Dietary alpha-tocopherol decreases alpha-tocotrienol but not gamma-tocotrienol concentration in rats

We previously showed that alpha- and gamma-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 alpha-tocopherol and alpha- and gamma-tocotrienols. To clarify the nature of tocotrienol metabolism, we studied the distribution of alpha- or gamma-tocotrienol in rats fed alpha- or gamma-tocotrienol without alpha-tocopherol, and the effect of alpha-tocopherol on their distribution. Wistar rats (4-wk-old) were fed a diet with 50 mg alpha-tocotrienol/kg alone or with 50 mg alpha-tocopherol/kg in expt. 1, and a diet with 50 mg gamma-tocotrienol/kg alone or with 50 mg alpha-tocopherol/kg in expt. 2, for 8 wk. alpha-Tocotrienol was detected in various tissues and plasma of the rats fed alpha-tocotrienol alone, and the alpha-tocotrienol concentrations in those tissues and plasma decreased (P < 0.05) by the dietary alpha-tocopherol in the rats fed alpha-tocotrienol with alpha-tocopherol. However, gamma-tocotrienol preferentially accumulated in the adipose tissue and skin of the rats fed gamma-tocotrienol alone, and the dietary alpha-tocopherol failed either to decrease (P >/= 0.05) gamma-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 gamma-tocotrienol, in the rats fed gamma-tocotrienol with alpha-tocopherol. These data suggest that alpha-tocopherol enhances the alpha-tocotrienol metabolism but not the gamma-tocotrienol metabolism in rats.