The fate of diastereomeric glutathione conjugates of alpha-bromoisovalerylurea in blood in the rat in vivo and in the perfused liver. Stereoselectivity in biliary and urinary excretion.

The mixture of the two diastereomeric glutathione (GSH) conjugates of alpha-bromoisovalerylurea, (RS)-IU-G, was administered i.v. to anesthetized rats. Bile and urine were collected for 6 hr. Some 70 to 75% was recovered in urine as mercapturates. The half-lives of the urinary excretion were the same for the two mercapturates: 18 min and approximately 130 min, respectively, for the rapid and the slow phase. In bile only 1.5% of the dose of (R) and (S)-IU-G was found; two unidentified metabolites were also found. In rats with ligated kidneys, 4% of the dose of each glutathione conjugate was excreted in bile. Again, the two unidentified metabolites were found. In the isolated recirculating liver perfusion experiments, 1.4% of the administered GSH conjugates was found in bile. The concentration of the GSH conjugates in the perfusion medium remained constant and no other metabolites were formed. When (RS)-alpha-bromoisovalerylurea itself was added to the perfusate, the GSH conjugates in bile increased rapidly. The results show that the GSH conjugate in blood is little excreted in bile due to a slow uptake of the conjugate by the liver. The diastereomeric GSH conjugates show no stereoselectivity in their pharmacokinetics, indicating that the rate limiting step in this process is not stereoselective.