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Effects of Dietary Vitamin A Deficiency, Retinoic Acid and Protein Quantity and Quality on Serially Obtained Plasma and Liver Levels of Vitamin A in Rats^1,2,

Nutrition Program, Division of Biological Health, the Pennsylvania State University, University Park, Pennsylvania 16802

Rats were fed vitamin A-deficient diets either alone, supplemented with retinoic acid (RA), or of limited protein quality or quantity (7% rice or 7% casein protein); one group was fed 7% rice protein supplemented with vitamin A. Plasma and liver levels of vitamin A were determined serially. Plasma levels in rats fed otherwise adequate vitamin A-deficient diets remained above 30 µg/dl until liver reserves were below 10 µg/g tissue, at which point plasma levels decreased in some but not all rats while liver levels continued to decline (at a slower rate) to levels as low as 3 µg/g. Supplementation with RA caused an immediate and sustained reduction of 15 to 20 µg/dl in circulating vitamin A. At 7% dietary protein, plasma levels of vitamin A remained above 30 µg/dl when casein protein was fed or when the rice protein diet was supplemented with dietary vitamin A, but not when the rice protein diet was fed without an exogenous source of the vitamin. A scheme is proposed suggesting possible regulatory mechanisms that might control homeostatic levels of plasma vitamin A.

KEY WORDS: • plasma vitamin A • liver vitamin A • retinoic acid • protein quality • protein quantity

¹ Supported in part by NIH Grant AM-16578.

² Presented in part at the Annual Meeting of the Federation of American Societies for Experimental Biology, Chicago, Illinois, 1977; Abstract: Keilson, B., Lewis, K. C., Underwood, B. A. & Loerch, J. D. (1977) Effects of liver stores, dietary intake, and tissue utilization of vitamin A in the regulation of plasma vitamin A levels in rats. Federation Proc. 36 (Abstr. 4567), 1135.

³ Current address: Department of Nutrition and Food Science, Massachusetts Institute of Technology, Room 20A-207, Cambridge, Massachusetts 02189.

Manuscript received 4 January 1978.

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