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Colonic Absorption of Menaquinone-4 and Menaquinone-9 in Rats

Shionogi Research Laboratories, Fukushima-ku, Osaka 553 ^* School of Pharmaceutical Sciences, Kitasato University, Minato-ku, Tokyo 108, Japan

The colonic absorption of menaquinones was examined in rats by the in situ loop method. The overall disappearance of [¹⁴C]menaquinone-4 from the colonal loop was 6% at 3 h and much slower than that of menadione. After administration of [¹⁴C]menaquinone-4 into the jejunal loop with bile, 17% of unchanged menaquinone-4 was recovered in the lymph after 6 h, but none was found when the administration had been into the colonal loop. Portal absorption of menaquinone-4 from the colon was detected and the unchanged form (23% of the absorbed radioactivity) was identified in the mesenteric venous blood. When menaquinone-9 was administered into the colon, almost all was recovered from the colonal loop. No transfer of menaquinone-9 from the colon into the lymph or blood was observed at 6 h after dosing. The present observations indicate that only a part of bacterially produced menaquinones is absorbed from the colon via the portal pathway, but the absorption rates of menaquinones decrease markedly with an increase in the number of isoprenoid units.

KEY WORDS: • menaquinones • colonic absorption • portal absorption • rats

Manuscript received 13 May 1991. Revision accepted 24 September 1991.

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