AIM: To investigate the effect of various concentrations of tetrandrine on activation of quiescent rat hepatic stellate cells (HSCs) and transforming growth factor-β(TGF-β) signaling in vitro. METHODS: HSCs were isolated from rats by in situ perfusion of liver and 18% Nycodenz gradient centrifugation, and primarily cultured on uncoated plastic plates for 24 h with DMEM containing 20% fetal bovine serum (FBS/ DMEM) before the culture medium was substituted with 2% FBS/DMEM for another 24 h. Then, the HSCs were cultured in 2% FBS/DMEM with tetrandrine (0.25, 0.5, 1, 2 mg/L, respectively). Cell morphological features were observed under an inverted microscope, smooth muscle-α-actin (α-SMA) was detected by immunocytochemistry and image analysis system, laminin (LN) and type Ⅲ procollagen (PCⅢ) in supernatants were determined by radioimmunoassay. TGF-β1 mRNA, Smad 7 mRNA and Smad 7 protein were analyzed with RT-PCR and Western blotting, respectively. RESULTS: Tetrandrine at the concentrations of 0.25-2 mg/L prevented morphological transformation of HSC from the quiescent state to the activated one, while α-SMA, LN and PCⅢ expressions were inhibited. As estimated by gray values, the expression of α-SMA in tetrandrine groups (0.25, 0.5, 1, 2 mg/L) was reduced from 21.3% to 42.2% (control: 0.67, tetrandrine groups: 0.82, 0.85, 0.96, or 0.96, respectively, which were statistically different from the control, P<0.01), and the difference was more significant in tetrandrine at 1 and 2 mg/L. The content of LN in supernatants was significantly decreased in tetrandrine groups to 58.5%, 69.1%, 65.8% or 60.0% that of the control respectively, and that of PCⅢ to 84.6%, 81.5%, 75.7% or 80.7% respectively (P<0.05 vs control), with no significant difference among tetrandrine groups. RT-PCR showed that TGF-β1 mRNA expression was reduced by tetrandrine treatments from 56.56% to 87.90% in comparison with the control, while Smad 7 mRNA was increased 1.4-4.8 times. The TGF-β1 mRNA and Smad 7 mRNA expression was in a significant negative correlation (r= -0.755, P<0.01), and both were significantly correlated with α-SMA protein expression (r= -0.938, P<0.01; r = 0.938,P<0.01, respectively). The up-regulation of Smad 7 protein by tetrandrine (1 mg/L) was confirmed by Western blotting as well. CONCLUSION: Tetrandrine has a direct inhibiting effect on the activation of rat HSCs in culture. It up-regulates the expression of Smad 7 which in turn blocks TGF-β1 expression and signaling. AIM: To investigate the effect of various concentrations of tetrandrine on activation of quiescent rat hepatic stellate cells (HSCs) and transforming growth factor-β (TGF-β) signaling in vitro. Methods: HSCs were isolated from rats by in situ perfusion of liver and 18% Nycodenz gradient centrifugation, and was cultured on uncoated plastic plates for 24 h with DMEM containing 20% ​​fetal bovine serum (FBS / DMEM) before the culture medium was substituted with 2% FBS / DMEM for another 24 h. HSCs were cultured in 2% FBS / DMEM with tetrandrine (0.25, 0.5, 1, 2 mg / L, respectively). Cell morphological features were observed under an inverted microscope, smooth muscle-α-actin Immunocytochemistry and image analysis system, laminin (LN) and type Ⅲ procollagen (PCⅢ) in supernatants were determined by radioimmunoassay. TGF-β1 mRNA, Smad 7 mRNA and Smad 7 protein were analyzed with RT-PCR and Western blotting respectively. Tetrandrine at the con As estimated by gray values, the expression of α-SMA in tetrandrine groups ( 0.25, 0.5, 1, 2 mg / L) was reduced from 21.3% to 42.2% (control: 0.67, tetrandrine groups: 0.82, 0.85, 0.96, or 0.96, respectively, which were statistically different from the control, P <0.01) , and the difference was more significant in tetrandrine at 1 and 2 mg / L. The content of LN in supernatants was significantly less in tetrandrine groups to 58.5%, 69.1%, 65.8% or 60.0% that of the control respectively, and that of RT-PCR showed that TGF-β1 mRNA expression was reduced by tetrandrine treatments from 56.56% to 87.90 (P <0.05 vs. control), PCⅢ to 84.6%, 81.5%, 75.7% or 80.7% respectively % in comparison with the control, while Smad 7 mRNA was increased 1.4-4.8 times. The TGF-β 1 mRNA and Smad 7The mRNA expression was in a significant negative correlation (r = -0.755, P <0.01), and both were significantly correlated with α-SMA protein expression (r = -0.938, The up-regulation of Smad 7 protein by tetrandrine (1 mg / L) was confirmed by Western blotting as well. Tetrandrine has a direct inhibiting effect on the activation of rat HSCs in culture. It up-regulates the expression of Smad 7 which in turn blocks TGF-β1 expression and signaling.