Regulation of endothelial constitutive nitric oxide synthase gene expression in endothelial cells and in vivo A specific vascular action of insulin

Background-The vasodilatory effect of insulin can be acute or increase with time from 1 to 7 hours, suggesting that insulin may enhance the expression of endothelial nitric oxide synthase (eNOS) in endothelial cells. The obje ctive of the present study was to characterize the extent and signaling pat hways by which insulin regulates the expression of eNOS in endothelial cell s and vascular tissues. Methods and Results-Physiological concentrations of insulin (10(-10) to 10( -7) mmol/L) increased the levels of eNOS mRNA, protein, and activity by 2-f old after 7 to 8 hours of incubation in cultured bovine aortic endothelial cells. Insulin enhanced eNOS gene expression in microvessels isolated from Zucker lean rats but not from insulin-resistant Zucker fatty rats. Inhibito rs of phosphatidylinositol-3 kinase (PI-3 kinase) decreased the effect of i nsulin on eNOS gene expression, but a general protein kinase C (PKC) inhibi tor, GF109203X or PKC beta isoform inhibitor, LY333531 enhanced eNOS expres sion. In contrast, PKC activators inhibited both the activation by insulin of PI-3 kinase and eNOS mRNA levels. Overexpression of PKC beta isoform in endothelial cells inhibited the stimulation by insulin of eNOS expression a nd PI-3 kinase activities in parallel. Conclusions-Insulin can regulate the expression of eNOS gene, mediated by t he activation of PI-3 kinase, in endothelial cells and microvessels. Thus, insulin may chronically modulate vascular tone. The activation of PKC in th e vascular tissues as in insulin resistance and diabetes may inhibit PI-3 k inase activity and eNOS expression and may lead to endothelial dysfunctions in these pathological states.