Vitamin K requirement in Danish anticoagulant‐resistant Norway rats ( Rattus norvegicus )

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 K 3 and sampling locality. Development of deficiency was slower for resistant rats that were supplemented with vitamin K 3 prior to the feeding test, suggesting storage of the vitamin K in a vitamin body pool. Intraperitoneal administration of vitamin K 1 revealed that 80 µg vitamin K 1 kg −1 bodyweight was sufficient to restore normal blood clotting activity in deficient rats, while 60 µg vitamin K 1 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. Copyright © 2003 Society of Chemical Industry