Absorption and Excretion of an Oral Dose of Tritiated Vitamin K₁ in Man

Abstract

S ummary . The radioactivity in the plasma, urine and faeces has been determined in three studies carried out in two normal men after an oral dose of tritiated vitamin K 1 (50–100 μCi). Radioactivity in the plasma was detected by 30 min, reached a peak at 2–4 hr and then declined relatively rapidly. A low level of radioactivity persisted in the plasma for at least 96 hr. Most of the radioactivity in the plasma at the peak time was in the form of vitamin K 1 as shown by thin‐layer chromatography; the remaining plasma radioactivity was due to water‐soluble material. Examination of serum taken at the time of peak absorption showed that most of the radioactivity could be floated to the top in the ultracentrifuge (in a medium of density 1.21) and appeared in the void volume on gel filtration (Sephadex G‐200): The results suggest that absorbed vitamin K 1 in plasma becomes associated with chylomicra mainly but that some may also be associated with other lipoproteins. Faecal excretion of radioactivity was maximal in the first 2 days and appeared to be essentially complete after 5 days; the total faecal radioactivity accounted for about 52% of the ingested dose of labelled vitamin K 1 , and about 18% of the dose was recovered as unchanged vitamin K 1 . The faecal results suggest that at least half of the ingested dose was absorbed. Excretion of radioactivity in the urine was greatest in the first 24 hr and 8–19% of the administered dose of labelled vitamin K 1 was recovered from the urine after 3 days. The urinary radioactivity was present in water‐soluble and chloroform‐soluble forms.