Changes of K vitamins in portal and femoral venous plasma of rats after oral administration of phylloquinone and menaquinone-4.

To clarify the mechanism of absorption and metabolism of K vitamins (VK), we administered phylloquinone (K1) and menaquinone-4 (MK-4) orally to male Wistar rats whose portal and femoral veins were cannulated. Blood was collected 9 times up to 120 min later, and 50 microliters plasma was used for VK analysis by high performance liquid chromatography (HPLC) using a modification of our previous method. There were no significant differences between portal and femoral venous VK concentrations throughout all the experiments. When K1 and MK-4 were administered simultaneously, K1 appeared in plasma at 15 min, and MK-4 at 10 min. The concentration of MK-4 was significantly higher than that of K1 up to 60 min. In contrast to the single administration, the MK-4 concentration was reduced after 60 min. After K1 single administration, the MK-4 was not detected in either portal or femoral venous plasma up to 120 min. These results suggested that (1) the main absorption route of both VK may be the extra-portal pathway, (2) MK-4 is absorbed faster than K1 (3) some interactions may exist between K1 and MK-4 and (4) the intestinal cells might not be the major site to transform K1 into MK-4.