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Comparative Metabolism and Requirement of Vitamin K in Chicks and Rats¹

Departments of Biochemistry and Nutritional Sciences, College of Agricultural and Life Sciences, University of Wisconsin-Madison, Madison, WI 53706 ^* Second Department of Surgery, Kyoto University, 54-Kawahara-cho, Shogoin, Sakyo-ku, Kyoto 606, Japan

The metabolic basis for the high vitamin K requirement of chicks compared with rats was investigated. When chicks and rats were fed the same diet, containing 500 µg phylioquinone/kg, the total amounts of phylioquinone and its epoxide metabolite found in the liver and plasma were similar in both species. However, phyiloquinone 2,3-epoxide was present in high concentrations in chick liver and serum but not in rat liver and serum. This metabolite of the vitamin is normally reduced by a hepatic vitamin K epoxide reductase. The activity of this enzyme in chicks was 10% of that in rats, and the inability of chicks to effectively recycle the epoxide of vitamin K seems to be the major factor in its high requirement. Other species differences in vitamin K metabolism were observed. Much higher concentrations of bacterial menaquinones were present in rat feces compared with chick feces, but neither species had appreciable hepatic concentrations of menaquinones. Chicks, but not rats, were found to have a liver concentration of menaquinone-4 that exceeded that of phylloquinone. This vitamer was present even when its recognized precursor, menadione, was not present in the diet, and the data indicate that chicks convert phyiloquinone to menaquinone-4 under the conditions of these experiments. The mechanism of this conversion was not established.

KEY WORDS: • vitamin K • phylloquinone • rats • menaquinone-4 • chicks

¹ Supported by the College of Agricultural and Life Sciences of the University of Wisconsin-Madison, and in part by grants DK-14881 and HL-29586 from the National Institutes of Health, Bethesda, MD, and CRCR-1-1415 from the U.S. Department of Agriculture, Washington, DC.

Manuscript received 27 April 1992. Revision accepted 28 July 1992.

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