Biliary excretion of radioactivity after intravenous administration of [3H]25-hydroxyvitamin D3 in man

The biliary excretion of radioactivity after intravenous [3H]25-hydroxyvitamin D3 was studied in nine patients with T-tube bile drainage. The mean +/- SD 24-hr radioactivity excretion in T-tube bile expressed as a percentage of the administered dose was 6.7 +/- 2.9%; after correction for incomplete bile collection, the value obtained was 16.0 +/- 11.1%. Chloroform solubility of biliary radioactivity increased from 27.4 +/- 8.9% to 72.9 +/- 10.1% following incubation with beta-glucuronidase. High-performance liquid chromatographic analysis of chloroform extracts of bile revealed that most of the eluted radioactivity was more polar than [3H]25-hydroxyvitamin D3. No free [3H]25-hydroxyvitamin D3 was demonstrated. Thus in man, most of the biliary radioactivity excreted following [3H]25-hydroxyvitamin D3 is in the form of water-soluble compounds, mainly glucuronides. However, our results suggest that glucuronides of metabolites other than 25-OHD3 are predominantly formed.