ABSTRACT
Address correspodence to: Michael J.Quon, Cardiology Branch National Heart, Lung, and Blood Institute National Institutes of Health Building 10, Room 8C-218 10 Center Drive MSC 1755 Bethesda, MD 20892-1755, Tel: (301) 496-6269; Fax: (301) 4021679; Email: quonm@nih.gov
SUMMARY
Vascular endothelium participates in the control of blood flow, vascular tone, and blood pressure by producing the potent vasodilator nitric oxide (NO) in a regulated manner. Endothelial insulin receptors were previously thought to function exclusively as transporters that deliver insulin across the endothelium to target tissues where insulin exerts its biological actions. It is now recognized that signaling by endothelial insulin receptors stimulates production of NO, endothelin, and other vasoactive substances so that endothelial cells themselves may be physiological targets for insulin action. Insulin signaling pathways related to production of NO in endothelial cells contain intriguing similarities to insulin signaling pathways involved with regulation of glucose transport in adipose tissue. Interestingly, although vasodilator actions of insulin are dependent upon production of NO, recent in vivo studies suggest that additional factors may also contribute to hemodynamic actions of insulin. In this chapter, we review recent in vitro and in vivo studies of insulin action in endothelium that support the hypothesis that regulation of blood flow and glucose metabolism are coupled. This interdependence between hemodynamic and metabolic homeostasis may help to explain the frequently observed associations between hypertension and other insulin resistant states such as obesity and diabetes.
