Alpha- and Gamma-Tocopherol in the Rat: in vitro and in vivo Tissue Uptake and Metabolism

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Abstract
In order to compare tissue uptake and metabolism of α- and γ-tocopherol in the rat, vitamin E-deficient male rats were injected intraperitoneally with a 1:1 mixture of dl-[3H]-α-tocopherol and dl-[14C]-γ-tocopherol. Blood and tissues were removed from the rats at 10, 19 and 27 hours after injection. In vitro incubations of plasma from these rats with red cells from deficient rats were performed, and α- and γ-tocopherol exchange led to an equilibrium after 6 hours. At equilibrium the red cells showed a slightly greater affinity for γ-tocopherol than α-tocopherol. Similar results were obtained when deficient red cells were incubated with an aqueous dispersion of α- and γ-tocopherol. Tissues from the injected rats were analyzed both for total radioactivity and for tocopherols, and showed approximately equal uptake of the two tocopherols at 10 hours, but a more rapid loss of γ-tocopherol than α-tocopherol after this time. Plasma and red cells analyses confirmed the in vitro incubation results with γ-tocopherol being taken up to a greater extent than α-tocopherol. It was concluded that rat tissues take up α- and γ-tocopherol to approximately the same extent, and in red cells a slight preference for γ-tocopherol exists. Tissues, however, showed a more rapid disappearance of γ-tocopherol.