Induction of cytochrome P-450 by phenobarbital is mediated at the level of transcription.

We have previously shown that the 43-fold induction by phenobarbital of the major phenobarbital-inducible cytochrome P-450 of rat liver microsomal membranes (PB P-450) is mediated by a 20-fold increase in the amount of its mRNA in the cytoplasm. Here we demonstrate that the induction of the mRNA can be almost entirely accounted for by an increase in the rate of transcription of genes coding for PB P-450, and involves little or no change in the rates of processing, transport or degradation of the mRNA. Phenobarbital treatment resulted in no amplification or rearrangement of PB P-450 genes.