PHENOBARBITAL PRETREATMENT IN-VIVO AND IN-VITRO AND THE EFFECT OF HEPATOTOXICITY OF D-GALACTOSAMINE IN RAT HEPATOCYTES IN CULTURE

Galactosamine (GalN) is a known hepatotoxic compound, acting by deplet ion of uracil nucleotides. The relation between an active cytochrome P -450 system (CYP) and the hepatotoxicity of GalN was studied in rat he patocytes that were pretreated with phenobarbital (PB) in vivo or in v itro. A 24-hr in vitro pretreatment of cultured hepatocytes with PB re sulted in a significant decrease in GalN toxicity as measured by lacta te dehydrogenase (LDH) leakage. Furthermore, GalN treatment resulted i n an increase in the activity of the PB-induced forms of CYP (namely C YP 2B1/2) as measured by 7-pentoxyresorufin O-depentylase (PROD) activ ity. This increase was not found after GalN treatment of microsomes. G alN had no effect on the concentration of the apoenzymes. GalN adminis tration to hepatocytes of in vivo PB-pretreated rats resulted in a sim ilar effect of GalN on the activity of the CYP enzymes but PB in vivo had no effect on GalN toxicity. These results suggest that GalN treatm ent may result in a significant increase in the specific activity of C YP 2B1/2 enzymes (PROD), without an obvious increase in the amount of PB-induced apoenzymes. This phenomenon was measurable only in intact c ells. No direct relation is assumed between the activity of the CYP ap oenzymes and the decrease in GalN toxicity after PB treatment. The tox icity of Gain was inhibited by PB treatment in vitro.