Acquired resistance to Ah receptor agonists in a population of Atlantic killifish (Fundulus heteroclitus) inhabiting a marine superfund site: In vivoand in vitro studies on the inducibility of xenobiotic metabolizing enzymes

New Bedford Harbor (NBH), MA, is a federal Superfund site that is heavily c ontaminated with polychlorinated biphenyls (PCBs) and other halogenated aro matic hydrocarbons (HAHs), including some potent aryl hydrocarbon receptor (AhR) agonists. A population of Atlantic killifish (Fundulus heteroclitus) continues to inhabit this site, despite accumulating extraordinarily high c oncentrations of PCBs (272 mug/g dry weight). To determine if NBH killifish have developed resistance to HAHs that act through the AhR, we examined th e inducibility of cytochrome P4501A1 (CYP1A1), UDP glucuronosyl transferase (UGT), and glutathione S-transferase (GST) in fish from NBH and a referenc e site, Scorton Creek (SC, Cape God, MA; PCB concentrations 0.177 mug/g dry weight). 2,3,7,8-Tetrachlorodibenzofuran (TCDF) induced CYP1A1 mRNA, prote in, and activity in SC fish in all tissues examined (liver, heart, gut, gil l, kidney, spleen, and gonad). In contrast, NBH fish expressed low levels o f CYP1A1 and showed no induction of CYP1A1 mRNA, protein, or activity by TC DF, or induction that was lower in magnitude or required higher doses of in ducer. p-Nitrophenol UGT activity was not induced by TCDF in either populat ion, while GST activity with 1-chloro-2,4-dinitrobenzene as substrate was i nduced only in NBH fish in one experiment. Inducibility of CYP1A1 by 2,3,7, 8-tetrachlorodibenzo-p-dioxin (TCDD) or beta -naphthoflavone (BNF) was meas ured in primary hepatocyte cultures prepared from SC and NBH fish. TCDD ind uced CYP1A1 activity (ethoxyresorufin O-deethylase) to the same degree in h epatocytes from both populations, demonstrating the functionality of the Ah R signaling pathway in NBH fish. However, hepatocytes from NBH fish were 14 -fold less sensitive to TCDD than were those from SC fish. The nonhalogenat ed AhR agonist BNF also induced CYP1A1 in cells from both populations, alth ough with only a 3-fold difference in sensitivity (NBH < SC). These results indicate that chronic exposure to high levels of HAHs has led to a reducti on in the sensitivity of NBH killifish to AhR agonists. The resistance is s ystemic and pretranslational, and exhibits compound-specific differences in magnitude. These findings suggest an alteration in the AhR signal transduc tion pathway in NBH fish.