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Quantitation of the Enterohepatic Circulation of Retinol in the Rat^1,2,

U.S. Department of Agriculture Human Nutrition Research Center on Aging at Tufts University, Boston, MA 02111

Studies were done to determine whether vitamin A is reabsorbed in the enterohepatic circulation in forms that can be reutilized by the body for vision and reproduction. Micelles containing [11,12(n)-³H]retinol were administered orally to mesenteric lymph duct-cannulated rats. Lymph containing [³H]retinyl esters and small amounts of [³H]retinol and [³H]retinaldehyde was collected from these rats and an aliquot was injected into the jugular vein of a second group of mesenteric lymph duct-cannulated rats. The total radioactivity recovered in 24-h lymph collections from recipient rats was only 1.6% of that injected, and the [³H]retinyl esters, [³H]retinol and [³H]retinaldehyde recovered was only 0.9% of that injected. Thus, the amount of vitamin A recovered in the enterohepatic route in forms that can be reutilized by the body for vision and reproduction appears to be very small. Notable differences were observed in the composition of mesenteric lymph containing newly absorbed vitamin A and mesenteric lymph containing recycled vitamin A. In the former, 87% of the total lymph radioactivity was associated with retinyl esters, 5% with retinol, 3% with retinaldehyde and 5% with unidentified mostly nonpolar compounds. In the latter, only 41% of the total lymph radioactivity was associated with retinyl esters, 12% with retinol, 3% with retinaldehyde and 44% with unidentified mostly polar compounds.

KEY WORDS: • vitamin A • retinol • retinyl esters • retinaldehyde • enterohepatic circulation

¹ This study was supported in part by the Center for Gastroenterology Research on Absorptive and Secretory Processes of the New England Medical Center Hospitals, Boston, MA; by PHS Grant No. 1 P30 AM39428 awarded by the National Institute of Diabetes and Digestive Kidney Diseases; and by U.S. Department of Agriculture Contract No. 53-3K06-5-10.

² An abstract of this work was presented at the meeting of the Federation of American Societies for Experimental Biology, March 29–April 2, 1987, Washington, DC [Ribaya-Mercado, J. D., Kassarjian, Z. & Russell, R. M. (1987) The enterohepatic circulation of vitamin A in rats is minimal. Fed. Proc. 46: 1190 (abs.)].

³ To whom reprint requests should be addressed.

Manuscript received 12 June 1987. Revision accepted 16 September 1987.