To obtain an experimental model of idiopathic pulmonary fibrosis and its early changes (fibrosing alveolitis), lung injuries were produced in rats with repeated injections of paraquat. Most of the animals died in a few days after single intraperitoneal injection of a moderate amount (more than 20mg per kg of body weight) of paraquat. Pathologic findings in the lungs were hemorrhagic pulmonary edema. However, with reduced amounts of paraquat (5 or 10mg per kg) most of the animals survived. In some of the animals with repeated injections of paraquat, moderate interstitial pneumonia developed. In addition, repeated injections (twelve times, every ten days) produced typical interstitial pneumonia in 30.7 or 36 percent of the animals with intraperitoneal or subcutaneous injections of 10mg per kg, respectively.
These results reveal that paraquat-induced lung injury is an effective method to produce chronic interstitial pneumonia in rats. In the pathogenesis, repeated alveolar cell damage with interstitial edema of the alveoli was discussed as an important factor.