Phylloquinone vitamin prothrombin synthesis

Vitamin K activity is associated with several quinones, including phylloquinone (vitamin Kj), menadione (vitamin K3), and a variety of menaquinones (vitamin K2). These quinones promote the synthesis of proteins that are involved in the coagulation of blood. These proteins include prothrombin, factor VII (proconvertin), factor IX (plasma thromboplastin), and factor X (Stuart factor). A detailed discussion of blood coagulation is found in Chapter 22. The vitamin K quinones are obtained from three major sources. Vitamin K is present in vari-... 

Vitamin K (phylloquinone) regulates the synthesis of prothrombin and other proteins needed for blood to clot. 

The determination of vitamin K requirements is complicated by the intestinal bacterial synthesis of menaquinones and the extent to which these are absorbed and utilized (Section 5.1). Prolonged use of antibiotics leads to impaired blood clotting, but simple dietary restriction of vitamin K results in prolonged prothrombin time and increased circulating preprothrombin so it is apparent that bacterial synthesis is inadequate to meet requirements in the absence of a dietary intake of phylloquinone. Preprothrombin is elevated at intakes between 40 to 60 /xg per day, but not at intakes above 80 /rg per day (Suttie etal., 1988). 

Hemorrhagic disease of the newborn can develop readily because of (1) poor placental transfer of vitamin K, (2) hepatic immaturity leading to inadequate synthesis of coagulation proteins, and (3) the low vitamin K content of early breast milk. Prothrombin levels during this period are only about 25% of the adult levels. Severe diarrhea and antibiotics used to suppress diarrhea readily exacerbate the situation, so prothrombin levels can drop below 5% of the adult level and bleeding can occur. This condition is routinely prevented by the prophylactic administration of 0.5 to 1.0 mg of phylloquinone intramuscularly, or 2.0 mg given orally immediately after birth. 

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