RESPONSE OF HEPATIC XENOBIOTIC-METABOLIZING ENZYMES IN RAINBOW-TROUT (ONCORHYNCHUS-MYKISS) AND COD (GADUS-MORHUA) TO 2,3,7,8-TETRACHLORODIBENZO-P-DIOXIN (2,3,7,8-TCDD)

2,3,7,8-Tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD) was administered in tragastrically twice with 4 days interval, to juvenile cod and rainbow trout, total dose 8 mug/kg body weight. Fish were killed after 9 and 17 days and the effects on hepatic xenobiotic metabolizing enzymes wer e determined by examining aldrin epoxidase (AE), glutathione-S-transfe rase (GST) against 1-chloro-2,4-dinitrobenzene (CDNB) and the cytochro me P450-dependent ethoxyresorufin-O-deethylase (EROD) activities, and by immunoquantitating cytochrome P4501A1 using an indirect enzyme-link ed immunosorbent assay (ELISA). AE and GST activities were not induced . However, 2,3,7,8-TCDD significantly induced EROD activities in rainb ow trout and cod to 1450% and 415%, respectively, of the corresponding controls 9 days after the first treatment. The increase in EROD activ ity was supported by induction of the main catalyst P4501A1 as reveale d by ELISA analyses. The distribution pattern of C-14-labelled 2,3,7,8 -TCDD was studied by whole-body autoradiography. The liver concentrati on of radiolabelled compound in cod exceeded that of the rainbow trout . However, the degree of hepatic enzyme induction did not correspond t o the concentration of radiolabelled 2,3,7,8-TCDD in the liver. Despit e of the substantially higher level of 2,3,7,8-TCDD in the liver of co d, the EROD induction was lower in this species compared to rainbow tr out.