Effect of insulin on human aortic endothelial nitric oxide synthase.

It has recently been shown that insulin induces vasodilation in human arteries and veins in vivo. This effect of insulin has been shown to be a direct one on the human vein. In view of these observations and the fact that insulin-induced vasodilation is impaired in insulin-resistant states like type 2 diabetes and obesity, we have investigated the hypothesis that insulin may induce the expression of endothelial nitric oxide synthase (e-NOS) in endothelial cells grown from human aortae (HAECs), human lower-limb veins, and human umbilical veins (HUVECs), and microvascular endothelial cells (MVECs) from human adipose tissue. The expression of e-NOS was maximal in HAECs, and therefore, further experiments were performed on these cells. When cells reached 90% confluence, they were induced with different concentrations of insulin (0, 25, 100, and 1,000 microU/mL) for 6 days. The cells were homogenized and e-NOS expression was examined by Western blotting. A dose-dependent induction by insulin of e-NOS in the endothelial cells was clearly demonstrated. There was no detectable level of the inducible NOS isoform (i-NOS), and this effect of insulin was independent of cell proliferation. We conclude that insulin induces a dose-dependent induction of e-NOS in human aortic cells (and possibly arterial/endothelial cells), and this effect may contribute to the overall vasodilatory effect of insulin.