Immunohistochemical localization of cytochrome P-450a in liver sections from untreated rats and rats treated with phenobarbital or 3-methylcholanthrene.

Antibodies against cytochrome P-450a purified from hepatic microsomes of Long-Evans rats were used for indirect immunofluorescent localization of cytochrome P-450a within the livers of untreated, phenobarbital-treated, and 3-methylcholanthrene-treated mature and immature male and female rats. Immunohistochemical localization of cytochrome P-450a in liver sections from untreated mature male rats revealed fluorescence primarily in the central and midzonal regions, and moderate fluorescence in the periportal region. This pattern of fluorescence was not significantly altered in liver sections from mature male rats treated with phenobarbital or 3-methylcholanthrene. Liver sections from untreated mature female and immature male and female rats were primarily fluorescent in the central region with weak fluorescence in the midzonal and periportal regions of the lobule. Phenobarbital or 3-methylcholanthrene treatment markedly enhanced the intensity and lobular distribution of the fluorescence in liver sections from mature female and immature male and female rats. The apparent induction of cytochrome P-450a in the mature female and immature male and female rats, but not in mature males, is consistent with our previous immunochemical studies on the quantity of cytochrome P-450a in hepatic microsomes from untreated and treated rats. In addition, this study demonstrates that the lobular distribution of cytochrome P-450a in untreated mature male rats is different from the distribution of cytochrome P-450a in untreated female or immature rats.