Influence of sources of dietary vitamin E on the maternal transfer of alpha-tocopherol to fetal and neonatal guinea pigs as determined by a stable isotopic technique.

The accepted biological potencies of vitamin E (United States Phamacopeia, 1985) for 1 mg all-rac-alpha-tocopheryl acetate (synthetic form) is 1.00 IU and that of 1 mg (RRR)-alpha-tocopheryl acetate (natural form) is 1.36 IU. In the present study, a stable isotopic (2H) technique was employed to evaluate the bioavailability of natural v. synthetic forms of vitamin E and to determine whether the potency of the forms is the stated relationship of 1.36:1.00 (RRR)-alpha-tocopheryl acetate:all-rac-alpha-tocopheryl acetate. Sixty female in-bred guinea pigs received either 40 or 80 mg vitamin E/kg diet with equal levels of (RRR)-alpha-tocopheryl acetate and all-rac-alpha-tocopheryl acetate throughout gestation and lactation. At late-term pregnancy (day 50 or 60) and during early lactation, dams and their corresponding fetuses or neonates were killed and various tissues collected for subsequent alpha-tocopherol analysis. Vitamin E analysis of fetal and neonatal tissues indicated a substantial transfer of 2H-labelled alpha-tocopherol across the placenta and through the mammary gland. Total alpha-tocopherol concentrations were significantly influenced by tissue type and dose level, but not by stage of gestation or lactation. The relative bioavailability (d3:d6) across fetal and neonatal tissues was on average 1.81:1.00, with a range from 1.62:1.00 to 2.01:1.00. Maternal tissues had a mean ratio of 1.77:1.00. A higher relative bioavailability (P<or=0.05) was observed with natural compared with synthetic alpha-tocopherol as shown by a higher d3:d6 ratio in all tissues examined. Vitamin E was highest in colostrum on day 2 then declined through to day 5. Results from this present experiment further question the accepted biological potencies of natural:synthetic alpha-tocopheryl acetate of 1.36:1.00.