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Biliary and Urinary Excretion and Enterohepatic Recycling of Vitamin A in Sheep¹

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

Mature ewes fitted with bile duct cannulae and urinary bladder catheters were used to study the excretion and enterohepatic recycling of vitamin A. In the first experiment, in which collected bile was replaced by duodenal infusion of unlabeled bile, 55.9% of the activity injected as retinoic acid-14-¹⁴C was recovered in the bile in 24 hours and 39.6% in the urine. When retinyl acetate-11,12-³H was injected, only 7.9% of the activity appeared in the bile in 24 hours and 8.7% in the urine. This supports the proposed roles of retinyl esters as storage forms, and retinoic acid as a possible end product, of vitamin A metabolism. In a second experiment, 22.9% of the activity from retinyl acetate-11,12-³H was recovered in the bile in 24 hours when collected bile was not replaced, but this increased to 31.0% (P < 0.001) when bile was replaced. Differences in vitamin A status may explain the different biliary recoveries of the radioactivity from retinyl acetate-11,12-³H (7.9% vs. 31.0%) obtained on separate occasions under similar conditions. In the final experiment 25.3% of the activity infused into the duodenum as ¹⁴C-labeled biliary vitamin A metabolites was excreted in the bile in 24 hours, indicating substantial recycling of vitamin A metabolites from the intestine to the liver of sheep.

² Supported in part by Public Health Service Research Grant no. Am 13326 from the National Institute of Arthritis and Metabolic Diseases.

³ Preliminary reports of these results were presented at the annual meeting of the American Society of Animal Science, University Park, Pa., August 3, 1970 (J. Anim. Sci. 31: 244 (abstr.)) and at the Midwestern Section Meeting of the American Society of Animal Science, Chicago, Ill., November 27, 1970 (J. Anim. Sci. 31: 1039 (abstr.)).

⁴ Present address: Department of Animal Science, University of California, Davis, Calif. 95616.

Manuscript received 8 December 1970.