Distribution and metabolism of two orally administered esters of tocopherol

A comparison of the distribution of total radioactivity in rat tissue lipids after the oral administration of d,1‐3,4‐3H2‐α‐tocopheryl nicotinate and d,1‐α‐tocopheryl‐1’,2’‐3H2‐acetate in equimolar concentrations has demonstrated that there is considerable variation in the concentration of vitamin E in organs at different times after dosing. A higher total radioactivity was found in the tissues of animals receiving α‐tocopheryl nicotinate than after α‐tocopheryl acetate 12 hr after feeding with an emulsion, but not at most other time intervals studied. These findings indicate that the tissue uptake of vitamin E after oral dosage with nicotinate ester is, perhaps, poorer than that occurring after feeding with tocopheryl acetate, or that α‐tocopheryl nicotinate has a faster turnover than the acetate ester. Although total radioactivity in the blood and liver of those animals dosed with α‐tocopheryl acetate varied slightly with time, there was a high peak of radioactivity at 12 hr after dosage with nicotinate ester. In both groups of rats, the adrenals, ovaries, adipose tissue and heart appeared to extract vitamin E from the blood for a period of up to 48 hr postabsorptively. Metabolic products of tocopherol detected by glass‐fiber paper chromatography were found in both instances. This analysis revealed that, when orally administered, both α‐tocopheryl nicotinate and α‐tocopheryl acetate are extensively metabolized by the tissues of the rat. The metabolite most abundantly occurring under these conditions was α‐tocopheryl quinone. In the adrenal glands, however, the most highly labeled compound was unesterified tocopherol, which increased with time and comprised up to 90% of the chromatographed radioactivity. From the data obtained, it can be assumed that the adrenal tissue plays a definite role in the metabolism of vitamin E.