A single herb can contain multiple constituents with diverse bioactivities. We found\nthat the extract of Citrus unshiu peel (CUP), induced abnormal vasoconstriction responses on\nthe freshly isolated rat aortic rings in vitro. CUP stimulated the vasoconstriction alone, and it\nsuppressed the phenylephrine-stimulated vasoconstriction. We studied the reasons behind this\nabnormal vasoconstriction pattern. Major constituents of CUP were determined and evaluated for\ntheir vaso-activities. Notably, synephrine, a contractile agonist, and nobiletin, newly identified to\nhave anti-contractile activity co-existed in CUP. Synephrine and nobiletin competitively blocked\nor activated the same contractile targets resulting in contradicting and abnormal vasoconstriction\nresponses. Accordingly, the vasoconstriction pattern varies significantly depending on the relative\ncontents of synephrine and nobiletin in CUP. Interestingly, this response pattern could be observed\nwith another plant extract, Acorus gramineus Sol. Collectively, we demonstrated that active ingredients\nwith contradicting bioactivities could co-exist in a single plant extract, interact and produce abnormal\nresponse patterns in bioassay, which would give an important insight into the interpretation of\nunusual activity patterns induced by plant extracts.
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