BACKGROUND:The pathogenesis of hepatic ifbrosis and cirrhosis is still not fully understood. The extracellular signal-regulated kinase (ERK) pathway is involved in the regulation of cell proliferation and differentiation. The aim of this study was to investigate the effects of PD98059, a speciifc inhibitor of ERK, on the cell cycle, cell proliferation, secretion of typeⅠcollagen and expression of cyclin D1 mRNA, CDK4 mRNA and transforming growth factor-β1 (TGF-β1) mRNA in rat hepatic stellate cells (HSCs) stimulated by acetaldehyde. METHODS:Rat HSCs stimulated by acetaldehyde were incubated with PD98059 at different concentrations. The cell cycle was analysed by lfow cytometry. Cell proliferation was assessed by the methyl thiazolyl tetrazolium colorimetric assay. The mRNA expression of cyclin D1, CDK4 and TGF-β1 was examined using the reverse transcriptase-polymerase chain reaction. Type Ⅰcollagen in the culture medium was detected by enzyme-linked immunosorbent assay. RESULTS: 20, 50 and 100 μmol/L PD98059 signiifcantly inhibited the proliferation and provoked a G0/G1-phase arrest of acetaldehyde-induced HSCs in a dose-dependent manner. The secretion of typeⅠ?collagen and the expression of cyclin D1, CDK4 and TGF-β1 mRNA in acetaldehyde-induced HSCs were markedly inhibited by 50 and 100μmol/L PD98059, respectively. CONCLUSIONS:The ERK pathway regulates the cell proliferation, secretion of type Ⅰ collagen and the expression of TGF-β1 mRNA in rat HSCs stimulated by acetaldehyde, which is likely related to its regulative effect on the cell cycle.