Aim:To investigate the effect of aspirin on the apoptosis of cultured bovineaortic endothelial cells(BAEC)and the signal pathways involved in this process.Methods:BAEC were cultured and passaged in Dulbecco’s modified Eagle’smedium culture medium.Morphologic changes and quantification of apoptoticcells were determined using fluorescence microscope after staining the cells withHoechst 33258.Cell viability was measured by 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide(MTT)method.DNA fragmentation was visualizedby agarose gel electrophoresis.Phospho-p38 mitogen-activated protein kinase(MAPK)expression was detected by Western blotting.Results:Aspirin at lowconcentrations from 1×10~(-10)mol/L to 1×10~(-8)mol/L decreased the apoptosis andp38 MAPK pbosphorylation induced by H_2O_2 in BAEC,while high doses of aspi-rin(1×10~(-7)-1×10~(-4)mol/L)induced typical apoptotic changes in BAEC and stimu-lated the expression of phospho-p38 MAPK in a concentration-dependent manner.SB203580,a specific p38 MAPK inhibitor,blocked such effects.Conclusion:Aspirin exhibits a biphasic effect on the apoptosis in BAEC,reducing apoptosisat low concentration and inducing apoptosis at high concentration,p38 MAPKmay be an important signal molecule mediating the effects of aspirin. Aim: To investigate the effect of aspirin on the apoptosis of cultured bovineaortic endothelial cells (BAEC) and the signal pathways involved in this process. Methods: BAEC were cultured and passaged in Dulbecco’s modified Eagle’s medium culture medium. Morphologic changes and quantification of apoptotic cells were determined using fluorescence microscope after staining the cells with Hoechst 33258. Cell viability was measured by 3- [4,5-dimethylthiazol-2-yl] -2,5-diphenyltetrazolium bromide (MTT) method. DNA fragmentation was visualized by agarose gel electrophoresis. Phospho-p38 mitogen-activated protein kinase (MAPK) expression was detected by Western blotting. Results: Aspirin at low concentrations from 1 × 10 -10 mol / L to 1 × 10 -8 mol / L decreased the apoptosis rate andp38 MAPK pbosphorylation induced by H_2O_2 in BAEC, while high doses of aspi-rin (1 × 10 -7 -1 × 10 -4 mol / L) induced typical apoptotic changes in BAEC and stimu-lated the expression of phospho-p38 MAPK in a concentration-dependent manner.SB2035 80, a specific p38 MAPK inhibitor, blocked such effects. Conlusion: Aspirin exhibits a biphasic effect on the apoptosis in BAEC, reducing apoptosisat low concentration and inducing apoptosis at high concentration, p38 MAPK can be important signal molecule mediating the effects of aspirin.