title: Temporal variation in the effects of warfarin on the vitamin K cycle.
abstract: In this in vivo study, the time-dependent effect of oral sodium warfarin was studied in male rats synchronized under a 12-hr light-dark cycle (light 0600-1800). Groups of 5 animals received an oral dose of 500 micrograms/kg of warfarin or saline at 0600 or 1800 and 1 mg/kg of vitamin K 8 hr later and the rats were sacrificed 240 min after vitamin K administration. The activities of the vitamin K reductase and vitamin K epoxide reductase were measured indirectly by determining the content of vitamin K1 and vitamin K epoxide reductase in the plasma and liver. The data obtained in control rats indicated that vitamin K and vitamin K 2,3 epoxide concentrations in plasma and liver were higher (P less than 0.05) at 1800 than at 0600. Warfarin had a greater (P less than 0.05) inhibitory effect on the vitamin K and vitamin K-epoxide reductases at 0600 compared to 1800; plasma levels of S- and R-warfarin did not vary with time of administration. The findings suggest that the activity of both reductases under control conditions, and the warfarin-induced inhibition of these enzymes varied depending on the time of drug administration.
authors.affiliation: Ecole de pharmacie, Université Laval, Québec, Canada.
authors.forename: G
authors.initials: G
authors.lastname: Soulban
authors.forename: G
authors.initials: G
authors.lastname: Labrecque
authors.forename: P M
authors.initials: PM
authors.lastname: Bélanger
mesh_terms: D000284:Administration, Oral; D000818:Animals; D002940:Circadian Rhythm / Q000502:physiology*; D004334:Drug Administration Schedule; D008099:Liver / Q000187:drug effects / Q000378:metabolism; D008297:Male; D006899:Mixed Function Oxygenases / Q000378:metabolism; D011808:Quinone Reductases / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D014812:Vitamin K / Q000378:metabolism*; D010837:Vitamin K 1 / Q000031:analogs & derivatives / Q000378:metabolism; D064417:Vitamin K Epoxide Reductases; D014859:Warfarin / Q000008:administration & dosage*
chemical_list: D014812:Vitamin K; C016186:vitamin K1 oxide; D014859:Warfarin; D010837:Vitamin K 1; D006899:Mixed Function Oxygenases; D064417:Vitamin K Epoxide Reductases; D011808:Quinone Reductases