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METHOXYCHLOR METABOLISM AND VITELLOGENINESIS IN MALE RAINBOW TROUT LIVER SLICES
Citation:
Sheedy, B R., M A. Tapper, M. W. Hornung, R C. Kolanczyk, AND P. K. Schmieder. METHOXYCHLOR METABOLISM AND VITELLOGENINESIS IN MALE RAINBOW TROUT LIVER SLICES. Presented at Society of Toxicology 40th Annual Meeting, San Francisco, CA, March 25-29, 2001.
Description:
Induction of vitellogenesis (VTG) in male fish has become an accepted biomarker for xenoestrogenicity. This study utilized the male rainbow trout liver slice model to determine the estrogenicity of parent compound, methoxychlor (MXC) and metabolites, di-hydroxy methoxychlor (HPTE) and mono-hydroxy methoxychlor (MHMXC). Tissue slices were exposed to concentrations of MXC, HPTE or MHMXV for 72 h at ll oC. VTG induction was assessed by measurement of VTG mRNA (Northern dot blot and RPA analysis) and VTG protein in slices exposed to estradiol (E2; 0.1 - 1,000 nM) were a positive control. There was significant induction at 72 h of both VTG mRNA and VTG protein in slices exposed to 10,000 nM MXC or 10,000 nM HPTE. Exposure of slices to MHMXC resulted in no detectable induction of VTG mRNA or protein at the concentrations tested. Chemical concentrations were measured in the exposure media at 0 and 72 h. HPTE or MHMXC were undetectable after 72 h, presumably due to rapid Phase II metabolic conjugation as seen with disappearance of E2 observed previously in trout liver slices. While MXC concentrations decreased from initial exposure levels, detectable MXC was measured at 72 H. Thus, the rate of MXC metabolism in liver slices was significantly less than observed for E2, although adequate to support VTG reporter gene assay (RTH-149 cells 18 o C) where apparent lack of metabolic conversion of MXC to hydroxylated metabolites resulted in duction only upon exposure of cells to HPTE, but not MXC. The ability of the liver slices to metabolize MXC, presumably to HPTE prior to conjugation, is consisent with VTG induction noted in slices but not in the RTH-149 reporter gene assay where metabolism was absent. This demonstrates the utility of using a metabolically competent assay system to detect VTG induction as a consequence of biotransformation for screening of chemicals for potential endocrine disruption.