Influence of sources of dietary vitamin E on the maternal transfer of a-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 1mg allrac-a-tocopheryl acetate (synthetic form) is 1·00 IU and that of 1mg (RRR)-a-ocopheryl 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)-a-tocopheryl acetate:all-rac-a-tocopheryl acetate. Sixty female in-bred guinea pigs received either 40 or 80 mg vitamin E/kg diet with equal levels of (RRR)-a-tocopheryl acetate and all-raca-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 a-tocopherol analysis. Vitamin E analysis of fetal and neonatal tissues indicated a substantial transfer of 2H-labelled a-tocopherol across the placenta and through the mammary gland. Total a-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#0·05) was observed with natural compared with synthetic a-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 a-tocopheryl acetate of 1·36:1·00.