Abstract
In order to know the kinetic aspects of the enterohepatic circulation, the excretion in bile and the elimination from blood of riboflavin were studied in rat. Three riboflavin derivatives, i. e. free riboflavin (FR), flavin-5'-phosphate (FMN), and flavin adenin dinucleotide (FAD) were used. (1) Biliary Excretion 1) Irrespective of the kinds of administered riboflavin derivatives, FR was the major and FAD was the minor excreted in bile, but no FMN was found. 2) A remarkable dose dependency of biliary excretion was found. When high doses (1-10 μmole) were administered, the rapid excretion occurred instantaneously and excretion was proceeded to 80% within 2 hr, and the excretion time course was described with two rate processes of rate constants k1 and k2. On the other hand, when low doses (0.05-0.1 μmole) were administered, the excretion was slow and proceeded to only 50% after 4-5 hr, and the time course was described with one rate process of rate constant k'. It was an interesting result that k' had the similar value to that of k2. 3) Some kinetic model for the dose dependency were discussed. (2) Elimination from Blood 1) FMN and FAD were found to be dephosphorylyzed very rapidly in blood. 2) The elimination of riboflavin from blood after i. v. administered was very fast and obeyed the two compartmental model. 3) The blood concentration time course of i. v. injected riboflavin was compared between a normal and a cannulated rat. The reabsorption of riboflavin could not be ascertained.
