['Fish oil has been shown to improve blood pressure (BP) in some disease states by an unknown mechanism. We tested the ability of fish oil to prevent vascular dysfunction in fructose-fed rats, a model of insulin resistance and hypertension.', 'Rats were placed on three diets: 1) regular rat diet (control); 2) diet containing 60% fructose (FFR); or 3) diet containing 60% fructose and 4.4% fish oil (FFR+FO). After 8 weeks, blood, heart, aorta, and mesenteric artery tissue were collected from each animal. Secondary branch segments of mesenteric arteries were isolated for vascular reactivity studies.', 'Systolic BP increased significantly in the FFR but was reduced to control levels by the addition of fish oil to the diet. In the mesenteric artery segments from FFR, the dose-response curves to acetylcholine were significantly shifted to the right compared with those of control rats and rats on the fish oil diet. Expression of endothelial nitric oxide synthase (eNOS) protein and mRNA was reduced in the FFR aortas and hearts, and this reduction was reversed by the fish oil. Dietary fish oil prevented the hyperlipidemia that occurred in the FFR but did not prevent hyperinsulinemia. Plasma concentrations of hydrogen peroxide, 8-isoprostane, and monocyte chemoattractant protein-1 were significantly elevated in the FFR and were significantly lower in the FFR treated with fish oil.'] Does dietary fish oil prevent vascular dysfunction and oxidative stress in hyperinsulinemic rats?