Depletion of sinusoidal endothelial cell glutathione (GSH) has been proposed as a common mechanism leading to hepatic veno-occlusive disease (HVOD). This study examines whether intraportal infusion of GSH can prevent HVOD in the monocrotaline rat model. HVOD was induced in rats with monocrotaline 160 mg/kg i.g. on day 0. GSH was infused intraportally by mini-osmotic pump. Monocrotaline decreased GSH in sinusoidal endothelial cells, but not in liver homogenate. Infusion of GSH, 2 mol/hr starting day ฯช 1, prevented the decrease in sinusoidal endothelial cell GSH and protected against histological and clinical evidence of HVOD. Protection by GSH was dose-dependent (0.5-2 mol/hr). In rats receiving continuous GSH infusion, treatment with buthionine sulfoximine starting day ฯช 2 decreased sinusoidal endothelial cell GSH and attenuated the protective effect of GSH against monocrotaline. GSH infusion starting 24 hours after monocrotaline (''glutathione rescue'') offered substantial protection to most rats. N-acetyl-Lcysteine conferred protection, but N-acetyl-D-cysteine (an antioxidant that is not a precursor for GSH) had little or no protective effect, and 4-hydroxy TEMPO, a free radical scavenger, was not protective. Discontinuation of the GSH infusion 5 days after monocrotaline administration led to severe hepatic venoocclusive disease on day 6. In conclusion, monocrotaline selectively depletes sinusoidal endothelial cell GSH. Intraportal infusion of GSH protects against monocrotaline toxicity, at least partially by maintaining sinusoidal endothelial cell GSH levels. Glutathione infusion started after monocrotaline is partially protective. Monocrotaline induces prolonged changes in the liver that remain suppressed as long as GSH is infused. (HEPATOLOGY 2000;31:428-434.