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Mobilization of Liver Vitamin A in Mature Sheep^{1, 2,}

Department of Animal Sciences, University of Kentucky, Lexington, Kentucky 40506

Six mature rams averaging 63.3 kg were injected intrajugularly with 268 µCi of 11,12-³H-vitamin A acetate in 4 ml of aqueous 20% Tween 80. The sheep were fed alfalfa hay ad libitum plus 680 g of cracked shelled corn per head daily, supplemented with vitamin A palmitate at a level necessary to maintain liver vitamin A stores. The decline in serum radioactivity postinjection indicated rapid clearance of the injected dose of vitamin A from the blood. The excretory pattern of radioactivity in the feces and urine during 14 days postinjection suggested equilibration of body vitamin A stores. Liver was sampled at 14-day intervals postinjection by aspiration biopsy and analyzed for vitamin A and tritium activity. Vitamin A turnover in the liver was calculated using changes in specific activity units (dpm/µg vitamin A). The half-time of liver vitamin A was 163 ± 48 days and the turnover time was 234 ± 69 days. Using an average liver weight of 1 kg per ram, daily turnover rate of vitamin A was 968 ± 84 µg.

² Supported in part by Public Health Service Research Grant no. AM 08355 from the National Institute of Arthritis and Metabolic Diseases.

Manuscript received 12 May 1969.