HEAVY-METAL INHIBITION OF EROD ACTIVITY IN LIVER-MICROSOMES FROM THE BASS DICENTRARCHUS-LABRAX EXPOSED TO ORGANIC XENOBIOTICS - ROLE OF GSHIN THE REDUCTION OF HEAVY-METAL EFFECTS

In vitro effects of Cu2+, Hg2+ and of CH3Hg+ on fish liver microsomal EROD activity have been studied. Liver microsomes from the fish Dicent rarchus labrax, treated with beta-naphthoflavone (50 mg/kg) or benzo-a -pyrene (20 mg/kg), showed a 4 to 15-fold increase of EROD activity. A ddition to the reaction mixture of nmolar concentrations of Cu2+, Hg2 and CH3Hg+ significantly decreased EROD activity, micromolar concentr ations totally inhibited the enzyme, while treatments with mixtures of nanomolar Cu2+, Hg2+ and CH(3)Ng(+) exerted an additive inhibitory ef fect. Addition of physiological concentrations of GSH drastically redu ced the heavy metal inhibitory effects. These results demonstrate that fish liver EROD activity is highly sensitive to extremely low concent rations of heavy metals, also suggesting that GSH plays a fundamental role as a first-line defense against heavy-metal cytotoxicity. (C) 199 7 Elsevier Science Ltd.