嗎啡強化活化劑引起血小板凝集反應的機轉探討

嗎啡最早在十九世紀初被發現具有強力的止痛效果，用來緩解癌症末期病患的疼痛，且對處理 某些重大的疾病、創傷及外科手術是必須的。至於嗎啡對人體血小板的影響如何？其機轉又為何？

近幾年來卻少有人討論，本篇論文主要的研究目的是詳細的進一步探討嗎啡作用在血小板上的機制。

在人體的血小板懸浮中，發現 morphine 能隨著濃度的增加而有效的強化由 collagen (1 g/ml) 、 U4 6619 (0.5 M)  所引起的血小板凝集及 ATP 釋放反應。 morpine (1, 5 M)  能依劑量相關性的方式 (dose-dependent) ，強化不同活化劑所引起的血小板凝集反應。另外， morphine 強化 collagen 所引 起的 phosphoinositides (PI) 的分解，同時亦可促進 collagen 所引起的血小板細胞內 pH 值上升與鈣 離子的增加及 thromboxaneB2 的形成。再者利用偵測血小板內 prostaglandin E2 的含量來代表 cycloo xygenase 活性時，發現 morphine 對 cyclooxygenase 的活性並沒有影響。

接下來，利用 yohimbine (0.1 M)  會和血小板細胞膜上的 2-adrenoceptors 結合的特性，發現 morp hine 在 Yohimbine 的存在下，無法強化 collagen (2 g/ml)  所造成的血小板凝集效果。這個實驗結果 可能和 morphine 作用在血小板的 2-adrenoceptors 有關。

另一方面，嗎啡無法影響 FITC-triflavin 與血小板表面之 glycoprotein IIb/IIIa complex 的結合。 Trifl avin 是由 Trimeresurus flavoviridis 蛇毒中純化的的單鏈 peptide, 對血小板細胞膜的 GP IIb/IIIa 受體 具有專一性的拮抗作用。 Morphine (1, 5 M)  能抑制血小板內由 prostaglandin E1 (10 M)  所引起 的 cyclic AMP 的含量；另外利用 chemiluminesence 的方法進一步探討 morphine 對血小板中 NO 的 影響，實驗結果發現 morphine 單獨存在下並不會增加 NO 的濃度。

綜合以上的實驗結果，發現 morphine 作用在血小板的機制可能為透過 2-adrenoceptors 而抑制細胞 內 cyclic AMP 的增加，並且增加細胞內鈣離子的釋放，經由 arachidonic acid 的路徑，造成 thrombo xane B2 的含量增加，最後造成強化血小板凝集的結果。

嗎啡強化活化劑引起血小板凝集反應的機轉探討

Mechanisms of morphine potentiated agonist- induced platelet aggregation in human platelets

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The discovery of pharmacological activity of morphine early in the 19th century and the demonstration of its potent analgesi c properties. Morphine had been used to relax the pain of cancer patients on the last phase , and dealed with some serious dis eases 、 trauma and surgery was needed. However, how the influence of morphine on wash human platelets, and what are th e mechanisms involved in this influence, it still remains unclear. Recently the subject had not been discussed widely. The ai m of this thesis is to further investigate the detailed mechanisms of morphine on human platelets.

In our studies, we found that morphine (1, 5 M) dose—dependently potentiated platelet aggeregation and ATP release by c  ollagen (1 g/ml) and U46619 (0.5   in human platelet suspensions. Morphine (5 M) potentiated [3H inositol monopho  

sphate formation stimulated by collagen (5 g/ml) in [3H myoinositol loaded platelets. Furthermore, morphine also potentia  

ted [Ca2+]i mobilization in human platelet suspensions stimulated by collagen (1 g/ml). At the same dose, morphine signifi  cantly potentiated thromboxane B2 formation of collagen-activated platelets.

Consequently, we measured prostagladinE2 formation as an index of cyclooxygenase activity. We found that morphine had no significant effect on cyclooxygenase activity, and found it did not potentiate collagen-induced platelet aggregation in the presence of yohimbine. According to these results, we found the effect of morphine on human platelets may be mediated via activation of  adrenoceptors.

On the other hand, morphine (1, 5  ) inhibited prostaglandin E1 (10  induced cyclic AMP increase in human platelet s. We examined this potentiation involved in platelet signal transduction system such as Na/H pump in human platelet suspe   nsions. In contrast, morphine did not significantly increase nitrate formation in human platelets.

Moreover, we found morphine did not influence the binding of FITC-triflavin to platelet glycoprotein IIb/IIIa complex. Trifl avin, an Arg-Gly-Asp-containing antiplatelet peptide, was purified from Trimeresurus flavoviridis snake venom.

Measurement of the platelet membrane fluidity, we found that morphine did not significantly affect the platelet membrane fl uidity diphenylhexatriene (DPH)-loaded platelets .

Based on the above observations, we suggested that morphine may bind to  adrenoceptors in human platelets, resulting i n inhibition of cyclic AMP formation and concurrently increased intracellular Ca2+, resulting in activation of phospholipase A2 , and increased formation of thromboxane A2 formation, and potentiation of platelet aggregation.