Biopotencies in rats of several forms of alpha-tocopherol.

The bipotencies of several forms of vitamin E were determined by the rat fetal-resorption bioassay. RRR-alpha-tocopheryl acetate compared with 2-ambo-alpha-tocopheryl acetate had a mean relative potency (RP) of 1.66, significantly higher than the currently accepted value of 1.36. RRR-alpha-tocopheryl hydrogen succinate compared with 2-ambo-alpha-tocopheryl acetate had a mean RP of 1.125, significantly lower than the currently accepted value of 1.21. RRR-alpha-tocopherol compared with 2-ambo-alpha-tocopherol had a mean RP of 1.31, not significantly different from the currently accepted value of 1.36. Some preparations of all-rac-alpha-tocopheryl acetate compared with 2-ambo-alpha-tocopheryl acetate had a mean RP of 0.81, and compared with RRR-alpha-tocopheryl acetate had a mean RP of 0.52. Both RP values are significantly lower than the currently accepted values of 1.00 and 0.725 (the reciprocal of 1.36) respectively. Similar biological activities were obtained for oily and dry preparations of the same forms of alpha-tocopheryl acetate. A basic assumption of stoichiometric equivalence for the acetate and hydrogen succinate of RRR-alpha-tocopherol, inherent in the currently accepted values, was shown to be incorrect. The results show that the unit/weight relationships for the various forms of vitamin E currently assigned by the National Formulary have not been validated using a bioassay based on biological function.