Molecular and physiologic actions of insulin related to production of nitric oxide in vascular endothelium.

Insulin has important vascular actions that regulate blood flow, in addition to its classical actions to coordinate glucose homeostasis. Insulin-stimulated production of nitric oxide in vascular endothelium results in capillary recruitment and vasodilation that diverts and increases blood flow to skeletal muscle and consequently increases glucose disposal. Thus, vascular actions of insulin may be essential for coupling hemodynamic and metabolic homeostasis. A complete biochemical signaling pathway linking the insulin receptor to activation of endothelial nitric oxide synthase in vascular endothelium has recently been elucidated. Moreover, the time course and dose response for capillary recruitment in response to physiologic concentrations of insulin parallels that of insulin-mediated glucose uptake in vivo. Taken together, these observations suggest a molecular mechanism that may help to explain how insulin resistance contributes to cardiovascular components of the metabolic syndrome and vascular complications of diabetes.