AHR and hydronephrosis: In cultures of murine metanephros, the AHR ligand, benzo(a)pyrene (BaP), disrupted nephrogenesis (Falahatpisheh and Ramos, 2003) and in fetuses from mice fed the AHR ligand 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD, dioxin), hydronephrosis was a common malformation (Peters et al., 1999).