Abstract: Objective To study the pathology and possible mechanism of pulmonary fibrosis in rats induced by experimental hydrochloric acid (HCl) inhalation and compared with traditional bleomycin-induced fibrosis. Method One-hundred and twenty male SD rats were randomly divided into nomal control, bleomycin，high，middle and low-dose HC1 group.The bleomycin group was intratracheally injected bleomycin, the HC1 groups were intratracheally injected HC1 once per week, and the control group was given saline in the same way.Six rats of each group were randomly sacrificed on day 7，14，28 and 42 respectively. The histological changes of the lung tissue were evaluated by HE and Masson's trichrome staining. The mRNA expression of transforming growth factor-β＜sub＞1＜/sub＞(TGF-β＜sub＞1＜/sub＞) were assayed by RT-PCR. The CTGF expression were analyzed by immunohistochemistry. Results Hydrochloride groups has significantly higher alveolitis levels (P＜0.01) and can reach or exceed the level of bleomycin group after 28d. Fibrosis in hydrochloric acid groups were increased gradually over time，but not consistently exceeded bleomycin group (P＞0.05). Similar results appear in the TGF-β₁ mRNA and CTGFexpression in immunohistochemical identification. Conclusion The results revealed the relationship between the gastroesophageal reflux disease (GERD) and idiopathic pulmonary fibrosis (IPF).

Key words: Pulmonary fibrosis, GERD, Hydrochloric acid, Bleomycin