Studies of the metabolism of alpha-tocopherol stereoisomers in rats using [5-methyl-C-14]SRR- and RRR-alpha-tocopherol

We investigated the distribution and metabolism of SRR-alpha-tocopherol (SR R-alpha-Toc), synthetic alpha-Toc compared with RRR-alpha-Toc, in rats afte r a single oral administration of 2 mg (20 mu Ci) SRR- and RRR-alpha-[5-met hyl-C-14]Toc. In the liver, there was no difference in the recovery of radi oactivity until 12 h after administration, and it reached a maximum of 4.4% of the dose after 12 h, but in other tissues, radioactivity derived from R RR-alpha-Toc was clearly higher than that derived from SRR-alpha-Toc after 12 h, For 96 h after administration, urinary excretions of SRR-alpha-Toc we re 7.8% of the dose and significantly greater than that of RRR-alpha-Toc, w hich was 1.3% of the dose. On the other hand, total fecal excretions of SRR - and RRR-alpha-Toc were 87.6% and 83.0%, respectively Therefore, radioacti vity in the urine was assumed to have transferred out of the liver. Further more, the urine samples were hydrolyzed with 3 N methanolic HCl and analyze d by high performance liquid chromatography (HPLC) and liquid chromatograph y/mass spectrometry. The results showed that about 73% of the total radioac tivity injected into HPLC was found to be 2,5,7,8-tetramethyl-2-(2'-carboxy ethyl)-6-hydroxy chroman (alpha-CEHC), as well as RRR-alpha-Toc. Thus, ther e is no difference between SRR-alpha-Toc and RRR-alpha-Toc in metabolic pat hways, and it is suggested that SRR-alpha-Toc discriminated in the liver is rapidly metabolized by the liver and excreted as the conjugate of alpha-CE HC in the urine.