[Scanning electron microscopic study of rat lungs in experimental chronic paraquat poisoning]

It is well known that Paraquat (1,1'-dimethyl-4,4'-bipyridylium dichloride), used widely as a herbicide, causes a primary toxic effect in the lungs of humans and laboratory animals. This paper describes the pulmonary changes of chronic paraquat poisoning in rats, comparing scanning electron microscopic findings. Twenty-four rats were given repeated injections of 10/kg body weight paraquat intraperitoneally for 6 consecutive months, and six control rats were given 0.9% NaCl solution. The animals exposed to paraquat showed thickening of alveolar septum, inflammatory cell infiltration, interstitial fibrosis, and marked proliferation of alveolar macrophages. Among them four rats (21%) showed the typical findings of diffuse pulmonary fibrosis. Lesions were more severe at the subpleural region of the lung. The desquamation of alveolar epithelial cells and subsequent exposure of the basement membranes were observed in places. Although alveolar epithelial cells both in the type I and the type II were prolific, the type II cells showed partial loss of microvilli and projections. These findings may indicate the lowering of the type II cell function and subsequent decrease of surfactant excretion which causes respiratory insufficiency. Furthermore, alveolar macrophages showed a tendency to increase in number with progressive development of fibrosis. This tendency may support the hypothesis by Schoenberger et al., in which alveolar macrophages release both fibronectin and a growth factor for fibroblast after paraquat exposure.