摘要
黃芩(Scutellariae Radix) 為Labiatae屬Scutellaria baicalensis Georgi之根除去周皮之生藥。在「神農本草經」上列為草部中品，並記載有清熱燥濕、降火解毒及安胎等功用。近來黃芩也被發現有抗發炎和抗氧化的作用，因此本研究探討黃芩水抽取物及其4種主要flavonids成分─ baicalin、baicalein、oroxylin A、wogonin對於人類血小板凝集作用之抑制活性測定結果如下：（1）黃芩水抽取物對collagen (10 μg/ml)、U46619 (2 μM) 所引起血小板凝集之反應具有劑量依存性(dose-dependent)，其IC50分別為73.5、73.8 μg/ml。（2）Baicalin、baicalein對collagen (10 μg/ml)、U46619 (2 μM)、ADP (10 μM)所引起血小板凝集之反應均具有劑量依存性(dose-dependent)，其IC50分別為74.5、35.2、61.5 μg/ml及34.5、37.7、65.8 μg/ml；但對於collagen引起的TxB2生成卻無抑制作用；另外對血小板懸浮液也無提昇cAMP、cGMP和NO的生成。由上述結果顯示：baicalin和baicalein是藉由抑制common pathway (如Ca2+ mobilization或PI turnover )而產生抗血小板凝集作用。（3）Oroxylin A對U46619 (2 μM) 所引起的血小板凝集反應之抑制亦具有濃度依存性，其IC50為45 μg/ml，同時對由collagen引起的TxB2生成(4.9 ± 0.6 pg，control 21.1 ± 0.5 pg)亦有抑制。此外oroxylin A也可以提高NO的生成(8.5 ± 0.4 μM，control 2.6 ± 0.1 μM)。但是對於cAMP、cGMP則沒有作用。因此推測oroxylin A抑制血小板凝集之機制是經由抑制TxA2的生合成及誘生NO而來抑制血小板的凝集。（4）Wogonin對collagen (10 μg/ml)、U46619 (2 μM) 所引起的血小板凝集反應中呈現劑量依存性，其IC50為59.1、45 μg/ml，並抑制由collagen所引起的TxB2之生成(6.8 ± 0.5 pg，control 21.1 ± 0.5 pg)。此外wogonin也提升NO的生成(15.5 ±1.2 μM，control 2.6 ± 0.1 μM)。但是對於cAMP、cGMP皆沒有提高生成的作用。另外在Schild analysis和competitive binding sites測定結果中，wogonin於一定濃度時U46619有隨著濃度的增加而有更大的反應(maximum response)，且隨著wogonin濃度增加，U46619的劑量有向右移動(shift to the right)的現象。進一步以Schild plot計算pA2和pA10 values值分別為5.95及4.50，顯示wogonin與U46619作用在相同的部位，因此會與作用劑(U46619)競爭相同的部位。從以上結果顯示，wogonin對血小板的抑制作用可能是是經由與TxA2競爭receptors及誘生NO之產生而抑制血小板的凝集。 綜合以上結果顯示，黃芩水抽取物具有對人類血小板凝集之抑制作用，而baicalin、baicalein、oroxylin A、wogonin為其活性主成分。
並列摘要
Scutellariae Radix, the roots of Scutellaria baicalensis Georgi (Labiatae) has been demonstrated that the therapeutic effects on treatment of bloodless in Chinese medicinal books. However, the action mechanism of Scutellariae Radix on blood function is undefined. Therefore, study the functions of Scutellariae Radix on platelet aggregation was performed in this project. Baicalin、baicalein、oroxylin A and wogonin are the major compounds of Scuteiilaire Radix and several biological activities have been demonstrated in these compounds including antioxidant activity and anti-inflammation. In order to study the activities from Scutellariae Radix on platelet aggregation, these four compounds isolated from Scutellariae Radix were used to investigate their inhibitory effects on platelet aggregation induced by collagen, U46619 or ADP in human platelet-rich plasma. The results showed that these four polyphenolic compounds showed the significant inhibition on collagen-, U46619- or ADP-induced aggregation. The IC50 values of baicalin, baicalein and wogonin are 74.5, 34.5, >100, 59.1 μg/ml in the collagen-induced aggregation, and 35.2, 37.7, 45, 45 μg/ml in the U46619-induced aggregation, respectively. As the same part of experiment, both baicalin and baicalein also showed the obvious dose-dependent inhibition of ADP-induced platelet aggregation, and the IC50 values are 61.5 and 65.8 μg/ml, respectively. These data provided evidences that Scutellariae radix inhibits stimulators induced platelet aggregation. Nitric oxide (NO) and TxB2 have been implicated to play as modulators in the process of platelet aggregation. Upon oroxylin A and wogonin treated platelet, NO production was significantly increased to 8.5 ± 0.4 and 15.5 ± 1.2 μM, respectively, as compared with the controlled group (2.6 ± 0.1 μM). A binding site for TxA2 antagonist wogonin to PRP was studied. Wogonin competitively antagonized aggregation of PRP by the TxA2 mimetic U46619. A Schild analysis of the pharmacology study revealed a pA2 of 3.90 and pA10 of 5.01. It suggests that this high-affinity binding sites is the site responsible for inhibition of aggregation induced by U46619. These data provided evidences that Scutellariae Radix inhibits stimulators induced platelet aggregation.