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Reduced Intestinal Absorption of Vitamin E by Low Dietary Levels of Retinoic Acid in Rats¹

Laboratory of Nutrition and Endocrinology, National Institute of Arthritis, Metabolism, and Digestive Diseases, Bethesda, MD 20205

It was observed that rats fed a low dietary level of retinoic acid had markedly lower plasma concentrations of -tocopherol than did rats fed the same amount of retinol. In this report, the possible mechanism by which retinoic acid alters vitamin E metabolism has been investigated. Weanling male rats were fed a complete purified diet with either retinol or retinoic acid at 4 mg/kg diet; plasma and tissues were analyzed after 2–5 weeks. The plasma -tocopherol concentration in rats ingesting retinoic acid was one-half that of rats ingesting retinol, and this difference also occurred in the liver and adipose tissue. Similar effects occurred in chicks. This low dietary level of retinoic acid had no effect on plasma triglyceride concentration, as has been reported for higher intakes, and plasma cholesterol and total lipids were also unaffected. Retinoic acid did not affect the rate of decrease in endogenous -tocopherol in normal rats fed a vitamin E-free diet for 3 weeks. In rats with mesenteric lymph cannulas, dietary retinoic acid caused a reduced absorption of ³H-labeled -tocopherol. In chicks fed retinoic acid, plasma and liver radioactivity 2.5 hours after an oral dose of ³H--tocopherol was one-fifth that of chicks fed retinol. More oxidation of -tocopherol occurred during absorption in rats fed retinoic acid than in those fed retinol, as evidenced by more -tocopherylquinone in the collected lymph. We postulate that dietary retinoic acid reduces the intestinal absorption of -tocopherol and may also promote its oxidation.

KEY WORDS: • retinoic acid • vitamin E metabolism

¹ Preliminary reports of this work were presented at the New York Academy of Sciences, Conference on Modulation of Cellular Interactions by Vitamin A and Derivatives (Retinoids), 10–12 March, 1980, and at the annual meeting of the American Institute of Nutrition, Anaheim, Calif., 13–18 April, 1980.

Manuscript received 26 August 1980.

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