4-HYDROXYPYRAZOLE: EFFECT ON GLUTATHIONE LEVELS AND ON THE INCORPORATION OF L-[U-14C]VALINE INTO PROTEIN IN ISOLATED RAT HEPATOCYTES

Abstract

Isolated rat hepatocyles (8-12×106 cells/ml) were incubated in Waymouth's medium in the presence of L-[U-14C]valine(0.01 μCi/ml). Valine incorporation into protein as well as the total amount of glutathione (reduced and oxidized) in the cell suspension were determined after 1, 2 and 3 hr of incubation. When incubated for 3 hr, 4-hydroxypyrazole (0.5 and 1 mM) decreased (by about 20% and 40% respectively) valine incorporation into cellular as well as into secreted protein. The increment in glutathione level during incubation (3 hr) of hepatocytes was decreased by 35% when 4-hydroxypyrazole (1 mM) was present in the incubation medium. Such a change was found to be neither ATP-dependent nor associated with malonaldehyde production or cellular leakage. Pyrazole at a high concentration (10 mM) decreased the rate of valine incorporation into protein by 20% only, while the level of glutathione remained unchanged. These results suggest that the inhibition of protein biosynthesis after administration of the alcohol dehydrogenase inhibitor pyrazole to rats may be mediated by 4-hydroxypyrazole and that the decrease in glutathione level caused by 4-hydroxypyrazole could contribute to the hepatotoxicity of this latter compound.