Spiramine N-6,a C 20 -skeleton diterpenoid alkaloid,was isolated from Spiraea japonica L.f.In this paper,the effects
of
spiramine N-6 were investigated on
platelet aggregation in vitro and in vivo,platelet serotonin release,and on the binding of thrombin-stimulated platelets to neutrophils by use of the methods of Born,Shen,and Hamburger,respectively.The results showed that spiramine N-6 in vitro significantly inhibited platelet activating factor (PAF)-induced platelet aggregation in a concentration-dependent manner while had no influence on platelet aggregation induced by arachidonic acid (AA) or adenosine diphosphate (ADP).The medium inhibitory concentration (IC 50 ) on PAF was 26 μmol/L.Intravenous spiramine N-6 markedly suppressed platelet aggregation induced by ADP,AA,or PAF.Spiramine N-6 also decreased serotonin release from platelets activated by AA and PAF,obtaining the IC 50 values of 64.7 and 33.5 μmol/L.Spiramine N-6 decreased the binding between thrombin-stimulated platelets and neutrophils with an IC 50 of 78.6 μmol/L.It is suggested that spiramine N-6 inhibited platelet aggregation in vitro and in vivo,decreased serotonin release from platelet,and suppressed the binding of activated platelets to neutrophils.