To understand the relationship between hypertension and insulin resistance we are studying insulin signal transduction pathways related to nitric oxide production in vascular endothelium. Human forearm blood flow studies suggest that physiological concentrations of insulin can cause vasodilation of small vessels via the production of nitric oxide by endothelial cells. Furthermore, the degree of insulin sensitivity exhibited for this vasodilatory response is positively correlated with insulin sensitivity for glucose uptake. This suggests that insulin signaling pathways may be related to nitric oxide production in vascular endothelium. Thus, insulin resistance may contribute to the pathogenesis of hypertension under some conditions. We recently obtained a nitric oxide meter that is capable of directly measuring nitric oxide at nanomolar concentrations. We are using this device to characterize the insulin response of human umbilical vein endothelial cells (HUVEC) in primary culture. In addition, we have developed a novel method for transfecting endothelial cells in primary culture and selecting the transfected cells using a fluorescently activated cell sorter. By overexpressing wild-type, constitutively active, or dominant inhibitory forms of various signaling molecules, we will be able to elucidate the molecular signal transduction pathways utilized in insulin-stimulated production of nitric oxide. We are also investigating potential mechanisms whereby insulin may regulate the activity and expression of endothelial nitric oxide synthase.