Insulin resistance is thought to be one of the primary pathogenic mechanisms that is responsible for the phenotype and complications associated with type 2 diabetes mellitus (T2DM) and obesity. Insulin is uniquely capable of modifying it's action, because insulin, in addition to the direct effect of enhancing tissue glucose uptake, also modulates the delivery of substrate and insulin by affecting blood flow, especially to skeletal muscle. The vascular effects of insulin are mediated through the release of nitric oxide (NO) which is formed when the enzyme nitric oxide synthase (NOS) catalyzes the conversion of L-arginine to L-citrulline. Both the direct tissue effect, as well as the vascular effect of insulin is blunted in subjects with insulin resistance. The exact mechanisms that induce insulin resistance are not yet clear. We have described insulin resistance in several animal models: 1) Systemic administration of L-NMMA (a competitive inhibitor of NOS) in rats results in hypertension and insulin resistance. 2) Administration of L-NMMA into the lateral cerebral ventricle of rats also results in hypertension and insulin resistance. 3) Mice with targeted disruption of the endothelial as well as neuronal NOS isoforms (eNOS and nNOS respectively) have been described to be hypertensive. We recently demonstrated insulin resistance in both these knockout mice, raising the possibility that NOS activity and NO production may play an important role in regulating insulin action and causing insulin resistance. However, it is unclear if the effect of NO is on the delivery of substrate by regulating blood flow or if it modifies insulin action in the tissues directly. This proposal will address blood blow, glucose uptake in skeletal muscle as well as the insulin signalling pathway in eNOS and nNOS knockout mice, and in rats infused with L-NMMA systemically as well as intracranially. It is designed to test the following hypotheses: 1) NOS activity and NO production play an important role in regulating skeletal muscle blood flow in response to insulin. 2) NOS activity regulates glucose uptake by skeletal muscle. 3) NOS activity modulates insulin action in tissues. Thus the experiments detailed in this application will enable us to understand insulin resistance in greater detail, and help guide the development of future therapeutic strategies. In addition, these experiments will allow the PI to be well trained in research techniques, and together with the career development plan result in the development of an independent research scientist.
| Shankar, R Ravi; Charchar, Fadi J; Eckert, George J et al. (2007) Studies of an association in boys of blood pressure and the Y chromosome. Am J Hypertens 20:27-31 |
| Saha, Chandan; Eckert, George J; Pratt, J Howard et al. (2005) Onset of overweight during childhood and adolescence in relation to race and sex. J Clin Endocrinol Metab 90:2648-52 |
| Shankar, R Ravi; Ferrari, Paolo; Dick, Bernard et al. (2005) Activity of 11beta-hydroxysteroid dehydrogenase type 2 in normotensive blacks and whites. Ethn Dis 15:407-10 |
