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Effects of hypoxia on the response of fish to estrogen exposure
Citation:
FLICK, R. W., J. M. LAZORCHAK, AND J. Oris. Effects of hypoxia on the response of fish to estrogen exposure . Presented at SETAC, Tampa, FL, November 16 - 20, 2008.
Impact/Purpose:
The indeterminate condition of exposure indicator research stands to change markedly with the ability to connect molecular biological technologies with cellular or tissue effects and outcomes. Three focal areas of ecological research aim to develop a sequence of approaches where "the earliest recognizable signatures of exposure" (i.e., unique patterns of up- and down-regulated genes and proteins) are identified for numerous stressors, demonstrable in case studies and incorporated into Agency, State and Regional studies supported by EMAP and other programs.
Description:
Natural and synthetic estrogens are common contaminants in surface waters and have the potential to affect reproduction in fish. Estrogens are likely to co-occur with low dissolved oxygen (DO) levels, which result from inputs of organic material in wastewater effluents or from animal production facilities. Low DO, or hypoxia, is a significant cause of impairment in streams and rivers. Their co-occurrence is particularly significant because the transcriptional responses to hypoxia and estrogen share a common element in their pathways. Therefore, the production of vitellogenin, which is often used as a biomarker of exposure to estrogens, may be affected by exposure to hypoxia. In order to determine if exposure to hypoxia altered the response of fish to estrogens, we performed laboratory exposures of fish to both hypoxia and 17a-ethynylestradiol (EE2) and used real-time PCR to analyze vitellogenin expression in liver tissue. In initial experiments fathead minnows were exposed to DO levels of approximately 2.5 mg/L for up to six hours; EE2 was then added to achieve a final concentration of 10 ng/L EE2, and exposure continued for 16 to 24 hours. Results from these experiments suggest that hypoxia does not substantially alter vitellogenin expression in short-term exposures to EE2 in fathead minnows compared to EE2-only exposed controls; however, larger sample sizes are necessary to verify these results. We will also investigate whether the transcriptional response is dependent upon duration of exposure and whether the expression of other genes, such as HIF-1a, is affected. In the future we hope to determine whether these responses are species-specific. Understanding the influence of non-chemical stressors on estrogenic responses in aquatic organisms is essential for accurate ecological assessment. If vitellogenin expression were found to be significantly altered by exposure to hypoxia, then its use as a biomarker to diagnose exposure to estrogens would require data on DO levels in order to accurately assess the level of exposure to estrogenic compounds.