Bioavailability of α-Tocopherol Fed with Retinol and Relative Bioavailability of D-α-Tocopherol or DL-α-Tocopherol Acetate

Abstract Two experiments were conducted to examine the effects of the form of α -tocopherol or interactions of α -tocopherol with vitamin A on its bioavailability. In Experiment 1, Holstein steers were fed a diet that was low in vitamins A and E for 1 mo; then, steers were blocked by body weight ( X ¯ = 97.5kg) and assigned randomly to one of four oral treatments: 1) no added vitamins, 2) 442mg of retinyl acetate, 3) 1342mg of D- α -tocopherol, or 4) 442mg of retinyl acetate and 1342mg of D- α -tocopherol. Each treatment was given as a pulse dose. Blood was sampled over a 36-h period. Concentrations of plasma retinyl palmitate peaked at 2 to 6h postsupplementation for all calves and then peaked again at 22 to 28h for calves receiving vitamin supplements. Concentrations of plasma α -tocopherol peaked earliest with D- α -tocopherol supplementation alone at 12 to 20h after supplementation, but simultaneous supplementation with retinyl acetate resulted in lower plasma α -tocopherol concentrations. Plasma retinyl palmitate decreased during peak α -tocopherol concentrations. In Experiment 2, blood and tissue were analyzed after a single gastric tube administration of a powder (DL- α -tocopheryl acetate) or a liquid (D- α -tocopherol) form of vitamin E to Holstein calves. Plasma and kidney concentrations of α -tocopherol were higher when calves were fed D- α -tocopherol than when calves were fed the DL- α -tocopherol acetate form. Concentrations in the liver, spleen, adipose tissue, heart, muscle, cellular blood fraction, and gut did not differ between the two forms.