Male weanling mice were placed on purified diets containing 20% safflower oil (highly unsaturated) or 20% coconut oil (full saturated) or on Purina Chow. Three months later, a 5% suspension of pooled blood was irradiated with 0-20 krads, and the percentage of hemolysis or potassium loss measured at various times thereafter. When the diets were supplemented with tocopherol (vitamin E), there were no significant differences in postirradiation hemolysis or potassium loss between cells from the two purified diets, despite considerable shifts in the relative amounts of unsaturated fatty acids in the cell membranes. When the two purified diets contained no tocopherol, however, the cells were not only more sensitive to hemolysis and potassium loss than cells from animals fed tocopherol, but the cells from the animals on the saturated fat diet were markedly more sensitive than those from animals on the unsaturated fat diet. This effect could be reversed by adding tocopherol (20 μg/g) to the diet 24 hr before obtaining the blood sample, or by preirradiation incubation of the cells in vitro with free tocopherol or with serum from animals fed a diet supplemented with tocopherol. Postirradiation incubation of the cells with free tocopherol had no effect on radiosensitivity. These results suggest that the presence of sufficient antioxidant, rather than the degree of saturation of dietary fats, may be the important factor in erythrocyte membrane radiosensitivity. Furthermore, it appears that a diet high in saturated fatty acids may not contain enough antioxidant to fulfill the erythrocyte membrane requirement.

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