrogenesis