Constitutive and induced expression by pyridine and beta-naphthoflavone of rat CYP1A is sexually dimorphic.

Adult male and female Sprague-Dawley rats were compared in terms of the constitutive levels and inducibility of CYP1A1 and CYP1A2 (CYP1A) in lung, kidney, and liver. CYP1A were induced by i.p. treatment with pyridine (75 mg/kg per day) or beta-naphthoflavone (betaNF; 25 mg/kg per day) for two consecutive days and analyzed catalytically (via O-dealkylation of resorufin ethers), at the protein level (by Western blot analysis) and at the mRNA level (by Northern blot analysis). In untreated rats. CYP1A1 protein and its mRNA were detectable only in the lung and kidney of females but not males, whereas CYP1A2 protein and its mRNA were detectable only in the liver in either gender. Pyridine treatment upregulated CYP1A1 mRNA and its protein in the lung, kidney and liver in female rats, and upregulated the mRNA but not the protein in the lung and liver in male rats. Conversely, pyridine induced both CYP1A2 mRNA and protein in the liver in female rats, whereas it induced the protein but not its mRNA in the liver in male rats. No gender difference was observed in the plasma elimination rate of administered pyridine. BetaNF, in contrast to pyridine, induced CYP1A proteins, activities, and mRNA to higher levels in male than in female rats. The results show that the constitutive as well as inducible expression of CYP1A is sexually dimorphic in the Sprague-Dawley rat, with females being more responsive than males to induction by pyridine but with males being more responsive than females to induction by betaNF. The findings support the involvement of different mechanisms in CYP1A induction by pyridine and betaNF.