Effect of TCDD treatment on hepatic mRNA levels for constitutive P450s and POR in wild-type and Ahr −/− mice. Real-time quantitative RT-PCR analysis of mRNA levels for (A) CYP2D9, (B) CYP3A11 and (C) POR, relative to β-actin. Results are expressed as a percentage of the mean for the vehicle-treated wild-type mice. Data are expressed as mean ± SD of determinations from six wild-type mice per group and three Ahr −/− mice per group. Data were analyzed initially using a randomized-design two-way ANOVA and the P values for the main effects are reported here: CYP2D9 (treatment, P = 0.1177; genotype, P = 0.0022; interaction, P = 0.0597), CYP3A11 (treatment, P = 0.0031; genotype, P < 0.0001; interaction, P = 0.7639), and POR (treatment, P = 0.4288; genotype, P < 0.0001; interaction, P = 0.0298). Planned comparisons to identify significant differences between particular groups utilized a post test Bonferroni-corrected for multiple comparisons. *, significantly different (P < 0.05) from genotype-matched vehicle control mice; †, significantly different (P < 0.05) from treatment-matched wild-type mice.