The placenta plays a vital role in maintenance of pregnancy and is able to metabolize many foreign chemical compounds by cytochrome P450 (CYP) system. It is very important to clarify the expression of CYPs in the rat placenta, because rats are frequently and widely use in the embryo- and feto-toxicity studies on foreign chemical compounds. In this study, we investigated the changes in the expression and localization of CYPs protein in the placenta of F344 rats at 9, 11, 13, 16 and 19 days of gestation by Western blot analysis and immunohistochemical staining. Among nine isozymes examined (CYP1A1, 2B1, 2C6, 2C12, 2D1, 2D4, 2E1, 3A1 and 4A1), only CYP3A1 was clearly detected by Western blot analysis at all days of gestation examined. Immunohistochemically, the cytoplasm of giant cells in the trophoblastic region was positively stained by anti-CYP3A1 antibodies. These results suggest that CYP3A1 may be a major component of CYP system in the rat placenta.
