EFFECTS OF PIPERONYL BUTOXIDE AND BETA-NAPHTHOFLAVONE ON CYTOCHROME P4501A EXPRESSION AND ACTIVITY IN ATLANTIC SALMON (SALMO-SALAR L)

The effects of piperonyl butoxide (PBO) and beta-naphthoflavone (BNF) on cytochrome P4501A (CYP1A) expression and activity in juvenile Atlan tic salmon (Sabo salar L.) with regard to time and temperature was inv estigated. The time exposure study was performed at 8 degrees C, and t he results show that PBO, although acutely functioning as a CYP1A inhi bitor, is able to induce CYP1A expression in salmon liver. Both PBO an d BNF give highest induction of CYP1A mRNA 48 h after intraperitoneal injection (five- and 14-fold, respectively). The mRNA levels induced b y PBO and BNF were sustained during the 8 d of the experiment (four- a nd 11-fold, respectively). The CYP1A protein content measured by enzym e-linked immunosorbent assay demonstrated the highest induction by PBO 8 d after exposure (eightfold) and by BNF 4 d after exposure (11-fold ). Activity of CYP1A measured by ethoxyresorufin-O-deethylase (EROD) d emonstrated inhibition after PBO treatment the first 24 h after exposu re, followed by threefold induction from 48 h and to the end of the ex periment (8 d). beta-Naphthoflavone strongly induced EROD activity, wi th the highest levels occurring 4 d after treatment (56-fold) and 8 d after treatment (22-fold). In the temperature study, the results demon strated temperature compensation, as salmon acclimated to 7 degrees C for 3 weeks had a significantly higher EROD activity than those acclim ated to 11 and 15 degrees C. This was not reflected in significantly h igher levels of reduced nicotinamide adenine dinucleotide phosphate cy tochrome c reductase activity or CYP1A protein. The inductive properti es of PBO and BNF on CYP1A expression was also demonstrated in primary cultures of salmon hepatocytes.