許多研究已證實胍類衍生物(guanidine-derivative compound)可能活化咪唑啉第二型受體(imidazoline subtype 2 receptor, I2R)產生降血糖作用，或是活化咪唑啉第三型受體(imidazoline subtype 3 receptor, I3R)促進胰島素的釋放。Canavanine 為Sutherlandia frutescens和苜蓿芽的主要活性成分之ㄧ，且結構中具有胍類結構。故本研究想要探討canavanine是否經由活化imidazoline receptor而具有降血糖作用。在正常大白鼠可觀察到canavanine具有調降血糖的作用。在streptozocin誘導第一型糖尿病大鼠上，canavanine除了使血糖下降以外，同時也可增加-endorphin 的釋放。這兩項作用在預先給予I2R拮抗劑(BU224)後會被抑制。canavanine可經活化I2R達到增加正常大白鼠骨骼肌對葡萄糖的攝取，接著，canavanine可促進C2C12 肌母細胞對葡萄糖的攝入，這項作用可被BU224和amiloride (I2A接受器阻斷劑)所抑制。文獻指出，腺苷酸活化蛋白激酶(AMPK)磷酸化後，可增加第四型葡萄糖轉運蛋白(Glut4)的蛋白表現量，進而可增加對葡萄糖攝入。因次，利用西方點墨法去觀察在給予藥物後，C2C12肌母細胞AMPK的磷酸化及Glut4的蛋白表現。由結果可以看到BU224和amiloride可以抑制canavanine促進的AMPK磷酸化，同時Glut4蛋白的表現量亦可被BU224、amiloride及Compound C (AMPK磷酸化的抑制劑)所抑制。此外，在正常大白鼠中發現canavanine具有促進胰島素釋放的作用。在HIT-T15胰島細胞canavanine也會有促進胰島素分泌的作用，且可被KU 14R (I3接收器阻斷劑)所抑制。最後，利用葡萄糖耐受性試驗、胰島素耐受性試驗及HOMA-IR進行分析得知canavanine不只可以增加葡萄糖的利用率，同時也可增加胰島素敏感性。综合以上結果，canavanine可經由活化I2R以非胰島素依賴的路徑和經由活化I3R以胰島素依賴路徑達到降血糖作用，此也暗示著canavanine有益於治療第一型或第二型的糖尿病。

Several studies have been demonstrated that the guanidine-derivative compound has a potent effect on decreasing the plasma glucose via imidazoline subtype 2 receptor (I2R) or increasing the secretion of insulin via imidazoline subtype 3 receptor (I3R). Canavanine, belongs to one of the guanidine derivatives, is one of the active ingredient extracted from Sutherlandia frutescens and Medicago sativa. The present study aimed to clarify whether canavanine exerted the hypoglycemic effect through activating IR. In normal rats, canavanine decreased the blood glucose in a dose-dependent manner. In streptozotocin-induced diabetic rats, canavanine lowered the plasma glucose and increased -endorphin, which were abolished by pretreatment the rats with BU224 at the dose sufficient to block I2R. Canavanine also dose-dependently increased the glucose uptake in isolated skeletal muscle, which was blocked by BU224. Moreover, we used C2C12 skeletal myoblast cells to verify whether canavanine augmented the glucose uptake ability via I2R. Results showed that canavanine dose-dependently increased the glucose uptake in C2C12 cells, whereas this effect was blocked by both BU224 and amiloride (an I2A blocker). Several studies indicated that the phosphorylated AMPK (pAMPK) raises expression of glucose transporter 4 (Glut4), leading to the increase of glucose uptake. We also employed Western blotting analysis to detect the effect of canavanine on AMPK phosphorylation and Glut4 expression. These results revealed that canavanine enhanced the levels of pAMPK and Glut4 expression in C2C12 cells, which were abolished by BU224, amiloride and compound C (an AMPK inhibitor). Furthermore, canavanine produced an insulinotropic action in normal rats. An increase of insulin release was observed by canavanine in HIT-T15 cells, a pancreatic islet -cell, whereas this effect was blocked by I3R antagonist, KU 14 R. Finally, we also found that canavanine not only increased the ability on glucose utilization but also improved the insulin sensitivity determined by glucose tolerance test, insulin tolerance test and HOMA-IR. Taken together, these results suggested that canavanine produced hypoglycemic action through both I2R in insulin-independent and I3R in insulin-dependent pathways and implicated that it might be beneficial effect for both type 1 and type 2 diabetes.

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