Synergistic interactions of 2,3,7,8-TCDD and 2,2',4,4',5,5'-hexachlorobiphenyl in C57BL/6J and DBA/2J mice: role of the Ah receptor.

Treatment of C57BL/6J mice with 2,2',4,4',5,5'-hexachlorobiphenyl (HCBP, 500 mumol/kg) elevated hepatic cytosolic Ah receptor levels 82-107% for up to 14 days. Scatchard analysis of the [3H]2,3,7,8-TCDD (TCDD)-Ah receptor saturation binding curves from corn oil and HCBP treated rats gave KD values of 0.80 and 0.90 nM, respectively and confirmed that treatment with HCBP did not significantly alter receptor-radioligand affinities. Administration of HCBP to DBA/2J mice did not result in detectable hepatic cytosolic Ah receptor levels. Cotreatment of C57BL/6J mice with HCBP (500 mumol/kg) at a dose level of TCDD (1 nmol/kg) which elicited less than 10% of the maximum induction response resulted in significant synergistic induction of hepatic EROD and AHH [compared to animals treated only with TCDD (1 nmol/kg)]. In contrast, cotreatment of C57BL/6J mice with HCBP (500 mumol/kg) and maximally inducing dose levels of TCDD (100 or 500 nmol/kg) resulted in either a slight or no difference in the induction of AHH or EROD compared to the induction responses observed in mice treated only with TCDD. In contrast, cotreatment of DBA/2J mice with TCDD and HCBP (500 mumol/kg) resulted in significant synergistic induction of AHH and EROD at both submaximal (10-500 nmol/kg) and maximal (5000 nmol/kg) induction levels of TCDD. The only significant interactive effect of HCBP (500 mumol/kg) on the toxicity of TCDD in C57BL/6J and DBA/2J was protection from body weight loss observed after cotreatment of HCBP and TCDD in DBA/2J mice.