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Mechanisms of Absorption, Transport and Tissue Uptake of RRR--Tocopherol and d--Tocopherol in the White Rat^{1, 2,}

Bureau of Nutritional Sciences, Food Directorate, Health Protection Branch, Health and Welfare Canada, Tunney's Pasture, Ottawa, Ontario, Canada K1A 0L2

The metabolism of - and -tocopherol was studied in three groups of rats that were fed a modified AIN-76 diet containing normal (NE, 0.2 g -tocopherol/kg), high (HE, 1.0 g -tocopherol/kg) or low (LE, <0.02 -tocopherol/kg) vitamin E for 3 mo. After 1, 2 and 3 d of an oral dose of 20 mg of -tocopherol, -tocopherol or both, the levels of the two vitamers were measured in plasma and tissues and in some cases in isolated microsomal and mitochondrial fractions from liver. Twenty-four hours after an oral dose of 20 mg -tocopherol the levels of -tocopherol in plasma and tissues remained constant and higher levels of -tocopherol were found in tissues in which low -tocopherol levels could be found such as in the LE group. In spite of this, it was enabled to remain there, after 2 and 3 d -tocopherol had decreased levels in all tissues. When given in combination with -tocopherol, the levels of -tocopherol were lower than when -tocopherol was given alone. Microsomes and mitochondria from livers of LE group bound five and nine times more -tocopherol than -tocopherol in rats dosed with equal amount of - or -tocopherol, respectively. These data indicate that the mechanisms that regulate the metabolism of vitamin E are highly specific for -tocopherol. Moreover, the relative amount of -tocopherol determined the levels of -tocopherol in tissues. However, the retention of -tocopherol in tissues did not depend on the presence of -tocopherol. This observation may be due to preferential binding of -tocopherol by soluble proteins and cellular membranes such as those of microsomes and mitochrondria and could well explain why -tocopherol is the vitamer with more vitamin E potency.

KEY WORDS: • vitamin E • -tocopherol • -tocopherol • nutrient interaction

¹ Bureau of Nutritional Sciences Publication No. 230.

² A preliminary report of these data was presented at the 1983 Federation of the American Societies for Experimental Biology Meeting in Chicago, IL [BEHRENS, W. A. & MADERE, R. (1983) Studies on the absorption, plasma transport and tissue uptake and retention of - and -tocopherol. Fed. Proc. 42: 813 (abs. 3051)].

³ To whom correspondence and reprint requests should be sent.

Manuscript received 20 May 1986. Revision accepted 15 May 1987.