1-naphthylisothiocyanate-induced elevation of biliary glutathione

1-Naphthylisothiocyanate (ANIT) has been used for many years to study cholangiolitic hepatotoxicity in laboratory animals. Hallmarks of ANIT hepatotoxicity include portal edema and inflammation with bile duct epithelial and hepatic parenchymal cell necrosis. In rats, ANIT hepatotoxicity is dependent upon hepatic glutathione. Studies in vitro have demonstrated that ANIT combines reversibly with glutathione and suggest that intracellular formation and secretion of this glutathione-ANIT conjugate from hepatic parenchymal cells may be responsible for the efflux of glutathione observed upon exposure to ANIT. In vivo, glutathione conjugates produced within hepatic parenchymal cells are typically transported into bile for elimination. Therefore, large concentrations of ANIT in bile may result from hepatic parenchymal cell secretion of a reversible glutathione-ANIT conjugate. To investigate this hypothesis, bile and plasma concentrations of ANIT were determined in rats 1, 4, 8, 12 and 24 hr after administration (100 mg/kg, p.o.). Liver and bile glutathione concentrations were also evaluated. Plasma ANIT concentrations ranged between 2 and 5 microM at 1, 4, 8 and 12 hr and were 0.9 microM at 24 hr after administration. ANIT concentrations in bile at 1, 4, 8 and 12 hr were 60, 28, 21 and 22 microM, respectively. Thus, ANIT was concentrated in bile. Hepatic glutathione was not affected by ANIT during the first 12 hr after administration; however, a moderate elevation occurred by 24 hr. In contrast, a marked elevation in bile glutathione concentration (two times control) occurred 1, 4 and 8 hr after ANIT administration. Thus, the early accumulation of ANIT in bile was coincident with an elevation in bile glutathione. These findings support the hypothesis that glutathione functions to concentrate ANIT in bile. The large concentration of this toxicant in bile may be injurious to bile epithelium, a primary cellular target in ANIT hepatotoxicity.