内源性一氧化氮合酶抑制物在糖尿病大鼠勃起功能障碍中的作用

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)在糖尿病大鼠勃起功能障碍中的作用及其机制。方法:采用高脂饲养加小剂量链脲佐菌素腹腔注射诱导8周病程的2型糖尿病大鼠模型;麻醉下分离大鼠阴茎海绵体,用器官浴槽方法检测海绵体对乙酰胆碱的内皮依赖性舒张反应以反映其勃起功能;检测血清ADMA含量;检测海绵体组织NOS活性及一氧化氮(NO)和环磷酸鸟苷(c GMP)含量;用Western blot检测海绵体ADMA信号通路蛋白和磷酸二酯酶5(PDE5)的表达;检测超氧化物歧化酶活性和脂质过氧化产物丙二醛含量以评价氧化应激。结果:糖尿病大鼠血糖升高,胰岛素敏感性降低,表明糖尿病大鼠模型建立成功;与正常对照组比较,糖尿病大鼠海绵体舒张功能明显降低,血清ADMA浓度升高,海绵体组织NOS活性及NO和c GMP含量降低,ADMA生成酶蛋白精氨酸甲基转移酶1表达上调,ADMA代谢酶二甲基精氨酸二甲胺水解酶1、2及ADMA靶酶内皮型NOS和神经元型NOS表达下调,PDE5蛋白表达上调,氧化应激增加;体外用ADMA孵育正常大鼠离体海绵体,亦可产生与糖尿病大鼠海绵体相似的舒张功能障碍及NO和c GMP含量减少。结论:内源性NOS抑制物ADMA蓄积是导致糖尿病大鼠勃起功能障碍的重要原因,其机制可能与减少NO生成、增加氧化应激有关。

Role of endogenous nitric oxide synthase inhibitor in erectile dysfunction of diabetic rats

AIM: To investigate the role of nitric oxide synthase (NOS) inhibitor asymmetric dimethylarginine (ADMA) in erectile dysfunction of diabetic rats.METHODS: Type 2 diabetic rat model was established by 4 weeks of high-fat diet plus a single intraperitoneal injection of streptozotocin and continued high-fat diet feeding for 8 weeks. Corpus cavernosum was isolated from the rats under anesthetization, and the endothelium-dependent relaxation response to acetylcholine (ACh) was tested in an organ chamber to reflect erectile function. The level of ADMA in serum was detected. The NOS activity, nitric oxide (NO) content and cyclic guanosine monophosphate (cGMP) content in corpus cavernosum were measured. The protein expression of ADMA-NOS-NO pathway-related molecules and phosphodiesteras 5 (PDE5) in the corpus cavernosum was detected by Western blot. Superoxide dismutase activity and malondialdehyde content were analyzed to evaluate oxidative stress.RESULTS: Elevated blood glucose and lowered insulin sensitivity were observed in the diabe-tic rats, indicating that type 2 diabetic rat model was successfully established. Compared with control group, the relaxation response to ACh of corpus cavernosum from diabetic rats was significantly decreased, which was accompanied with the elevation of serum ADMA level and reduction of NOS activity, NO content and cGMP content in the corpus cavernosum. The protein expression of ADMA-generating enzyme protein arginine methyltransferase 1 was up-regulated, while ADMA-metabolic enzymes dimethylarginine dimethylaminohydrolases 1 and 2, and ADMA-targeting enzymes endothelial NOS and neuronal NOS were down-regulated. The protein expression of PDE5 was up-regulated, accompanied with an increase in oxidative stress in the corpus cavernosum of diabetic rats. Incubation of isolated corpus cavernosum from normal rats with NOS inhibitor ADMA induced the similar relaxation dysfunction of corpus cavernosum response to ACh and decreased NO and cGMP contents in diabetic rats.CONCLUSION: Elevated endogenous NOS inhibitor ADMA plays an important role in erectile dysfunction of diabetic rats. The underlying mechanism may be related to the reduction of NO production and the increase in oxidative stress.