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Using turbidimetry and electronmicroscopy

we examined the effects oftetrandrine （Tet） on the aggregation and morphological changes of rabbit platelets.It wasfound that Tet could markedly inhibit the platelet aggregation induced by ADP

collagenand arachidonic acid （AA） in a dose-dependent manner.The IC

50

（50% inhibitoryconcentration） was 38.9

30.3 and 44.3μg/ml respectively.The platelets pretreated with Tetcould not be activated by collagen

their morphological changes and granule release didn’toccur and their normal structure was well preserved.In addition

dipyridamole couldenhance the inhibition of Tet on platelet aggregation

while increased extracellular calciumcould weaken this inhibition.