Rat liver microsomal induction of the oxidation of drugs and alcohols, and sodium dodecyl sulfate-gel profiles after in vivo treatment with pyrazole or 4-methylpyrazole

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Studies were carried out to characterize and compare the effects of pyrazole and 4-methylpyrazole, potent inhibitors of alcohol dehydrogenase, on microsomal oxidation of a variety of drugs and alcohols. Whereas pyrazole treatment of rats (200 mg/kg b.wt./day for 2 days) resulted in an enrichment of a cytochrome P-450 isozyme with a molecular weight of about 52,000 on sodium dodecyl sulfate gels, 4-methylpyrazole treatment resulted in increased amounts of two or three P-450 isozymes, one of which appeared to be similar to the isozyme increased by pyrazole. The qualitative induction of two or three isozymes of P-450 as shown by sodium dodecyl sulfate-gel electrophoresis correlates with a 2-fold increase in total content of P-450 by 4-methylpyrazole. Microsomes from the pyrazole-treated rats displayed increased activity (expressed per milligram of protein or per nanomole of P-450) with aniline, p-nitroanisole, dimethylnitrosamine (low-K(m) enzyme) and ethanol as substrates, but not with aminopyrine, ethoxycoumarin or dimethylnitrosamine (high-K(m) enzyme). A stereochemical preference for the (+)-2-butanol isomer over the (-)-isomer was also observed. Kinetic experiments indicated that the pyrazole treatment increased the V(max) for ethanol, aniline and (+)-2-butanol oxidation. These properties are similar to those found with microsomes from chronic ethanol-fed rats and suggest that, in rats, pyrazole and ethanol may induce similar isozymes of P-450, and that the former may serve as a convenient model for the latter. This comparable induction between ethanol and pyrazole is in contrast to results using imidazole, which has been reported by others not to induce an alcohol-preferring P-450 in rats. 4-Methylpyrazole treatment resulted in an increase in the oxidation of all the drugs and alcohols tested, primarily due to the increase in content of P-450. Analogous to results with pyrazole, 4-methylpyrazole treatment also resulted in a stereochemical preference for the (+)-isomer over the (-)-isomer in the oxidation of 2-butanol and increased turnover numbers with aniline and p-nitroanisole. However, in contrast to pyrazole, no increase in turnover number with ethanol, (+)-2-butanol or dimethylnitrosamine (low-K(m) enzyme) was found after 4-methylpyrazole treatment. It is probable that these divergent effects can be related to the induction of two or three different P-450 isozymes by 4-methylpyrazole, with the 52,000 MW isozyme showing properties of an alcohol-preferring isozyme, whereas the other isozymes show good activity with aniline or p-nitroanisole but not with alcohols. Thus, there are similarities as well as differences in the interaction of pyrazole and 4-methylpyrazole with rat liver microsomes, and some of these interactions are identical to those found after chronic ethanol treatment.

Original languageEnglish
Pages (from-to)1012-1019
Number of pages8
JournalJournal of Pharmacology and Experimental Therapeutics
Issue number3
StatePublished - 1986


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