ABSTRACT
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 immunosorbent 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 blotting.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.Treatment 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.
ABSTRACT
Sheng-Mai-San (SMS), a well-known Chinese medicinal plant formula, is widely used for the treatment of cardiac diseases characterized by deficiency of Qi and Yin syndrome. A mouse chronic intermittent hypoxia (CIH) model was established to mimic the primary clinical features of deficiency of Qi and Yin syndrome. Mice experienced CIH for 28 days (nadir 7% to peak 8% oxygen, 20 min per day), resulting in left ventricle (LV) dysfunction and structure abnormalities. After administration of SMS (0.55, 1.1, and 5.5 g·kg(-1)·d(-1)) for four weeks, improved cardiac function was observed, as indicated by the increase in the ejection fraction from the LV on echocardiography. SMS also preserved the structural integrity of the LV against eccentric hypotrophy, tissue vacuolization, and mitochondrial injury as measured by histology, electron microscopy, and ultrasound assessments. Mechanistically, the antioxidant effects of SMS were demonstrated; SMS was able to suppress mitochondrial apoptosis as indicated by the reduction of several pro-apoptotic factors (Bax, cytochrome c, and cleaved caspase-3) and up-regulation of the anti-apoptosis factor Bcl-2. In conclusion, these results demonstrate that SMS treatment can protect the structure and function of the LV and that the protective effects of this formula are associated with the regulation of the mitochondrial apoptosis pathway.