Self-reproducing populations of lake trout have not yet become reestablished in the Great Lakes following their marked decline in the 1960s, despite years of ambitious stocking. Recent evidence in both mammals and fish indicates that some xenoestrogens may act by inhibiting the metabolism of endogenous estradiol-17beta (E2). The present study was conducted to elucidate the biochemical pathways of B2 metabolism in the lake-trout kidney and liver, and test the hypothesis that specific xenobiotics inhibit E2 metabolism in these tissues. The effects of key endogenous steroids hormones on E2 metabolism were also evaluated, E2 metabolites were quantified and positively identified by LC/MS. E2 metabolism was quantified by incubating primary kidney and liver tissue in vitro in the presence of radiolabelled E2 with or without added inhibitors. The major metabolite produced by both tissues was an unidentified hydroxylated estrogen metabolite(E2-0H) that was not estriol (E2-16-OH); the liver produced two- fold more E2-OH than the kidney. Other major products of both tissues were estradiol-17-glucuronide (E2-17-G), estradiol-17-sulfate (E2-17-S), and estradiol-3-glucuronide (E2-3-G); the kidney produced two-fold more conjugated metabolites than the liver. E2 metabolism was inhibited in both kidney and liver by the following compounds at a dose of 300 uM: 4,4'-(OH)2-3,3',5,5'-tetrachlorobiphenyl (4,4'- OH-TCB), bisphenol A (BPA), tetrabromobisphenol A (TB- BPA), tetrachlorobisphenol A (TC-BPA), tribromophenol (TBP); trichlorophenol (TCP), and pentachloropheno] (PCP), The alkylphenols, 4-n-nonylphenol (NP) and 4-octylphenol (OP), and 2,2'4,4'-tetrabromodiphenyl ether (TBDE), had little or no effect on E2 metabolism by either tissue. Testosterone (T), 11-ketotestosterone (ll-KT), 17alpha,20beta-dihydroxy-4-pregnen-3-one (17,20P), and cortisol all inhibited E2 metabolism in the kidney. Only T and 17,20P inhibited E2 metabolism in the liver. IC50 values were determined for 4,4'-OH-TCB and BPA as follows: 4,4'-OH- TCB, kidney, 32, 28, and 7 uM; 4,4'-OH-TCB, liver, 1.6; 1.5, and 0.6 uM; BPA, kidney, 94, 108, and 40 uM; and BPA, liver, 11, 18, and 11 uM. Low doses (0.1 uM) of 4,4'-OH-TCB and BPA significantly increased estrogen metabolism in the kidney. These results indicate that the inhibition of E2 conjugation may be an important mechanism mediating the effects of xenoestrogens in lake trout.
