Renal transtubular transport of mercapturic acid in vivo

When $\text{S-}\text{benzyl}\text{-N-}\text{acetyl}\text{-}\text{l}\text{-}\text{U}\text{-}{}^{14}\text{C}\text{]}\text{cysteine}$, a mercapturic acid, was administered to rats intravenously, the plasma level of radioactivity decreased very rapidly with a concomitant increase in the renal level of radioactivity. The renal radioactivity reached its maximum within 2 min and then decreased rapidly with concomitant appearance of the radioactive mercapturic acid in the urine. Bilateral ligation of the ureters resulted in only a slight decrease in the rate of disappearance of mercapturic acid from the plasma, while bilateral nephrectomy caused a marked retardation of its clearance from the plasma. Intravenous administration of probenecid, a well known inhibitor of a renal transbular transport system for organic acids, caused a significant retardation of mercapturate clearance from the plasma in both of the control and ureter-ligated animals. The renal accumulation of this mercapturic acid as well as its excretion into urine was inhibited by probenecid.All these data suggested that a mercapturic acid in the plasma was preferentially taken up by renal tubule cells from the basolateral side of plasma membranes via the probenecid-sensitive transtubular transport system and then excreted rapidly into the lumenal space. This transtubular transport of a mercapturic acid seems to constitute an important process in the hepato-renal cooperation in the mercapturic acid biosynthesis in vivo.