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Differential effects of aging on hepatic microsomal monooxygenase induction by phenobarbital and beta-naphthoflavone
Abstract:
The influence of aging on hepatic microsomal monooxygenase induction by phenobarbital (PB) or beta-naphthoflavone (BNF) was investigated in male Fischer 344 rats maintained in a constant environment. PB-induced increases in microsomal cytochrome P-450 content and NADPH-cytochrome c reductase activity were similar in rats aged 3-5 months (young-adult) and 24-25 months (old), but increased in benzephetamine N-demethylase activity were markedly diminished in the old rats. Separation of hepatic microsomal proteins by sodium dodecylsulfate gel electrophoresis demonstrated that aging decreased the induction by PB of a polypeptide with a molecular weight of 52,500. BNF-induced increases in microsomal cytochrome P-450 and nitroanisole O-demethylase activity were greater in old than in young-adult rats, and BNF induction of 55,000 and 57,000 molecular weight microsomal polypeptides was increased slightly in livers from old rats. The results indicate that age-related effects on monooxygenase induction vary with different inducers of the hepatic microsomal enzyme system.
Insights
Aging affects how the liver responds to drugs differently depending on the substance. While some liver enzyme activities remained similar, others were significantly altered in older rats, impacting drug metabolism.
Area of Science:
- Pharmacology
- Gerontology
- Biochemistry
Background:
- Hepatic microsomal monooxygenases are crucial for drug metabolism.
- Aging can alter the expression and activity of these enzymes.
- Understanding age-related changes in enzyme induction is vital for drug safety and efficacy.
Purpose of the Study:
- To investigate the influence of aging on hepatic microsomal monooxygenase induction by phenobarbital (PB) and beta-naphthoflavone (BNF).
- To determine how age affects the induction of specific enzyme activities and protein expression in rat liver microsomes.
Main Methods:
- Male Fischer 344 rats of different age groups (young-adult vs. old) were treated with PB or BNF.
- Hepatic microsomal enzyme activities (cytochrome P-450 content, NADPH-cytochrome c reductase, benzphetamine N-demethylase, nitroanisole O-demethylase) were measured.
- Microsomal proteins were analyzed using sodium dodecylsulfate gel electrophoresis to assess polypeptide induction.
Main Results:
- PB-induced increases in cytochrome P-450 and NADPH-cytochrome c reductase were similar in young and old rats.
- PB-induced benzphetamine N-demethylase activity and the induction of a 52,500 MW polypeptide were diminished in old rats.
- BNF-induced cytochrome P-450 and nitroanisole O-demethylase activities were greater in old rats.
- BNF induction of 55,000 and 57,000 MW polypeptides was slightly increased in old rats.
Conclusions:
- Age-related effects on hepatic monooxygenase induction are dependent on the specific inducer.
- Aging differentially impacts the induction of various enzyme activities and protein profiles in the liver.
- These findings highlight the complexity of age-associated changes in drug-metabolizing enzymes.