Aim:To investigate the effects of onychin on the proliferation of cultured ratartery vascular smooth muscle cells(VSMCs)in the presence of 10% new-borncalf serum(NCS).Methods:Rat VSMCs were incubated with onychin 1-50μmol/L or genistein 10μmol/L in the presence of 10% NCS for 24 h.The prolif-eration of VSMCs was measured by cell counting and MTS/PMS colorimetricassays.Cell cycle progression was evaluated by flow cytometry.Retinoblastoma(Rb)phosphorylation,and expression of cyclin D_1 and cyclin E were measured byWestern blot assays.The tyrosine phosphorylation of ERK1/2 was examined byimmunoprecipitation techniques using anti-phospho-tyrosine antibodies.Results:The proliferation of VSMCs was accelerated significantly in the presence of 10%NCS.Onychin reduced the metabolic rate of MTS and the cell number of VSMCsin the presence of 10% NCS in a dose-dependent manner.Flow cytometry analy-sis revealed that the G_1-phase fraction ratio in the onychin group was higher thanthat in the 10% NCS group(85.2% vs 70.0%,P<0.01),while the S-phase fractionratio in the onychin group was lower than that in 10% NCS group(4.3% vs16.4%,P<0.01).Western blot analysis showed that onychin inhibited Rb phos-phorylation and reduced the expression of cyclin D_1 and cyclin E.The effects ofonychin on proliferation,the cell cycle and the expression of cyclins in VSMCswere similar to those of genistein,an inhibitor of tyrosine kinase.Furthermoreimmunoprecipitation studies showed that both onychin and genistein markedlyinhibited the tyrosine phosphorylation of ERK1/2 induced by 10% NCS.Conclusion:Onychin inhibits the proliferation of VSMCs through G_1 phase cellcycle arrest by decreasing the tyrosine phosphorylation of ERK1/2,and the ex-pression of cyclin D_1 and cyclin E,and sequentially inhibiting Rb phosphorylation. Aim: To investigate the effects of onychin on the proliferation of cultured ratartery vascular smooth muscle cells (VSMCs) in the presence of 10% new-born calf serum (NCS). Methods: Rat VSMCs were incubated with onychin 1-50μmol/L or genistein 10μmol/L in the presence of 10% NCS for 24 h.The prolif-eration of VSMCs was measured by cell counting and MTS/PMS colorimetric assays.Cell cycle progression was evaluated by flow cytometry.Retinoblastoma(Rb)phosphorylation,and expression of cyclin D_1 and cyclin E were measured by Western blot assays. The tyrosine phosphorylation of ERK1/2 was examined by immunoprecipitation techniques using anti-phospho-tyrosine antibodies.Results: The proliferation of VSMCs was periodically significant in the presence of 10% NCS.Onychin reduced the metabolic the metabolic The rate of MTS and the cell number of VSMCs in the presence of 10% NCS in a dose-dependent manner.Flow cytometry analy-sis revealed that the G_1-phase fraction ratio in the onychin group was higher than that in the 10% N. CS group (85.2% vs 70.0%, P<0.01), while the S-phase fraction ratio in the onychin group was lower than that in 10% NCS group (4.3% vs16.4%, P<0.01). That onychin inhibited Rb phos-phorylation and reduced the expression of cyclin D_1 and cyclin E.The effects ofonychin on proliferation,the cell cycle and the expression of cyclins in VSMCswere similar to those of genistein,an inhibitor of tyrosine kinase.Furthermoreimoprecipitation studies showed that Both onychin and genistein markedlyinhibited the tyrosine phosphorylation of ERK1/2 induced by 10% NCS.Conclusion:Onychin inhibits the proliferation of VSMCs through G_1 phase cellcycle arrest by decreasing the tyrosine phosphorylation of ERK1/2, and the ex-pression of cyclin D_1 and Cyclin E, and penta inhibiting Rb phosphorylation.