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Effects of various tocopherol‐containing diets on tocopherol secretion into bile
Author(s) -
Yamashita Kanae,
Takeda Noriko,
Ikeda Saiko
Publication year - 2000
Publication title -
lipids
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.601
H-Index - 120
eISSN - 1558-9307
pISSN - 0024-4201
DOI - 10.1007/bf02664766
Subject(s) - tocopherol , clinical chemistry , chemistry , vitamin e , medicine , lipidology , endocrinology , biochemistry , biology , antioxidant
γ‐Tocopherol is abundant in common vegetable oil, but its concentration in plasma and liver is much lower than that of α‐tocopherol. Discrimination between different forms of tocopherol is thought to take place via the hepatic α‐tocopherol transfer protein (α‐TTP). γ‐Tocopherol, with a low binding capacity to α‐TTP, is thought to be excreted via the bile. Our previous studies showed that γ‐tocopherol administered with sesame seed exhibits significantly higher concentrations in the plasma and liver of rats than γ‐tocopherol alone. Thus, we attempted to confirm whether a much higher amount of γ‐tocopherol rather than γ‐tocopherol would be secreted in the bile, and whether sesame seed would suppress the secretion of γ‐tocopherol. In one experiment, we examined the concentrations of α‐or γ‐tocopherol in the plasma, liver, and bile of rats fed diets containing 300 mg/kg of α‐tocopherol, 300 mg/kg of γ‐tocopherol, or 300 mg/kg each of α‐tocopherol+γ‐tocopherol, and in the other experiment, we compared the γ‐tocopherol concentrations of rats fed a diet of γ‐tocopherol alone to those of rats fed a γ‐tocopherol+sesame seed diet (each diet contained 300 mg/kg γ‐tocopherol). The bile collection was done over 6 h. The γ‐tocopherol concentration in the bile was markedly lower than that of α‐tocopherol, paralleling the concentrations in the plasma and liver. Intake of α‐tocopherol and γ‐tocopherol together further lowered the concentration of γ‐tocopherol in the bile as well as in the plasma and liver, compared to the intake of γ‐tocopherol alone. The γ‐tocopherol concentration in the bile, as well as in the plasma and liver, was markedly higher in the sesame seed‐fed group than in the γ‐tocopherol alone group. We found that the concentrations of α‐ or γ‐tocopherol in the bile showed a good correlation with the concentrations of α‐ or γ‐tocopherol in the liver, though the concentrations in the bile were substantially lower than those in the liver. These findings suggest that secretion into the bile is not a major metabolic route of α‐ or γ‐tocopherol.