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Response of Plasma Levels of Vitamin A to a Dose of Vitamin A as an Indicator of Hepatic Vitamin A Reserves in Rats^1,2,

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

Rats were fed diets deficient [-A] or sufficient [+A] (3 mg retinol equivalents/kg) in vitamin A, and without [-RA] or with [+RA] (12 mg/kg) retinoic acid supplemntation, for up to 33 days. Rats with plasma vitamin A levels ranging from 7 to 62 µg/dl were studied at intervals during progressive depletion of liver stores of vitamin A (expt. 2) and when liver stores were nearly exhausted (<10 µg/g) or replete (up to 100 µg/g) with vitamin A (expt. 1). A dose of retinyl acetate in corn oil (20 µg retinol equivalents) was administered by intubation directly into the stomach. The relative dose response (RDR), expressed as a percentage and defined as the absolute magnitude of the rise in plasma vitamin A levels 5 hours after the dose of retinyl acetate, divided by the plasma level of vitamin A attained after 5 hours, was determined for each rat and correlated over a wide range of vitamin A plasma and liver levels. An RDR above 50% invariably was associated with low plasma levels (10 to 30 µg/dl) and low liver stores (<10 µg/g) of vitamin A, whereas an RDR of less than 40% was associated with plasma levels above 30 µg/dl and liver stores ranging from 3 to 100 µg/g.

KEY WORDS: • plasma levels vitamin A • hepatic levels vitamin A • vitamin A

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 To whom reprint requests should be addressed. current address: Department of Nutrition and Food Science, Massachusetts Institute of Technology, Room 20A-222, Cambridge, Massachusetts 02139.

Manuscript received 4 January 1978.