Interrelationship and competition of α- and λ-tocopherol at the level of intestinal absorption, plasma transport and liver uptake

Abstract

α- and λ-Tocopherol (T) were measured in the plasma of 3 groups of rats that were fed a normal or modified AIN-76 diet containing normal (NE), high (HE) or low (LE) vitamin E for 3 months. α-T levels (μg/ml±SD; n=10) were 7.6±1.0 (NE), 19.3±5.1 (HE) and 0.48±0.43 (LE). λ-T levels were 0.32±0.16 (NE), 0.02±0.05 (HE) and 0.20±0.30 (LE). 24 hrs after an oral dose of 50 mg λ-T; α-T levels (n=3) were 7.0±1.2 (NE), 10.7±3.7 (HE) and 1.0±0.3 (LE). λ-T levels were 5.7±2.2 (NE), 0.83±0.46 (HE) and 10.8±3.8 (LE). When 3 rats from groups NE and HE were fed low vitamin E for 3 days prior to the administration of 50 mg λ-T; α-T levels were 4.8±1.3 (NE) and 7.1±1.5 (HE); λ-T levels were 5.9±2.0 (NE) and 4.6±2.6 (HE). When rats in group LE received 50 mg α-T, levels increased to 10.0±0.8 μg α-T/ml and were 8 times higher than those of λ-T when a dose of 50 mg of each of α- and λ-T were fed. None or traces of λ-T were found in a liver cytosol protein (32000 MW) that binds α-T specifically (α-TBP) in all three groups. Small amounts of λ-T were detected in α-TBP in LE rats after they were fed 50 mg of λ-T. These data suggest that the mechanisms for intestinal absorption, plasma transport and liver uptake of vitamin E are specific for α-T. Only when the concentration of α-T is low, can λ-T successfully compete for binding sites at these three levels.