RELATIVE POTENCIES OF POLYCHLORINATED DIBENZO-P-DIOXINS (PCDDS), DIBENZOFURANS (PCDFS) AND BIPHENYLS (PCBS), FOR CYTOCHROME-P450 1A INDUCTION IN THE MIRROR CARP (CYPRINUS-CARPIO)

Carp received a single i.p. dose of 2,3,7,8-TCDD, 2,3,7,8-TCDF, 1,2,3,7,8-PnCDD, 2,3,4,7,8-PnCDF, 1,2,3,6,7,8,-HxCDD, OCDF, OCDD, 2,3',4,4',5-PCB (PCB 118), 3,3',4,4',5-PCB (PCB 1 26) or 2,2',4,4,5,5'-PCB (PCB 153). Four doses per congener were used increasing by a factor five. Fish were sacrificed after 2 weeks and hepatic cytochrome P450 IA protein content (P450 IA), 7-ethoxyresorufin-0-deethylation (EROD) activity and hepatic concentrations of the inducing compounds were determined. The aim of this study was to determine the relative, P450 IA-inducing potencies (RP) of several PCDDs, PCDFs and PCBs, relative to 2,3,7,8-TCDD. RPs were calculated based on ED50s derived from the administered doses or hepatic concentrations for induction of EROD or P450 IA protein levels. The RPs (molar ED50 TCDD/molar ED50 congener), based on EROD induction and internal concentration, for 2,3,7,8-TCDF, 1,2,3,7,8-PnCDD, 2,3,4,7,8-PnCDF and 1,2,3,6,7,8-HxCDD were 0.03, 0.68, 0.36 and 0.59, respectively. The RPs of PCB 118 and PCB 126 were estimated to be 0.0004 and > 0.005, respectively. No RP could be calculated for OCDD and PCB 153, due to the absence of P450 1 A induction by these congeners. PnCDD appeared to be the most potent inducer of hepatic P450 IA. A statistically significant EROD induction was already effected by a concentration of 63.75 pg PnCDD/g liver, which was in the present study the lowest effective concentration of all congeners.