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Phenobarbital-inducible gene expression in developing rat liver: relationship to hepatocyte function.
1INSERM U 75, CHU Necker, Paris, France.
Biochimica Et Biophysica Acta
|December 22, 1989
Summary
The number of liver cells, not biochemical changes, controls how phenobarbital-inducible genes are expressed during development. This study shows phenobarbital-inducible cytochrome P-450 and UDP-glucuronosyltransferase RNAs are mainly regulated by hepatocyte proliferation.
Area of Science:
- Biochemistry
- Developmental Biology
- Pharmacology
Background:
- Cytochromes P-450 and UDP-glucuronosyltransferases are crucial for drug metabolism.
- Their developmental expression and induction patterns in rat liver are not fully understood.
- Understanding these processes is key to predicting drug efficacy and toxicity during development.
Purpose of the Study:
- To investigate the developmental expression of specific drug-metabolizing enzyme RNAs in rat liver.
- To determine the influence of different chemical inducers on these RNA levels during ontogenesis.
- To elucidate the primary regulatory mechanism controlling phenobarbital-inducible gene expression in developing liver.
Main Methods:
- Quantitative analysis of RNA expression for cytochrome P-450 and UDP-glucuronosyltransferase.
- Administration of various inducers (phenobarbital, pregnenolone 16 alpha-carbonitrile, methylcholanthrene, clofibrate) to rats at different developmental stages.
- Correlation of RNA expression levels with hepatocyte cell number and other developmental parameters.
Main Results:
- RNAs for inducible enzymes were present in fetal liver and stable in non-induced animals.
- Inducers showed differential effects: methylcholanthrene was active in fetal liver, clofibrate had no effect.
- Phenobarbital induction increased with ontogenesis, paralleling hepatocyte proliferation.
- Phenobarbital's induction of P-450 and UDPGT RNAs is restricted to hepatocytes and constant throughout development.
- Phenobarbital potentiated methylcholanthrene's induction capacity exclusively in hepatocytes.
- Pregnenolone 16 alpha-carbonitrile was effective in fetal/neonatal rats, with peak effect at 5 days.
Conclusions:
- Hepatocyte number, not biochemical maturation, controls phenobarbital-inducible gene expression during rat liver development.
- This study provides direct evidence for proliferation-dependent regulation of drug-metabolizing enzymes.
- Pregnenolone 16 alpha-carbonitrile exhibits a distinct temporal regulation compared to phenobarbital.