CYP1B1 expression in rat testis and Leydig cells is not inducible by aryl hydrocarbon receptor agonists

1. Cytochrome P450 1B1 (CYP1B1) is highly expressed in testis, but there is conflicting information regarding the inducibility of testicular CYP1B1 by aryl hydrocarbon receptor (AhR) agonists. 2. To assess AhR-mediated regulation, testicular CYP1B1 expression was measured following treatment of adult rats with 3-methylcholanthrene and various dosages of benzo[a]pyrene and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). The effect of TCDD on CYP1B1 expression in R2C rat Leydig and MA-10 mouse Leydig cells in culture was also determined. 3. Immunoblot analysis showed that treatment with benzo[a]pyrene at dosages up to 200 mg/kg/day and 3-methylcholanthrene at 25 mg/kg/day did not induce testicular CYP1B1 expression. Treatment with TCDD at dosages of 1, 5 or 100 microg/kg had no effect, but testicular CYP1B1 protein levels were increased by approximately 50% at dosages of 10 and 50 microg/kg. 4. CYP1B1 mRNA levels in MA-10 and CYP1B1 protein levels in R2C cells were not induced by exposure to TCDD (10-1000 nM). 5. Overall, the results indicate that rodent testicular CYP1B1 is not inducible by AhR agonists.