Prolongation by warfarin of "template" bleeding time in rats: a vitamin K-dependent effect

Administration of warfarin to rats induced not only the well-known anticoagulant effect, but also an impairment of primary hemostasis as reflected by a significant prolongation of the "template" bleeding time. This effect was very closely associated with lowering of the prothrombin complex level and was reversed by administration of vitamin K. It is suggested that some of the clotting factors known to be vitamin K-dependent also play a role in primary hemostasis; alternatively, a putative vascular "bleeding factor" could be modulated by vitamin K availability.