Effects of two hexachlorobiphenyl isomers on ornithine decarboxylase induction: inhibitory effects correlate with aryl hydrocarbon hydroxylase activity.

The effects of 2,2',4,4',5,5'-hexachlorobiphenyl (2,4,5-HCB) or 3,3',4,4',5,5'-hexachlorobiphenyl (3,4,5-HCB) on hepatic ornithine decarboxylase (ODC) induction by dexamethasone were investigated. At one week after a single i.p. dose of corn oil or 2,4,5,-HCB and 4 h after administration of dexamethasone, rats exhibited 50- to 60-fold increases of ODC activity. However, rats that had received 3,4,5-HCB in place of 2,4,5-HCB exhibited only a 8-fold increase in ODC activity in response to dexamethasone administration. 2,4,5-HCB administration resulted in increased hepatic aryl hydrocarbon hydroxylase (AHH) activity. Administration of 3,4,5-HCB produced increased AHH activity and decreased N-demethylase activity. It is suggested that the ODC-inhibitory effects may have resulted from Ah-receptor-mediated events.