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Inductive and repressive effects of rifampicin on rabbit liver microsomal cytochrome P-450
Abstract:
New Zealand White rabbits were treated with rifampicin at a dose of 50 mg/kg for 4 days. The total amount of microsomal hepatic cytochrome P-450 was not modified in treated, with respect to control, animals. However, further studies involving SDS-PAGE analysis, monooxygenase activity measurements and radial immunodiffusion assays indicated that rifampicin strongly affects the level of two P-450 isoenzymes. An LM3 form was induced; this form, apparently associated with erythromycine demethylase activity and hydroxylation of progesterone preferentially in position 6 beta, was shown to be immunologically and functionally different from LM3a and LM3b. On the other hand, an LM4 form, typically induced by beta-naphthoflavone, was repressed. The concomitant inductive/repressive effect of rifampicine on two cytochrome P-450 isoenzymes makes this drug a very atypical inducer, at least in the rabbit.
Insights
Rifampicin treatment in rabbits did not alter total hepatic cytochrome P-450 levels but selectively affected specific isoenzymes. This drug uniquely induces one form while repressing another, making it an atypical inducer.
Area of Science:
- Pharmacology
- Biochemistry
- Drug Metabolism
Background:
- Cytochrome P-450 enzymes are crucial for drug metabolism.
- Understanding how drugs affect specific P-450 isoenzymes is vital for predicting drug interactions and efficacy.
Purpose of the Study:
- To investigate the effects of rifampicin on hepatic cytochrome P-450 isoenzymes in New Zealand White rabbits.
- To characterize the specific isoenzymes affected by rifampicin treatment.
Main Methods:
- Treatment of rabbits with rifampicin (50 mg/kg for 4 days).
- Analysis of microsomal hepatic cytochrome P-450 levels.
- SDS-PAGE, monooxygenase activity assays, and radial immunodiffusion assays.
Main Results:
- Rifampicin did not change total hepatic cytochrome P-450 levels.
- Rifampicin induced an LM3 form with erythromycin demethylase and progesterone 6 beta-hydroxylation activity.
- Rifampicin repressed an LM4 form, typically induced by beta-naphthoflavone.
Conclusions:
- Rifampicin exhibits an atypical inductive/repressive effect on specific cytochrome P-450 isoenzymes in rabbits.
- The observed effects suggest unique mechanisms of drug induction and repression by rifampicin.