Studies on Riboflavin Metabolism in the Rat. V. Degradation of Riboflavin‐2‐¹⁴C

Abstract

Riboflavin-2-14C was administered orally or intraperitoneally to female Wistar rats in order to study the metabolic fate of the vitamin. Almost all the radioactivity was found in the urine, faeces, carcass and expired COe within 24 hours. The chemical recovery of riboflavin was lower, indicating partial degradation. Approximately 1 % of the radioactivity was recovered as 14COg. Following oral administration more than half of the radioactivity excreted in the urine was in the form of metabolites. Paper chromatography of urine revealed three unidentified labelled metabolites. After intraperitoneal administration only negligible amounts of non-riboflavin radioactivity were present in the urine. It is suggested from these data that the enzymes responsible for the degradation were saturated at the highest plasma concentrations reached. It is concluded that riboflavin, ingested orally within the dose range of 0.08 to 2.5 mg/rat, is eliminated to equal extents by degradation and by urinary excretion. This also seems to be the case at physiological conditions of vitamin intake.

Studies on Riboflavin Metabolism in the Rat. VI. Properties of Radioactive Metabolites Excreted after Administration of Riboflavin‐2‐14C

“…The animals received one dose (1-2 ml) of W-labelled riboflavin either orally as a solution or subcutaneously as a suspension. Solutions and suspensions of riboflavin were prepared as previously described (CHRISTENSEN 1971). The dose of riboflavin varied from 0.08 mg (orally) to 100 mg (subcutaneously).…”

“…Degradative metabolites of riboflavin have recently been demonstrated in the rat (CHRISTENSEN 1971). In this study investigations were carried out on the labelled metabolites excreted in the urine and faeces after administration of riboflavin-2-14C.…”