Tissue distribution of K-vitamers under different nutritional regimens in the rat

Two forms of vitamin K [phylloquinone (K-1) and menaquinone-4 (MK-4)] were added to vitamin K-deficient rat food in varying amounts, These diets were given as the sole source of nutrition to rats for one week. The minimal dietary requirements (MDR) to attain maximal prothrombin synthesis were determined to be 0.6 and 6-10 mu g/g of food for K-1 and MK-4, respectively. The difference between both vitamers could be explained by the limited hepatic accumulation of MK-4. Next, vitamin K was offered to rats at concentrations ranging between 0.6 and 3000 mu g/g of food, and the tissue distribution of vitamin K was investigated after one week of administration. Accumulation of K-1 and MK-4 was found in all tissues investigated, but both the absolute tissue concentration and the ratio between K-1 and MK-4 were tissue-dependent. Highest values were found in liver and in heart, but since the heart contains no gamma-glutamylcarboxylase, the function of vitamin K in this tissue remains obscure. High tissue concentrations of MK-4 were also found in pancreas and testis after a diet containing K-1 exclusively. The data indicate that this conversion is tissue-specific, but neither the reason nor its mechanism are known. (C) 1998 Elsevier Science B.V.