Age-related changes in the expression of cytochrome P-450 (b+e) gene in the rat after phenobarbitone administration

Run-on transcription of total RNA and the level of cytochrome P-450 (b+e) mRNA were measured in the liver at different times after administering phenobarbitone (PB) to young (21 wk) and old (120 wk) female rats. Cyto P-450 poly A+ mRNA is stimulated only in the liver and not in brain and kidney. Even though the stimulation of transcription is higher in the young after PB administration, the cytoplasmic RNA peaks earlier in the old. This may be due to faster transport of transcripts from the old nucleus. Furthermore, four P-450 transcripts ranging from 1.5 to 3.0 kb are detected from old nuclear RNA, which possibly represent different stages of processing of its pre-mRNA. These data show that significant changes in the cyto P-450 catalysed reactions may occur in the old liver that may alter its metabolism, especially of steroids.