A comparison of warfarin resistance and liver microsomal vitamin K epoxide reductase activity in rats.

Vitamin K-1 epoxide reductase activity was investigated in liver microsomal preparations from warfarin-resistant and -susceptible rats. One rat strain (TAS) is susceptible to the anticoagulant and lethal effects of warfarin and the other two strains are homozygous for warfarin resistance genes from either wild Welsh (HW) or Scottish (HS) rats. The enzyme in microsomal preparations from HW rat livers apparently has a reduced affinity for both warfarin and vitamin K-1 2,3-epoxide. The kinetic parameters for the enzyme activity in HS microsomal preparations indicated, however, that vitamin K-1 epoxide reductase in this warfarin-resistant strain was very similar, in respect of substrate and inhibitor affinities, to that prepared from susceptible (TAS) animals. Analysis of vitamin K-1 epoxide reductase activity in the livers of animals that had been orally treated with sodium warfarin (20 mg/kg body wt.) indicated that enzyme activity was inhibited in all three strains, although this dose is lethal only to animals of the TAS strain.