Paraquat-induced pulmonary fibrosis starts at an early stage of inflammation in rats

Aim: To investigate the starting point of paraquat-induced pulmonary fibrosis in rats. Materials & methods: A total of 96 healthy Sprague Dawley rats were randomly divided into eight groups (n = 12 in each group) including a control and paraquat-poisoning group. Control rats received treatment with saline. Samples were collected at 2, 6, 12, 24, 48, 72 and 120 h after paraquat administered by lavage. All lung tissues were stained with hematoxylin eosin and Masson's trichrome. Collagen III expressed in bronchoalveolar lavage fluid was detected by ELISA. The a-smooth muscle actin in lung tissue was detected by western blotting. Results: A rat model of paraquat poisoning was established. Histological examination results indicated that lung fibrosis started in rats 2 h after paraquat poisoning. Compared with the control group, the collagen III protein in bronchoalveolar lavage fluid was significantly upregulated in the 2-h group (alpha = 0.05) and the same level was maintained in the other poisoning groups. The expression of a-smooth muscle actin in the lung tissue was significantly increased in the 12-h group (alpha = 0.05) and remained at the same level after 12 h. Conclusion: The paraquat-induced pulmonary fibrosis in rats began at an early stage of inflammation. The therapy of antifibrosis should be applied at an early time of paraquat poisoning.