一氧化氮合酶抑制物在糖尿病大鼠骨骼肌收缩功能损害中的作用

Role of nitric oxide synthase inhibitor in the skeletal muscle contractile dysfunction of type 2 diabetic rats

目的探讨内源性一氧化氮合酶（NOS）抑制物非对称性二甲基精氨酸（ADMA）在糖尿病大鼠骨骼肌收缩功能障碍中的作用及其机制，并观察一氧化氮（NO）合成前体L-精氨酸的治疗作用。方法采用高脂饲养和小剂量链脲佐菌素（30mg／kg）一次性腹腔注射制备8周2型糖尿病大鼠，用电刺激法测定比目鱼肌（SOL）和趾长伸肌（EDL）的单次收缩和强直收缩张力以反映骨骼肌收缩功能；用ELISA检测骨骼肌ADMA含量，用比色法测定二甲基精氨酸二甲胺水解酶（DDAH）和NOS活性以及NO含量，用Western blotting检测ADMA生成酶精氨酸甲基转移酶1（PRMT1）和ADMA代谢酶DDAH以及NOS蛋白表达以反映PRMT／ADMA／DDAH／NOS／NO通路变化；测定大鼠口服糖耐量和胰岛素受体底物1（IRS一1）和蛋白激酶B（Akt）磷酸化水平及葡萄糖转运体4（Glut4）膜转运等以反映胰岛素抵抗。结果与正常对照组比较，糖尿病组大鼠SOL和EDL对电刺激的单次和强直收缩张力均明显降低（P〈0．01），提示骨骼肌收缩功能损害；并伴有骨骼肌组织ADMA含量增加（P〈0．05）、DDAH和NOS活性降低、NO含量减少（P〈0．01）、PRMT1蛋白表达上调以及DDAH、eNOS和nNOS蛋白下调（P〈0．05）。糖尿病组大鼠口服糖耐量降低，骨骼肌IRS一1和Akt蛋白磷酸化水平降低，Glut4膜转位减少（P〈0．05）。经L-精氨酸灌胃治疗8周后明显改善糖尿病大鼠骨骼肌收缩功能损害，纠正ADMA信号通路紊乱和胰岛素抵抗。结论糖尿病大鼠内源性NOS抑制物ADMA蓄积与骨骼肌收缩功能损害密切相关，其机制可能与促进胰岛素抵抗有关。

Objective To investigate the role of endogenous nitric oxide synthase （NOS） inhibitor asymmetric dimethylarginine （ADMA） in the contractile dysfunction of skeletal muscle in diabetic rats and on which the therapeutic effects of L-Arginine. Methods Type 2 diabetic rats were induced by high fat diet and a single intraperitoneal injection of streptozotocin （STZ, 30 mg/kg） , followed by high fat diet for 8 weeks. Specific twicth tension and specific tetanic tension of soleus （SOL） and extensor digitorum longus （EDL） isolated from control and diabetic rats were detected by electric stimulation to reflect contractile function of skeletal muscle. ADMA content of skeletal muscle was analyzed by enzyme linked immunosor- bent assay （ ELISA）, and activities of dimethylarginie dimethylaminohydrolase （DDAH） and NOS, NO content were measured by colorimetry. The protein expression of ADMA synthetase protein arginine methyl transferase 1 （PRMT1） and ADMA hydrolase DDAH and NOS were determined detected by Western blott-ing. Oral glucose tolerance test and protein expressions of phosphorylated insulin receptor substrate 1 （p-IRS-1） and protein kinase B （p-Akt） as well as the membrane transportation of glucose transporter 4 （Glut4） were measured to reflect insulin resistance. Results In comparison with control rats, specific twicth tension and tetanic tension of SOL and EDL in diabetic rats were significantly decreased （P 〈 0. 01 ）, indicating the contractile dysfunction. Increased ADMA content （P 〈 0. 05 ）, decreased DDAH and NOS activities as well as NO content （P 〈 0. 01 ） in comparison with up-regulated protein expression of PRMT1 and down-regulated protein expression of DDAH, endothelial NOS （eNOS） and neuronal NOS （nNOS） （ P 〈 0. 05 ） were observed in the skeletal muscle of diabetic rats compared to control rats, indicating that the pathway of PRMT1/ADMA/DDAH/ NOS/NO was disordered in the skeletal muscle of diabetic rats.Furthermore, the glucose tolerance, both IRS-1 and Akt protein phosphorylation as well as the membrane translocation of Glut4 were decreased （P 〈 0. 05）, indicating the insulin resistance in diabetic rats. Treat- ment with L-Arginine for 8 weeks not only significantly improved the contractile dysfunction but also reversed the disorder of ADMA signaling pathway and insulin resistance in skeletal muscle of diabetic rats compared to untreated diabetic rats. Conclusions The accumulation of endogenous NOS inhibitor ADMA contributes to the contractile dysfunction of skeletal muscle in diabetic rats, the underlying mechanism may be related to insulin resistance.