Oxygen radicals: effects on intestinal vascular permeability

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Abstract
There is now a considerable amount of evidence in the liberature implicating oxygen-derived free radicals in the vascular permeability changes associated with intestinal ischemia. To directly assess the effects of oxygen radicals on vascular permeability, hypoxanthine-xanthine oxidase, an enzyme-substrate system known to generate oxygen free radicals, was infused into the arterial supply of autoperfused segments of cat ileum. The osmotic reflection coefficient (.sigma.d) of intestinal capillaries to total plasma proteins was estimated from the steadystate relationship between lymph-to-plasma total protein concentration ratio and lymph flow. Intra-arterial infusion of hypoxanthine-xanthine oxidase reduced .sigma.d fram a control value of 0.92 to 0.66, indicating an increased vascular permeability. This increase in vascular permeability was significantly attenuated by the addition of superoxide dismutase (dd = 0.86), a specific scavenger of superoxide anion (O-2), or dimethylsulfoxide (.sigma.d = 0.83), the hydroxyl radical (OH.cntdot.) scavenger, to the infusate. Oxygen-derived free radicals, generated by the reaction of hypoxanthine with xanthine oxidase, increase intestinal vascular permeability to an extent comparable with that observed in preparations subjected to 1 h of ischemia.

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