EFFECTS OF NON-ORTHO-SUBSTITUTED POLYCHLORINATED-BIPHENYLS (CONGENER-77 AND CONGENER-126) ON CYTOCHROME-P4501A AND CONJUGATION ACTIVITIES IN RAINBOW-TROUT (ONCORHYNCHUS-MYKISS)

Immature rainbow trout (Oncorhynchus mykiss) in two separate experimen ts received a single intraperitoneal injection of 0.1, 1 and 5 mg/kg o f either 3,3',4,4'-tetra- or 3,3',4,4',5-pentachlorobiphenyl (IUPAC co ngeners 77 and 126, respectively). The experiments were run at water t emperatures of 6 degrees C and 4 degrees C. Fish were killed 6 days af ter the injection. Biotransformation enzyme activities and cytochrome P4501A (CYP1A) amount and occurrence in different tissues were assayed . Congeners 77 and 126 strongly induced 7-ethoxyresorufin O-deethylase (EROD) and benzo(alpha)pyrene hydroxylase (AHH) activities in liver a nd kidney of rainbow trout. The induction of these cytochrome P4501A d ependent monooxygenases was dose-related especially with congener 77 i n the kidney. However, in the liver the highest dose of both congeners and in kidney the highest dose of congener 126 did not increase the c atalytic monooxygenase activities as much as would have been expected based on the responses obtained with the lower doses. This may be beca use the monooxygenase activities already had attained their maximal in duction capacity at 1 mg/kg dose of each congener. The PCB residues in liver were also determined and found to be highest after 5 mg/kg inje ctions (610 mu g/kg wet weight with congener 77 and 220 mu g/kg with c ongener 126). When cytochrome P4501A protein content was measured, the induction of cytochrome P4501A was still on the increase even in thos e cases where catalytic activity failed to show any further induction. Immunohistochemical samples from liver, kidney and intestine showed c ytochrome P4501A staining which strongly correlated with cytochrome P4 501A in microsomes. Such observations suggest that the amount and occu rrence of P4501A in the tissues can express the induction even when ca talytic activities seem to be suppressed. With respect to enzymes medi ating conjugation reactions, hepatic and renal UDP-glucuronosyltransfe rase (UDP-GT) activities showed elevated levels especially with the 1 and 5 mg/kg doses of both congeners. Glutathione S-transferase (GST) a ctivities did not show such a clear trend. Congeners 77 and 126 prefer entially affected the P4501A enzymes but to some extent also conjugati on activities.