Clearance from Plasma and Excretion in Urine, Faeces and Bile of an Intravenous Dose of Tritiated Vitamin K1 in Man

Vitamin K₁-³H (1 mg; 12 μCi) was injected intravenously into three normal men, into three patients undergoing duodenal intubation and into a patient with T-tube drainage of the common bile duct. In the normal subjects lipid-soluble radioactivity (representing the injected vitamin K₁-³H) disappeared rapidly from the plasma: the clearance curve for the first 6 hr could be resolved graphically into two exponential functions, the first with a T ® of 20–24 min and the second with a T ® of 121–150 min: water-soluble radioactivity, presumed to be metabolic products, appeared in the plasma within 30 min after injection, reached a peak at 2 hr and remained near this level for 24 hr. Of the injected radioactivity in the normal subjects, 19–26% was recovered in the urine after 3 days and 34–38% in the faeces after 5 days: most of the radioactive material in the faeces was lipid-soluble, which on thin-layer chromatography had a polarity between that of vitamin K₁ and vitamin K₁γ-lactone. In the patients undergoing duodenal intubation, radioactivity was detected in the duodenal juice within 20–40 min after injection of vitamin K₁-³H. Radioactivity was also detected in the bile in the patient with T-tube drainage of the common bile duct. Most of the radioactivity in the duodenal juice and bile was water-soluble. It seems likely that the radioactivity appearing in the faeces after intravenous injection of vitamin K₁-³H is derived from biliary excretion of water-soluble conjugated metabolites which become lipid-soluble by decon-jugation during their passage through the bowel.