Objective To investigate the optimal dosage of pirfenidone for the treatment of pulmonary fibrosis induced by bleomycin in Wistar rats

and the alteration of expressions of transforming growth factor beta-1 （TGF-β

1）

tissue inhibitor of metalloproteinase-1 （TIMP-1）

and matrix metalloproteinase-13 （MMP-13） in lung tissue. Methods Male Wistar rats were endotracheally instilled with bleomycin or normal saline. Pirfenidone （25-[KG*8]800 mg·kg -1·d -1）

dexamethasone （3 mg/kg）

or 1% carboxymethylcellulose sodium were given daily by feed 2 days before instillation of bleomycin. Groups T7 and T14 were fed pirfenidone 50 mg·kg -1·d -1 at 7 days or 14 days after bleomycin instillation. Lungs were harvested at 28 days after bleomycin instillation. Patholological changes in lung tissues were evaluated with HE staining. Lung collagen was stained by sirius red and measured by content of hydroxyproline. Expression of proteins of TGF-β

1

TIMP-1

and MMP-13 were detected by Western blotting. Results At doses of 25

50

and 100 mg·kg -1·d -1

pirfenidone had significant anti-fibrotic effects for bleomycin-induced rat pulmonary fibrosis

and these effects were most significantly attenuated at the dosage of 50 mg·kg -1·d -1 （HE: P

<

0.01

P

<

0.01

and P=0.064; sirius red: P

<

0.05

P

<

0.01

and P

<

0.05; hydroxyproline: P=0.595

P

<

0.01

and P=0.976）. Pirfenidone at a dosage of[KG*3]50 mg·kg -1·d -1 inhibited protein expression of TGF-β

1 and TIMP-1 in lung tissue in the early phase （0.79 and 0.75 times of control group）

but had no effect on expression of MMP-13. Conclusion Low dose pirfenidone

especially at dosage of 50 mg·kg -1·d -1

has significant anti-fibrotic effects on bleomycin-induced rat pulmonary fibrosis. Pirfenidone partially inhibits the enhancement of the expression of TGF-β

1 and TIMP-1 in lung tissue.