Change in the distribution of alpha-tocopherol stereoisomers in rats after intravenous administration.

Synthetic alpha-tocopherol (alpha-Toc) contains equal amounts of eight different stereoisomers arising from three chiral centers in the phytyl tail. Of these, the four stereoisomers with the 2R configuration are generally more active than their corresponding 2S-isomers. We investigated the change in distribution of alpha-Toc stereoisomers in the plasma and tissues after intravenously administering all-rac- and SRR-alpha-Toc acetate. The concentration of 2R-isomers in the rat plasma after administering all-roc-alpha-Toc acetate was higher than that of the 2S-isomers. On the other hand, the concentration of 2R-isomers in the liver was lower than that of 2S-isomers up to 6 h. In the rat plasma after administering only SRR-alpha-Toc acetate, no SRR-alpha-Toc was detected after 6 h, although SRR-alpha-Toc in the liver was retained at a higher level than in the other tissues. We presume that the intravenously administered 2R- and 2S-isomers were easily transported into the liver from the plasma, the 2R-isomers being preferentially released from the liver into the blood, whereas the 2S-isomers remained in the liver for up to 6 h.