Effect of methidathion on the cytochrome P-450 1A in the cyprinid fish gudgeon (Gobio gobio)

Effect of methidathion (organophosphate) on the P-450 1A induction was assessed both by measurements of the induction of the EROD activity and of the immunodetection of the CYP1A protein in gudgeon. Fish were pre-treated with 5 mg kg(-1) of beta-naphthoflavone (BNF) and exposed to environmental concentrations of methidathion in laboratory. Methidathion proved to inhibit EROD induction in vivo and in vitro. In contrast, levels of immunoquantified CYP1A were found to be slightly higher in microsomes from fish exposed to 10-30 mu g l(-1) of methidathion than in control fish exposed to BNF alone. This suggests that the inhibition of the EROD activity by methidathion resulted from a catalytic inhibition without decrease of the CYP1A protein. (C) 1998 Elsevier Science B.V. All rights reserved.