Idiopathic pulmonary fibrosis(IPF) is a devastating illness for which there is little effective treatment. The key cytokines currently implicated in the fibrotic process are the transforming growth factor-β₁(TGF-β₁), tumor necrosis factor-α(TNF-α), endothelin-1(ET-1) and interferon-γ(IFN-γ). The rat model for paraquat-induced pulmonary fibrosis was chosen to investigate the role of ET-1 in this disease. Both ET-1 and TGF-β₁ expression in lung lesions were examined using immunohistochemical staining. After Bosentan® administration, an orally active ET-1A and ET-1B receptor antagonist, the degree of pulmonary fibrosis and ET-1 and TGF-β₁ expression were analyzed.

Sprague-Dawley rats were divided into three groups, the control group, the fibrosis group, and the fibrosis-Bosentan®-treated group. The animals were sacrificed periodically at 1, 3, 5, 7, 10, 14 days after administering saline or paraquat. The effects between groups were compared with the results of light microscopy and immunohistochemical staining for ET-1 and TGF-β₁. The degree of fibrosis was evaluated by H&E and Masson's trichrome staining, which were graded by a computerized image analyzer. The degree of immunohistochemical staining was categorized by a semi-quantitative analysis method.

The lung collagen content had increased in the paraquat instillated animals by day 3, and continued to increase up to day 14. A daily treatment by gavage with Bosentan®(100mg/kg) did not prevent the increase in collagen deposition on the lung that was induced by paraquat instillation. There were increased imunohistochemical stains of ET-1 on the exudate, macrophages, vascular endothelial cells and pneumocytes in the paraquat instillated group. Furthermore, TGF-β₁ expression was higher on the exudate, macrophages, some infalmmatory cells, pneumocytes(type I, and II), vascular endothelium and the respiratory epithelial cells around the fibrotic area. After Bosentan treatment, there were no definite changes in ET-1 and TGF-β₁ expression.

Fibrosis of the Paraquat instillated group was more advanced when compared with the control group. In addition, there was increased ET-1 and TGF-β₁ expression around the fibrotic area. ET-1 is associated with lung fibrosis but there was little effect of the ET-1 receptor blocker(Bosentan®) on antifibrosis.