Effect of phenobarbital treatment on carbon tetrachloride-mediated cytochrome P-450 loss and diene conjugate formation.

The effect of phenobarbital treatment on the linkage between carbon tetrachloride-mediated cytochrome P-450 loss and lipid peroxidation in rat liver microsomes was studied. Male Sprague-Dawley rats, pretreated with 3 daily i.p. doses of phenobarbital (50 mg/kg) or saline, were orally dosed with carbon tetrachloride (0.01-2.5 ml/kg), with liver microsomes prepared at 7.5-180 min after carbon tetrachloride treatment. In vivo cytochrome P-450 loss displayed pseudo-first-order kinetics, and the initial rates of diene conjugate formation were saturable with dose. Phenobarbital pretreatment decreased the in vivo t0.5,max from 27.0 to 15.6 min, and increased the Kd,app from 0.78 to 1.30 ml/kg for carbon tetrachloride mediated cytochrome P-450 loss. Phenobarbital had no effect on the in vivo Vmax (1.03 to 1.04 delta OD232 nm/min/mg phospholipid) for carbon tetrachloride mediated diene conjugate formation, but decreased the Km,app from 0.22 to 0.10 ml/kg. These results are consistent with destruction of cytochrome P-450 heme resulting from a metabolite which does not leave the site of generation, and with phenobarbital pretreatment enhancing the initiation of lipid peroxidation.