Objective    To investigate the roles of activin A (ACT-A) and follistatin (FS) in renal interstitial fibrosis.     Methods    Renal interstitial fibroblasts were isolated from SD rat kidney and primarily cultured. The cells were divided into A group

F group and A+F group

and then each group was further divided into 5 subgroups according to their culture media being added with ACT-A (0

0.3

3

30

or 100 ng/ml)

FS (0

0.3

3

30

or 100 ng/ml)

and ACT-A (30 ng/ml) plus FS (0

0.3

3

30

or 100 ng/ml) respectively. Levels of type Ⅳ collagen (Ⅳ-C) and hydroxyproline (HYP) in the supernatants of cultured fibroblasts were measured by ELISA assay.     Results    Concentrations of Ⅳ-C and HYP in cultured rat renal interstitial fibroblasts were in a dose-dependent manner with ACT-A treatment. FS had no effect on these concentrations

but it inhibited the effects of ACT-A on Ⅳ-C and HYP in the supernatants of cultured fibroblasts in a dose-dependent manner.     Conclusion    ACT-A might be involved in occurrence and development of renal fibrosis by affecting renal interstitial fibroblasts. Exogenous FS could suppress the effects of ACT-A on the cultured renal fibroblasts.