Pyridine induction of cytochrome P-450 in the rat: role of P-450j (alcohol-inducible form) in pyridine N-oxidation.

Previous research has shown that pyridine (PY) pretreatment of rabbits elevates total hepatic microsomal cytochrome P-450 content in association with the appearance of intense bands in the region of P-450LM4 and LM3 in the electrophoretic pattern of the microsomes and increased rates of PY N-oxide production and N-nitrosodimethylamine, alcohol and aniline metabolism. In the present study, PY administration (100 mg/kg i.p., 4 days) to rats was found to elevate hepatic microsomal cytochrome P-450 content approximately 2.5-fold as compared to controls. Sodium dodecylsulfate-polyacrylamide gel electrophoresis revealed a protein band of enhanced intensity migrating in the region of P-450j, the major ethanol-inducible form of rat liver cytochrome P-450. Immunochemical analysis confirmed that the level of immunoreactive P-450j protein was increased in PY-induced microsomes as compared to preparations from control, phenobarbital- or beta-naphthoflavone-induced animals. The rate of PY N-oxide production was enhanced 4-fold in PY-induced microsomes relative to untreated controls and was approximately 1.5- to 2-fold greater than that monitored for either phenobarbital- or beta-naphthoflavone-induced microsomes. When data were normalized for increased P-450 content, an altered substrate specificity was suggested for the PY-induced microsomes. para-Nitrophenol hydroxylase activity, which is exhibited primarily by the ethanol-inducible form of P-450, was elevated approximately 4-fold in PY-induced microsomes relative to uninduced microsomes and, when expressed per nanomol of P-450, was approximately 2- to 3-fold greater in PY-induced preparations as compared to phenobarbital-, beta-naphthoflavone-induced, or uninduced microsomes.(ABSTRACT TRUNCATED AT 250 WORDS)