Expression of cytochrome P450 in LEC rats during the development of hereditary hepatitis and hepatoma.

The expression of 14 forms of cytochrome P450 in the liver as well as changes in the testosterone hydroxylation activities of hepatic microsomes were investigated during the development of hepatitis in Long-Evans Cinnamon (LEC) rats. P4501A1 and -1A2 (3-methylcholanthrene-inducible forms) and P4502B1 and -2B2 (phenobarbital-inducible forms) were barely detected in the hepatic microsomes of male and female LEC rats. In immature male rats, the levels of male-specific forms (P4502C11 and -2C13) were higher in LEC rats than in control Long-Evans Agouti (LEA) rats. P4502C11 appeared in female LEC rats from 4 to 16 weeks of age, reflecting that testosterone 2 alpha- and 16 alpha-hydroxylation activities were detected at significant levels in female LEC rats. In immature female rats, the level of P4502C12 (a major female-specific form) was higher in LEC rats than in LEA rats. The level of P4502C13 in male LEC rats and that of P4502C12 in female LEC rats decreased markedly with ageing or during the development of hepatitis. The level of P4503A2 (a male-predominant form) was especially high in immature male and female LEC rats, reflecting that both rats had high 2 beta- and 6 beta-hydroxylation activities toward testosterone. These sex-specific forms are regulated by androgens and by pituitary growth hormone. Thus, there may be abnormalities of the hypothalamo-pituitary-gonadal axis in LEC rats. Furthermore, P4503A2 efficiently activates aflatoxin B1, a potent hepatocarcinogen, and the increased levels of this form in LEC rats may be related to the onset of hepatitis or liver cancer.