Growth hormone regulation of the cytochrome P-450IIC subfamily in the rat: inductive, repressive, and transcriptional effects on P-450f (IIC7) and P-450PB1 (IIC6) gene expression.

The effects of growth hormone (GH) on two constitutively expressed rat liver cytochrome P-450 (P-450) enzymes, namely P-450f (IIC7) and P-450PB1 (IIC6), have been investigated. Hypophysectomy of both male and female rats results in low expression of P-450f. Single daily injections of GH cannot restore expression of P-450f but further repress it. Continuous administration of GH, on the other hand, increases expression of P-450f to levels comparable to those of the normal male and female rat. P-450PB1 is minimally affected by hypophysectomy or GH treatment, although a weak but significant repression by continuous administration of GH can be detected. Run-on analysis shows that continuous GH treatment increases transcription of P-450f. In addition, the sequence of the 5' flanking region of this gene reveals DNA segments that might have a putative role in the transcriptional regulation of P-450f by GH.