INDUCTION OF PROTHROMBIN SYNTHESIS BY K-VITAMINS COMPARED IN VITAMIN-K-DEFICIENT AND IN BRODIFACOUM-TREATED RATS

Vitamin K is a group name for a number of prenylated 2-methyl-1,4-naph toquinones, which may differ in their ability to function as a cofacto r for prothrombin biosynthesis. To quantify the bioactivity of differe nt forms of vitamin K, two experimental animal systems are frequently used: vitamin K-deficient rats and anticoagulated rats, In this paper both models are compared, and it is shown that the results obtained de pend on the model used. The main reason for this discrepancy is the di fference in recycling of vitamin K-epoxide, which results in a 500 tim es higher vitamin EI requirement in anticoagulated rats. Absorption an d hepatic accumulation of long chain menaquinones seem to be restricte d to a maximum, whereas also the lipophilic nature of long chain menaq uinones may hamper the quinone-quinol reduction in anticoagulated anim als. If these data may be extrapolated to patients, food items rich in K-1 and MK-4 would be expected to influence the stability of oral ant icoagulation to a much larger extent than food items primarily contain ing higher menaquinones. (C) 1998 Elsevier Science B.V.