Transient induction of 7-ethoxyresorufin-O-deethylase (EROD) activity by medium change in the rainbow trout liver cell line, RTL-W1

Cytochrome P4501A (CYP1A) metabolizes a wide array of lipophilic xenobiotic s. In fish liver, CYP1A is constitutively expressed at low levels, but xeno biotics can strongly induce CYP1A expression via a receptor-mediated pathwa y. While induction of hepatic CYP1A in teleosts by xenobiotics is well inve stigated, very little is known on the regulation of constitutive CYP1A expr ession and its induction by factors other than xenobiotics. In the present study we show that in the rainbow trout liver cell line, RTL-WI, CYP1A-cata lyzed 7-ethoxyresorufin-O-deethylase (EROD) activity can be induced by a ch ange of the culture medium, in the absence of xenobiotics. The increase in cellular EROD levels is of transient nature. Experiments with cell incubati on solutions supplemented with various medium components indicate that phot ooxidized tryptophan is the agent causing the increase of EROD activity aft er medium change. (C) 2000 Elsevier Science Ltd. All rights reserved.