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

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

Six ram lambs were injected intravenously with vitamin A acetate labeled with tritium. Liver was sampled by aspiration biopsy after 5, 33 and 61 days and then at 14-day intervals until 187 days after injection. Jugular blood was sampled frequently for the first 5 days and at the time of each liver biopsy. Feces and urine were collected for the first 5 days and for a 24-hour period immediately prior to each liver biopsy. Ether extracts of serum collected 5 minutes after dosing accounted for only 5.16% of the injected radioactivity. Liver vitamin A reserves decreased from 260 µg/g of liver at 5 days to 89 µg/g at 89 days. Radioactivity decreased a proportionate amount during this period. Depletion from the liver was then stopped by vitamin A supplementation. A half-time of 75 days was calculated from the decrease in the specific activity of liver vitamin A between 89 and 187 days. Detection of radioactivity in all blood samples supported the conclusion that there was continuous turnover of vitamin A stores. Ether extracts of fecal samples contained traces of radioactivity. Radioactivity was not detected in urine.

² This investigation was supported in part by Public Health Service Research Grant no. AM 08355-02 from the National Institute of Arthritis and Metabolic Diseases.

³ Present address: University of Missouri, Columbia, Missouri.

Manuscript received 13 June 1966.