Resistance to
warfarin has been connected to an increase in dietary requirement for
vitamin K in British strains of the Norway rat, Rattus norvegicus (Berk). This study examines
vitamin K requirement of Danish
anticoagulant-resistant Norway rats using a
vitamin K deficient feeding test. Wild
bromadiolone-resistant rats sampled from different localities in Denmark and rats from
bromadiolone-resistant and susceptible laboratory strains were fed on a
vitamin K deficient diet over a maximum period of 15 days. Development of
vitamin K deficiency, measured as reduced blood-clotting capacity, took place in 43% of the Danish resistant rats and was independent of sex, treatment with supplementary
vitamin K3 and sampling locality. Development of deficiency was slower for resistant rats that were supplemented with
vitamin K3 prior to the feeding test, suggesting storage of the
vitamin K in a
vitamin body pool. Intraperitoneal administration of
vitamin K1 revealed that 80 microg
vitamin K1 kg(-1) bodyweight was sufficient to restore normal blood clotting activity in deficient rats, while 60 microg
vitamin K1 kg(-1) bodyweight was insufficient. We conclude that
vitamin K requirement is moderately increased in Danish homozygous resistant rats whereas heterozygous resistant rats only have a minor increase in
vitamin K requirement compared with susceptible rats. We found no indication of different resistance types being present in our test material since
vitamin K requirement was not different between rats from separate sampling localities.