Abstract: ObjectiveTo study the effects of polysaccharide from laminaria(L01)on the expression and secretion of tissue plasminogen activator(t-PA)and plasminogen activator inhibitor-1(PAI-1)stimulated by adrenaline in cultured human umbilical veinendo thelial cell(HUVEC).MethodsWith added adrenaline,six groups of human umbilical veinendothelial cell:line ECV-304 was exposed to different concentrations of polysaccharide of laminaria and cultured for 24,48 and 72 hours respectively in vitro.The levels of t-PA and PAI-1 in cultured supernatants were measured by enzyme-linked immunosorbent assay:RT-PCR was used to detect the expression of t-PA and PAI-1 messenger RNA(mRNA)in HUVEC,and the related products were examined by density scan and half-quantiative analysis after electrophoresis to reflect the variety of transcripition levels.ResultsStimulated by adrenaline,the levels of t-PA and PAI-1 in cultured supernatants increased significantly.But the effect was reduced by different concentrations of L01 after cultured for 24,48 hours,the levels of t-PA decreased siginificantly,but the levels of expression of t-PA mRNA were not siginificantly different all the time.After cultured 48,72h,the level of PAI-1 decreased siginificantly,and the levels of expression of PAI-1 mRNA decreased siginificantly and dose-effect dependently.ConclusionL01 not only has the protective effect on HUEVC,but also increases fibrinolytic activity and facilitate spontaneous thrombolysis.