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Role of RNA in induction of hepatic microsomal mixed function oxidases
Abstract:
Induction of hepatic microsomal cytochrome P-450 and ethylmorphine N-demethylase activity by phenobarbital requires de novo synthesis of mRNA. Inhibition of RNA synthesis by alpha-amanitin given up to 8 hr after phenobarbital administration substantially inhibits this induction. However, beyond 8 hr after phenobarbital administration, RNA synthesis is not required for induction of these hepatic microsomal systems. Thus, mRNAs for cytochrome P-450 and ethylmorphine N-demethylase appear to be stable. Furthermore, these experiments reveal that the lag period for RNA synthesis approximates the length of the lag period for induction of the hepatic microsomal enzyme systems.
Insights
Phenobarbital induction of liver enzymes requires new mRNA synthesis initially. After 8 hours, RNA synthesis is not needed, indicating stable messenger RNAs for cytochrome P-450 and ethylmorphine N-demethylase.
Area of Science:
- Biochemistry
- Pharmacology
- Molecular Biology
Background:
- Phenobarbital is known to induce hepatic microsomal enzymes, including cytochrome P-450 and ethylmorphine N-demethylase.
- The precise mechanism and temporal requirements for this induction, particularly the role of messenger RNA (mRNA) synthesis, are not fully elucidated.
Purpose of the Study:
- To investigate the requirement of de novo mRNA synthesis for phenobarbital-induced hepatic microsomal enzyme activity.
- To determine the stability of mRNAs encoding cytochrome P-450 and ethylmorphine N-demethylase.
- To compare the lag periods for RNA synthesis and enzyme induction.
Main Methods:
- Administration of phenobarbital to induce hepatic microsomal enzymes.
- Inhibition of RNA synthesis using alpha-amanitin at various time points post-phenobarbital administration.
- Assay of cytochrome P-450 and ethylmorphine N-demethylase activity.
Main Results:
- Phenobarbital induction of cytochrome P-450 and ethylmorphine N-demethylase activity necessitates de novo mRNA synthesis.
- Inhibition of RNA synthesis up to 8 hours after phenobarbital administration significantly impedes enzyme induction.
- Beyond 8 hours, RNA synthesis is dispensable for enzyme induction, suggesting mRNA stability.
- The lag phase for RNA synthesis correlates with the lag phase for enzyme system induction.
Conclusions:
- Messenger RNAs for hepatic cytochrome P-450 and ethylmorphine N-demethylase are stable.
- The initial phase of phenobarbital-induced enzyme activity relies on the synthesis of new mRNA molecules.
- The temporal relationship between RNA synthesis and enzyme induction highlights the importance of mRNA stability in sustained enzyme expression.