Alterations of specific forms of cytochrome P-450 in rat liver during acute carbon tetrachloride intoxication

Abstract

Male rats were pretreated with phenobarbital, 3-methylcholanthrene, or the corresponding vehicles, administered carbon tetrachloride (CCl 4), and sacrificed 3 hr later. Hepatic microsomes were isolated and assayed for cytochrome P-450 content and mixed-function oxidase activity. The residual content of cytochrome P-450 after CCl 4 intoxication was similar in saline and phenobarbital-pretreated animals. Substantially greater amount of cytochrome P-450 remained in animals pretreated with 3-methylcholanthrene and then challenged with CCl 4. In saline-pretreated animals, the dealkylation of 7-ethoxycoumarin, but not benzphetamine or N,N-dimethylaniline, was decreased following CCl 4 exposure. The enhanced dealkylation following phenobarbital, but not following by 3-methylcholanthrene, was also decreased after CCl 4 poisoning. Microsomes were solubilized with sodium cholate; cytochrome P-450 was partially purified by ω-octylamino Sepharose 4B column chromatography; and cytochrome P-450-containing elements were separated by SDS-polyacrylamide gel electrophoresis. A decrease in the staining intensity of a band migrating with a molecular weight of 51,600 was noted following CCl 4 treatment. Furthermore, the phenobarbital-induced component (MW 51,600), but not that appearing after 3-methylcholanthrene induction (MW 57,900), was also diminished. Microsomal proteins separated by SDS-polyacrylamide gel electrophoresis and stained for heme also showed a decrease in staining which was greater in those microsomal proteins from phenobarbital and saline than in 3-methylcholanthrene-induced animals. The data suggest that a specific cytochrome P-450(s) in the saline-treated animals as well as the cytochrome P-450(s) induced by phenobarbital, but not the 3-methylcholanthrene-induced cytochrome P-450, are susceptible to CCl 4-induced destruction.