Dietary α-Tocopherol Decreases α-Tocotrienol but Not γ-Tocotrienol Concentration in Rats

We previously showed that α- and γ-tocotrienols accumulate in adipose tissue and skin but not in plasma or other tissues of rats fed a tocotrienol-rich fraction extracted from palm oil containing α-tocopherol and α- and γ-tocotrienols. To clarify the nature of tocotrienol metabolism, we studied the distribution of α- or γ-tocotrienol in rats fed α- or γ-tocotrienol without α-tocopherol, and the effect of α-tocopherol on their distribution. Wistar rats (4-wk-old) were fed a diet with 50 mg α-tocotrienol/kg alone or with 50 mg α-tocopherol/kg in expt. 1, and a diet with 50 mg γ-tocotrienol/kg alone or with 50 mg α-tocopherol/kg in expt. 2, for 8 wk. α-Tocotrienol was detected in various tissues and plasma of the rats fed α-tocotrienol alone, and the α-tocotrienol concentrations in those tissues and plasma decreased (P < 0.05) by the dietary α-tocopherol in the rats fed α-tocotrienol with α-tocopherol. However, γ-tocotrienol preferentially accumulated in the adipose tissue and skin of the rats fed γ-tocotrienol alone, and the dietary α-tocopherol failed either to decrease (P ≥ 0.05) γ-tocotrienol concentrations in the adipose tissue and skin or to increase (P ≥ 0.05) in the urinary excretion of 2,7,8-trimethyl-2(2′-carboxymethyl)-6-hydroxycroman, a metabolite of γ-tocotrienol, in the rats fed γ-tocotrienol with α-tocopherol. These data suggest that α-tocopherol enhances the α-tocotrienol metabolism but not the γ-tocotrienol metabolism in rats.