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ToxSci Advance Access published online on July 25, 2003
Toxicological Sciences, doi:10.1093/toxsci/kfg192
Toxicological Sciences © Society of Toxicology 2003; all rights reserved
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Received April 17, 2003; accepted June 30, 2003
© 2003 Society of Toxicology

Biotransformation and Toxicokinetics

Dieldrin Stimulates Biliary Excretion of [14C]Benzo[a]pyrene Polar Metabolites but Does Not Change the Biliary Metabolite Profile in Rainbow Trout (Oncorhyncus mykiss)

Melanie L. Barnhill 1, Marie V. M. Rosemond 1, and Lawrence R. Curtis 1*

1 Department of Environmental and Molecular Toxicology, Oregon State University, Corvallis, Oregon, 97331

* To whom correspondence should be addressed. E-mail: larry.curtis{at}orst.edu.


  Abstract

Activities of hepatic microsomal and cytosolic epoxide hydrolases, accumulation of dieldrin in liver, and in vivo metabolism and disposition of the polycyclic aromatic hydrocarbon (PAH), benzo[a]pyrene (BP), were examined in rainbow trout pretreated with dieldrin, a chlorinated cyclodiene insecticide. Rainbow trout were fed 0.3 mg dieldrin/kg/d for 9 weeks and the same dose of dieldrin for 9 weeks, followed by 3 weeks on control diet (12 weeks). Fish then received an intraperitoneal (ip) challenge dose of [14C]BP (10 µmol/kg). Dieldrin pretreatment significantly elevated the concentration of [14C]BP in bile (142% and 200% at 9 and 12 weeks, respectively), but not liver or fat. Extraction of bile sub-samples confirmed dieldrin pretreatment significantly stimulated total biliary excretion of [14C]BP polar metabolites (244% and 221% at week 9 and 12, respectively). The complex metabolism of BP characterized the in vivo state of the CYP system, UDP-glucuronyltransferases, and sulfotransferases. Bile was extracted and then hydrolyzed by {beta}-glucuronidase and arylsulfatase to regenerate BP metabolites conjugated by phase II enzymes. Evaluation of biliary polar metabolite profiles of [14C]BP revealed no significant differences between control and dieldrin-fed fish. There was no selective enhancement of any particular metabolite, or formation of a novel metabolite with dieldrin pretreatment. This research confirmed that enhanced biliary excretion, following chronic dieldrin exposure, was not explained by induction of xenobiotic metabolizing enzymes. The results are consistent with induction of hepatic intracellular trafficking proteins in dieldrin-fed fish.

Key Words: benzo[a]pyrene, biliary excretion, dieldrin, in vivo metabolism, rainbow trout .


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