Expression of a constitutive form of cytochrome P450 during rat‐liver development and sexual maturation

Cytochrome P450 cDNA clone designated pP450 IGC 1 has been previously isolated from a phenobarbital-induced rat liver cDNA library, characterized and proven to correspond to a constitutive cytochrome P450 sensitive to phenobarbital stimulation. IGC 1 pDNA, as well as a unique synthetic oligonucleotide probe, were used to investigate the mRNA levels at different developmental stages (fetal, male and female rats of various ages) in parallel with the study of the expression of the liver development and male phenotype markers: albumin, alpha-fetoprotein and alpha 2u globulin mRNAs. Cytochrome P450 IGC 1 mRNA responsiveness to phenobarbital administration was studied in animals of both sexes at different developmental stages. P450 IGC 1 mRNA was not detectable in fetuses nor in male or female rat liver before sexual maturation, becoming elevated at 45 days age, increasing up to 3 months and reaching relatively higher levels in the female liver than in the male. The concentrations of P450 IGC 1 mRNA closely paralleled the increases in alpha 2u globulin mRNA in male liver, as analyzed by dot and Northern blot hybridization. However, P450 IGC 1 was markedly induced by phenobarbital already at 20 days age both in males and females while alpha 2u globulin mRNA was not inducible before sexual maturation. It is concluded that the expression of cytochrome P450 IGC 1 mRNA is associated with the sexual maturation being differently modulated in the male and in the female rat liver. This cytochrome P450 isoenzyme may play an important physiological role in sex differential steroid metabolism and susceptibility to cytotoxic and genotoxic agents.