Mdr1a.fLUC is inducible by TCPOBOP regardless of PXR status. (A) pxr+/+ (WT) and pxr−/− (KO) mice that were heterozygous for the mdr1a.fLuc allele were given TCPOBOP (3 mg/kg) or corn oil (Veh) by i.p. injection at times 0, 72, and 144 hours after the initial TCPOBOP injection, as indicated by the dashed arrows. Results are from a single representative experiment. Luminescence was quantified as in Fig. 1. (B–D) Normalized luminescence intensities at the 8-hour time points after each dosing cycle. Data for all mice from one single-dosing experiment (included in dose 1 only) and two multidosing experiments (doses 1–3) are pooled and averaged (± S.E.M.). Panels show comparisons as in Fig. 1. WT + TCPOBOP (n = 38 for dose 1, n = 26 for doses 2 and 3), KO + TCPOBOP (n = 39 for dose 1, n = 27 for dose 2, and n = 25 for dose 3), WT + Veh (n = 39 for dose 1, n = 27 for dose 2, and n = 26 for dose 3), KO + Veh (n = 38 for dose 1, n = 26 for dose 2, and n = 25 for dose 3). *P ≤ 0.05; **P ≤ 0.01; ***P ≤ 0.001; ****P ≤ 0.0001.