To clarify the mechanism underlying the preventive effect of
baicalin (Bai) on
fibrosis in lung, we investigated the influence of Bai on the up-regulation of
connective tissue growth factor (CTGF) in fibrotic lungs. Male Sprague-Dawley (SD) rats were divided into four groups randomly:
normal saline (NS)+NS group (a single intratracheal instillation of NS plus i.p. injection of NS), NS+Bai group (intratracheal instillation of NS plus i.p. injection of Bai),
bleomycin (BLM)+NS group (intratracheal instillation of BLM plus i.p. injection of NS) and BLM+Bai group (intratracheal instillation of BLM plus i.p. injection of Bai). All the i.p.
injections were performed once daily. On day 28 after intratracheal instillation of BLM or NS, the rats were sacrificed for lung tissue sampling. As the index of the severity of
pulmonary fibrosis, the content of
hydroxyproline in lungs was analyzed by
chloramine T method. The expression levels of CTGF
mRNA and
protein in the lungs were detected by RT-PCR and immunohistochemistry, respectively. The results showed that, compared to the rats in NS+NS group, the rats in BLM+NS group showed increased
hydroxyproline content and higher levels of CTGF
mRNA and
protein expressions (P<0.01), suggesting that BLM had induced
fibrosis in lung and up-regulated CTGF expression in the fibrotic lungs. Administration of different dosages of Bai (6, 12.5 and 50 mg/kg per d, for 28 days) into the BLM-treated rats reduced the increased content of
hydroxyproline, and ameliorated the up-regulation of CTGF
mRNA and
protein levels, respectively. These results suggest that Bai could prevent the up-regulation of CTGF expression in fibrotic lungs of rats receiving BLM instillation, which might be one of the mechanisms underlying the preventive effect of Bai on
pulmonary fibrosis.