Relative bioactivity of alpha- and gamma-tocopherol calculated from respiration parameters in rat liver mitochondria

In experiments with male wistar rats the influence of dl-alpha-tocopherol as well as dl-gamma-tocopherol on both the respiration of liver mitochondria and membrane lipid peroxidation has been investigated. For a test period of 8 weeks the animals were fed isoenergetic diets containing either no vitamin E or 46 mg d-alpha-tocopherol equivalents/kg diet as dl-alpha-tocopherol (60 ppm) or dl-gamma-tocopherol (480 ppm). The diets contained 6% of a synthetic triglyceride mixture rich in polyunsaturated fatty acids (about 60%). The measurements of the P/O ratios and corresponding respiratory control index (RCI) values for several substrates (alpha-ketoglutarate, malate/glutamate, succinate) indicated that under vitamin E-deficient conditions the mitochondria showed an increased respiratory intensity accompanied with an elevated lipid peroxidation. The oxidative phosphorylation itself was not affected. These deficiency symptoms could be normalized by the applied amounts of both tocopherols. In this respect dl-gamma-tocopherol showed a more distinct bioactivity than previously proposed. Based on the investigated parameters we calculated for dl-gamma-tocopherol an average bioactivity of 28% compared to that of dl-alpha-tocopherol.