Endothelium-specific activation of NAD(P)H oxidase in aortas of exogenously hyperinsulinemic rats

To examine the effects of chronic hyperinsulinemia on vascular tissues, we examined the production of superoxide anion (O-2(-)) in the aortic tissues of control and exogenously hyperinsulinemic rats performed by the implantat ion of an insulin pellet for 4 wk. O-2(-) production by aortic segments fro m hyperinsulinemic rats was 2.4-fold (lucigenin chemiluminescence method) a nd 1.7-fold (cytochrome c method) of that of control rats without any diffe rences in O-2(-) degrading activities in aortic tissues, respectively (P < 0.025). The increment was completely abolished in the presence of either 10 0 mu mol/l apocynin (an inhibitor of NADPH oxidase) or 10 mu mol/l diphenyl eneiodonium (an inhibitor of flavin-containing enzyme) and was exclusively endothelium dependent. Consistently, NAD(P)H oxidase activities in endothel ial homogenate in hyperinsulinemic rats were dose dependently stimulated ab ove the values of control rats, although these activities in nonendothelial homogenate were not significantly stimulated by insulin. Furthermore, an i nsulin effect was also demonstrated 1 h after exposing aortic tissues to in sulin. These results indicate that O-2(-) production specifically increases in endothelium of aortic tissues in chronic hyperinsulinemic rats through the activation of NAD(P)H oxidase.