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Cardiovascular function in animal models of metabolic syndrome and type 2 diabetes : the role of inducible nitric oxide synthase (iNOS) Song, Dongzhe

Abstract

Activation of inducible nitric oxide synthase (iNOS) and oxidative stress have been shown to be associated with compromised cardiovascular function in streptozotocin (STZ)-induced type 1 diabetes. The aim of the project is to investigate cardiovascular abnormalities in a rat model of type 2 diabetes (Zucker diabetes fatty or ZDF rats) and two models of metabolic syndrome (fructose-fed rats and Zucker obese rats), and to provide direct evidence linking iNOS and oxidative stress to abnormal cardiovascular function in these disorders. Blood pressure, cardiac contractility, cardiac index, regional flow, vascular resistance and venous tone were measured in diseased as well as normal rats. Biochemical analyses such as activities of iNOS, immunostaining of iNOS and western-blot analysis of iNOS in the heart tissue were carried out. The results showed that cardiac contractile response to dobutamine was compromised in the ZDF rats, and this was associated with increased myocardial protein expression as well as activity of iNOS. The formation of peroxynitrite was increased in the heart tissue of the ZDF rats. Selective inhibition of iNOS by 1400W (N-3-aminomethyl-benzyl-acetamidine) did not alter responses to dobutamine in the control rats, but augmented the contractile effects of dobutamine in the diabetic rats. The regional blood flow was altered in the ZDF rats, and iNOS played a negligible role in regulating regional flow in the ZDF rats. Although venous response to noradrenaline was also altered in the Zucker obese rats, NOS may not be involved in venous tone regulation. Anti-oxidative treatment with N-acetylcysteine inhibited the development of insulin resistance, blood pressure elevation and the increase of 8-isoprostane formation in the fructose-fed rats. We conclude that heart function is compromised and regional blood flow is altered in the ZDF rats. Activation of iNOS plays an important role in suppressing heart dysfunction but does not affect regional blood flow. In Zucker obese rats with metabolic syndrome, iNOS may not be involved in changes of venous function. Oxidative stress is associated with both abnormality of heart dysfunction in type 2 diabetes (by formation of peroxynitrite due to iNOS activation) and development of hypertension and insulin resistance in metabolic syndrome.

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