Four antiplatelet components were isolated from Arnebia euchroma. They inhibited the aggregation of washed rabbit platelets caused by collagen, arachidonic acid, platelet-activating factor, ADP, or thrombin. The potency of inhibiting collagen-induced platelet aggregation is in the following order: acetylshikonin (IC50 = 2.1 microM), teracrylshikonin (2.8 microM), beta, beta-dimethylacrylshikonin (4.2 microM), and shikonin (10.7 microM). In rat aorta, acetylshikonin and shikonin inhibited high potassium and norepinephrine-induced contractions, while beta, beta-dimethylacrylshikonin and teracrylshikonin potentiated the phasic contraction caused by norepinephrine.
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Chang et al. (1993) studied this question.