Background Environmental problems are increased dramatically in modern society. For example, dust, residual pesticides, and allergens can cause pulmonary fibrosis. At present, there are no effective methods and drugs to alleviate the progression of pulmonary fibrosis. Traditional Chinese medicine has received increasing attention for its potential therapeutic effect on the disease.

Objective This experiment tests the therapeutic effect of Brassica rapa L. extract on pulmonary fibrosis induced by bleomycin, and explores relevant mechanism.

Methods Fifty SD rats were randomly divided into a control group, a model group, a dexamethasone group (1 mg·kg^-1, intraperitoneal injection), and two Brassica rapa L. groups (25 and 50 g·kg^-1, intragastrical administration). Except the control group, the other groups of rats were transtracheally injected with bleomycin (5 mg·kg^-1) to establish a pulmonary fibrosis model. After 7 d, intraperitoneal injection of dexamethasone and intragastric administration of Brassica rapa L. extract lasted for 21 d. Body weight changes were observed. Rat lung forced vital capacity (FVC), forced expiratory volume in one second (FEV1), and peak expiratory flow (PEF) were measured with a rat pulmonary function meter. Lung coefficient was calculated. Histomorphological changes of lung were evaluated after HE staining. The expressions of collagenⅠand collagen Ⅲ in lung tissues were detected after immunohistochemical staining. The contents of collagenⅠ, collagen Ⅲ, and inflammatory factorstumor necrosis factor-α (TNF-α) and interleukin 6 (IL-6) in lung tissues were detected by enzymelinked immunosorbent assay.

Results Compared with the model group, on day 28, the body weight of rats in the 50 g·kg^-1 Brassica rapa L. group was increased significantly(262.7±30.2) g vs (235.4±38.9) g, P < 0.05; the FVC, FEV1, and PEF of rats in the 25 and 50 g·kg^-1 Brassica rapa L. groups were increased(6.15±0.28), (6.81±0.36) mL vs (4.85±0.25) mL; (7.22±0.31), (7.86±0.28) mL vs (5.92±0.23) mL; (30.61±8.88), (32.14±6.27) mL vs (24.65±6.12) mL, P < 0.05, accompanied with decreased lung coefficient(0.58±0.09)%, (0.53±0.10)% vs (0.73±0.14)%, P < 0.05), reduced inflammatory cell infiltration in lung tissues, less rupture of alveolar wall and fusion of alveolar cavity, and alleviated pulmonary fibrosis; the expression levels of collagen Ⅰ and collagen Ⅲ in lung tissues of rats in the 50 g·kg^-1 Brassica rapa L. group were decreased(2.15±0.56) mg·L^-1 vs (2.82±0.55) mg·L^-1, (2.35±0.58) mg·L^-1 vs (3.02±0.59) mg·L^-1, P < 0.05; the expression levels of inflammatory factors TNF-α and IL-6 in lung tissues of rats in the 25 and 50 g·kg^-1 Brassica rapa L. groups were decreased(397.59±73.73), (363.65±66.06) ng·L^-1 vs (554.59±115.81) ng·L^-1; (194.71±37.74), (166.20±28.33)ng·L^-1 vs (253.39±72.14) ng·L^-1, P < 0.05.

Conclusion Brassica rapa L. may alleviate the pathological process of pulmonary fibrosis caused by bleomycin in rats via inhibiting the fibrosis caused by collagenⅠ, collagen Ⅲ, and the inflammatory factors TNF-α and IL-6.