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Biliary Excretion of ¹⁴C-Labeled Vitamin B-6 in Rats¹

Departments of Medicine and Biochemistry, Indiana University School of Medicine and the Richard L. Roudebush Veterans Administration Medical Center, Indianapolis, IN 46223

The biliary excretion of vitamin B-6 was studied in the intact rat and isolated perfused rat liver. In the whole animal, 21% of the radioactivity administered intravenously as [¹⁴C]pyridoxine was excreted in the urine over 4 hours, whereas only 2.1% was recovered in the bile. In the perfused liver, 3% of the radioactivity added to the medium was detected in the bile after 4 hours of perfusion. These data suggest that biliary excretion and enterohepatic circulation of vitamin B-6 probably play only a minor role in the overall economy of this vitamin. The concentration of the radiolabeled B-6 compounds in the bile of perfused liver was much higher than that in the perfusate and the pattern of the distribution of radioactivity among different B-6 compounds was also different. These results suggest that [¹⁴C]pyridoxine and its metabolites are released separately by the hepatocytes into the bile and the perfusate and that paracellular transport of vitamin B-6 is not the predominant pathway for the biliary excretion of this vitamin.

KEY WORDS: • vitamin B-6 • pyridoxine • enterohepatic circulation • bile • urine • liver

¹ This work was supported by the Veterans Administration.

Manuscript received 29 October 1982.