Glutathione metabolism in hepatomous liver of rats treated with diethylnitrosamine

Abstract

Glutathione metabolism was studied in rat liver during diethylnitrosamine (DEN) carcinogenesis. Some studies were also made in foetal rat liver. Endogenous GSH and non-protein thiols concentrations are increased in DEN-treated rats when compared to non-treated rats but no differences were found in cysteine, total thiols and protein thiols concentration. In foetal liver GSH concentration is only 35% of that in DEN-treated rat liver. The activities of several enzymes involved in glutathione metabolism are changed in DEN-treated rats. γ-Glutamyl transferase activity and cysteine formation from GSH by liver homogenates is increased sevenfold. γ-Glutamylcysteine synthetase activity, initial rate of [ 35S]cysteine incorporation in γ-glutamylcysteine and initial rate of GSH formation from [ 35S]cysteine are increased two-fold. Cytosolic GSH S-transferase activity is increased twofold in DEN-treated rats and so GSH S-conjugates concentration is probably also increased. In foetal rat liver γ-glutamyl transferase activity is about the same but γ-glutamylcysteine synthetase activity is only 10% of that in DEN-treated rat liver. The increased GSH concentration in DEN-treated rat liver is probably due to the simultaneous increase in the activities of γ-glutamyl transferase and γ-glutamylcysteine synthetase. Blood plasma total glutathione is increased 1.4 times in DEN-treated rats, but no differences are found in GSH hepatic arteriovenous gradient. This associated with the increased γ-glutamyl transferase activity suggests that sinusoidal GSH efflux is increased in DEN-treated rats.