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Objective— Angiotensin II (AII) has been shown to increase endothelial NAD(P)H oxidase activity, which is a source of superoxide anion that in turn may induce the formation of peroxynitrite. Estrogen (E₂) has been reported to have vascular protective effects. In this study, we hypothesized that E₂ reduces the AII-induced expression of NAD(P)H oxidase and peroxynitrite in endothelial cells.

Methods and Results— Endothelial cells were cultured and stimulated with AII in the absence or presence of E₂. Western blots were used to assess nitric oxide synthase (NOS) and NAD(P)H oxidase expression. Immunofluorescence of nitrotyrosine provided evidence of peroxynitrite formation. Our data indicate that AII increased the expression of endothelial NOS, inducible NOS, and NAD(P)H oxidase in a dose-dependent manner, which was attenuated by incubation with either E₂, superoxide dismutase, or the AII type 1 …