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Maternal-Fetal Transfer of Ascorbic Acid in the Guinea Pig^1,2,3,

Institute of Human Nutrition and Department of Pediatrics, College of Physicians and Surgeons, Columbia University, New York, New York 10032

Placental transfer of ascorbic acid was studied in the guinea pig using an in situ placental perfusion technique. A total of 14 animals were studied during their last week of gestation. The fetus was shown to have higher plasma total ascorbic acid (TAA) levels than the mother prior to maternal ascorbic acid infusion. However, following maternal venous infusion this normal gradient for TAA (fetal > maternal) disappeared and a new gradient was established (maternal > fetal). As maternal plasma TAA levels rose, the level of TAA in the placental perfusate steadily increased to a maximal concentration of approximately 0.85 mg/dl. This occurred when maternal plasma TAA levels were above 3.0 mg/dl. These results demonstrate that a saturable or carrier-mediated transport mechanism is involved in the placental transfer of ascorbic acid in this species. The apparent Vmax (the maximal transport rate by the saturable system per gram placenta) and the K_t (or one-half saturation concentration) were estimated to be 8.3 nmoles/minute and 0.12 mM, respectively. Additional results are presented to suggest that dehydroascorbic acid (DHA) may be the predominant form of the vitamin crossing the guinea pig placenta.

KEY WORDS: • ascorbic acid • dehydroascorbic acid • placental transfer • pregnancy • maternal-fetal exchange • maternal-fetal transfer

¹ This work was supported by USPHS, NIH Grant, No. 5K04 HD00116 and 1R01 HD10167.

² A preliminary report was presented at the 62nd Annual Meeting of the Fed. Am. Soc. Exp. Biol.; Norkus, E., Bassi, J. & Rosso, P. (1978) Fed. Proc. 37, 332, A647.

³ The work reported in this paper was submitted by E. P. Norkus as part of his Ph.D. dissertation, Columbia University, 1978.

⁴ Present address: Dept. of Biochemistry and Drug Metabolism, Roche Research Center, Hoffmann La Roche, Inc., Nutley, New Jersey 07110.

Manuscript received 12 April 1979.