Vitamin K and coumarin anticoagulants: dependence of anticoagulant effect on inhibition of vitamin K transport. 
Coumarin anticoagulants inhibit the release of plasma clotting factor VII by vitamin K in liver slices from vitamin K-deficient animals without inhibition of protein synthesis.  When the ratio of vitamin K to coumarin anticoagulant is kept constant, but the concentrations are increased, the inhibition disappears.  This suggests that the pharmacological action of coumarin anticoagulants depends on irreversible inhibition of normal vitamin K transport to its site of action.  At higher concentrations of vitamin K the inhibition can be surmounted, because vitamin K can enter the cell by an alternate route that is not inhibited by coumarin anticoagulants.