Related Experiment Videos
Metabolism of methamphetamine, amphetamine and p-hydroxymethamphetamine by rat-liver microsomal preparations in vitro
Abstract:
Methamphetamine N-demethylation and p-hydroxylation activities of rat liver were located mainly in the microsomal fraction. The Km values for methamphetamine and p-hydroxymethamphetamine demethylations were 1.0 and 1.6 mM, respectively. The Km value for amphetamine p-hydroxylation was 10.2 microM; substrate inhibition occurred at high substrate concn. Two Km values were obtained for the aromatic hydroxylation of methamphetamine (10.6 microM and 2.2 mM). N-Demethylation of methamphetamine and p-hydroxymethamphetamine were depressed in rats pretreated with 3-methylcholanthrene, CoCl2 or SKF 525-A. In rats pretreated with phenobarbital, methamphetamine demethylase was induced and p-hydroxymethamphetamine demethylase was depressed. The p-hydroxylation of methamphetamine and amphetamine in rats pretreated with phenobarbital, CoCl2, SKF 525-A or iprindole were depressed.
Insights
Rat liver enzymes in the microsomal fraction metabolize methamphetamine via N-demethylation and p-hydroxylation. Enzyme activity was altered by various pretreatments, affecting methamphetamine metabolism.
Area of Science:
- Pharmacology
- Biochemistry
- Drug Metabolism
Background:
- Methamphetamine is a widely abused stimulant with complex metabolic pathways.
- Understanding its metabolism is crucial for developing effective treatments and interventions.
Purpose of the Study:
- To investigate the specific enzymes responsible for methamphetamine N-demethylation and p-hydroxylation in rat liver.
- To characterize the kinetic properties (Km values) of these metabolic reactions.
- To examine the effects of various enzyme inducers and inhibitors on methamphetamine metabolism.
Main Methods:
- Microsomal fractions from rat liver were used to assay N-demethylation and p-hydroxylation activities.
- Kinetic parameters (Km values) were determined for methamphetamine and its metabolites.
- Enzyme activity was measured in rats pretreated with compounds like 3-methylcholanthrene, CoCl2, SKF 525-A, and phenobarbital.
Main Results:
- Methamphetamine N-demethylation and p-hydroxylation primarily occur in the rat liver microsomal fraction.
- Specific Km values were determined for methamphetamine and p-hydroxymethamphetamine demethylations, and amphetamine p-hydroxylation.
- Aromatic hydroxylation of methamphetamine exhibited two distinct Km values.
- Pretreatment with 3-methylcholanthrene, CoCl2, or SKF 525-A decreased N-demethylation and p-hydroxylation.
- Phenobarbital induced methamphetamine demethylase but depressed p-hydroxymethamphetamine demethylase.
- Phenobarbital, CoCl2, SKF 525-A, and iprindole all depressed the p-hydroxylation of methamphetamine and amphetamine.
Conclusions:
- Rat liver microsomes contain key enzymes for methamphetamine metabolism.
- Enzyme induction and inhibition significantly alter methamphetamine metabolic pathways.
- These findings provide insights into factors influencing methamphetamine's pharmacokinetic profile and potential drug interactions.