Hyperbaric oxygen reduces the progression and accelerates the regression of atherosclerosis in rabbits

We studied the effect of hyperbaric oxygen (HBO) treatment on the extent of diet-induced accumulation of lipid oxidation products in rabbit plasma and tissues, on plasma paraoxonase activity, and on the extent of progression and regression of atherosclerotic lesions in the rabbit aorta. HBO treatmen t of cholesterol-fed rabbits dramatically reduces the development of arteri al lesions despite having little or no effect on plasma or individual lipop rotein cholesterol concentrations, Compared with no treatment in cholestero l-fed animals, HBO treatment also substantially reduces the accumulation of lipid oxidation products (conjugated dienes, trienes, and thiobarituric ac id-reactive substances) in plasma, in the low density lipoprotein and high density lipoprotein fractions of plasma, in the liver, and in the aortic ti ssues, In addition, HBO treatment prevents the decrease in plasma paraoxona se activity observed in rabbits fed cholesterol-rich diets. Similarly, in r egression studies, HBO treatment has no effect on the rate of plasma (or li poprotein) cholesterol decline but significantly accelerates aortic lesion regression compared with no treatment. Direct measures of aortic cholestero l content support these morphological observations. On the basis of these r esults, we conclude that repeated, but relatively short, exposure to HBO in duces an antioxidant defense mechanism(s) that is responsible for retarding the development or accelerating the regression of atherosclerotic lesions.