EFFECT OF PYRAZOLE AND DEXAMETHASONE ADMINISTRATION ON CYTOCHROME-P450 2E1 AND 3A ISOFORMS IN RAT-LIVER AND KIDNEY - LACK OF SPECIFICITY OFP-NITROPHENOL AS A SUBSTRATE OF P450 2E1

The induction effects of pyrazole and dexamethasone (known to be speci fic to P450 2E1 and 3A enzymes, respectively), given alone or simultan eously, were studied in rat liver and kidney microsomes. Pyrazole trea tment induced the catalytic activity and the amount of P450 2E1 enzyme in both organs. Immunoreactive P450 2E1 and 4-nitrophenol 2-hydroxyla tion increased 8- and 13-fold, respectively (versus control), in the k idney, but only 2.4- and 2.7-fold (versus control) in the liver after pyrazole treatment. As assessed by nifedipine oxidation activity dexam ethasone treatment increased the P450 3A catalytic activity approximat ely 4-fold (versus control) in the liver, but not in the kidney, sugge sting that P450 3A was not inducible in the kidney. Pyrazole decreased P450 3A activity in the liver but did not modify it in the kidney. A combination of both chemicals induced both enzymes, but to a lesser ex tent than treatment with each single chemical compound. Furthermore, t he P-hydroxylation of p-nitrophenol, considered one of the most specif ic substrates for monitoring the level of P450 2E1, was mediated also by P450 3A, at least in dexamethasone-treated rats. Finally, this expe rimental work demonstrated that P450 3A induction is organ-specific, a nd it also demonstrated the lack of specificity of p-nitrophenol as a P450 2E1 substrate.