Nitrotyrosine expression is enhanced in aortas from diabetic GK and in GK + AD rats, indicative of increased peroxynitrite formation. Representative aortic sections showing nitrotyrosine staining in control Wistar (A), diabetic GK (B), diabetic GK fed with AD diet (C), Wistar treated with metformin (W + M; D) and diabetic GK rats with normal GK + M (E), and high-fat fed diet GK + AD + M (F) rats treated with metformin. The endothelium is facing up in all layers. Panel G shows quantification of the green fluorescence in the different groups of arteries. Data are mean ± SE. *P < 0.05, ***P < 0.001 versus Wistar group; §P < 0.01, §§§P < 0.001 versus GK control group; φφφP < 0.001 versus GK + AD group.