Short Title: Down-regulation of CYP1A genes by androgen

In Meishan and Landrace pigs, sex-differences in the constitutive expression of hepatic cytochrome P4501A (CYP1A) subfamily enzymes were examined in terms of their mRNA, protein, and activity. All the results from the real-time RT-PCR, Western blotting, and enzyme assays for CYP1A subfamily enzymes indicated that, in 5-month-old Meishan pigs, the expression levels of CYP1A1 and CYP1A2 in males were significantly low as compared with those in females. In contrast, there were no such significant sex-differences in Landrace pigs. Castration of male Meishan pigs led to a female-type expression of the CYP1A subfamily enzymes, whereas no such effect was observed in male Landrace pigs after castration. In both breeds of pigs, the administration of testosterone propionate to the females and castrated males led to marked decreases in the expression levels of mRNAs and proteins in the CYP1A subfamily enzymes, and also in their enzyme activities. Furthermore, the correlation analyses between the serum testosterone level and the gene expression levels of CYP1A subfamily enzymes in different sex-matured (1~5-month-old) male pigs revealed that the clear decrease in expression levels of hepatic CYP1A subfamily enzymes occurred at concentrations of mor