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Vitamin A Turnover in Rats as Influenced by Vitamin A Status¹

Kevin C. Lewis, Michael H. Green and Barbara A. Underwood^2,*

Nutrition Program, The Pennsylvania State University, University Park, PA 16802 ^* Department of Nutrition and Food Science, Massachusetts Institute of Technology, Cambridge, MA 02139

Vitamin A turnover was studied in rats fed vitamin A-sufficient (+A) or vitamin A-deficient (-A) diets for 24–25 days. Hepatic vitamin A stores of the +A group (543 µg) were significantly larger than those of the -A group (11 µg) and similarly, the plasma vitamin A concentration of the +A group (56 µg/dl) was significantly higher than that of the -A group (26 µg/dl). Rats were injected intravenously with plasma containing tritium-labeled retinol (³H-ROH) obtained from vitamin A-deficient donor rats previously fed ³H-ROH. Plasma samples from injected recipients were collected over a 48-hour period. Kinetic analysis of plasma tracer concentration versus time curves indicated that the data fit a three-pool model. The plasma vitamin A turnover rate of the +A group was significantly more rapid than that of the -A group (5.19 versus 1.98 µg/hour). Plasma fractional turnover rates for the +A group (1.31 hour^-1) were not significantly different from those of the -A group (0.90 hour^-1). The data suggest that for both dietary groups, the metabolism of retinol associated with the prealbumin and retinol-binding protein complex involved extensive recycling among the liver, plasma, interstitial fluid and peripheral tissues.

KEY WORDS: • vitamin A deficiency • vitamin A turnover

¹ Supported in part by NIH Grant AM-16578.

² To whom reprint requests should be sent at M.I.T. address.

Manuscript received 9 October 1980.

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