ToxSci Advance Access originally published online on September 18, 2009
Toxicological Sciences 2009 112(2):344-353; doi:10.1093/toxsci/kfp227
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Published by Oxford University Press 2009.
Dynamic Nature of Alterations in the Endocrine System of Fathead Minnows Exposed to the Fungicide Prochloraz
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* Mid-Continent Ecology Division, National Health and Environmental Effects Research Laboratory, Office of Research and Development, U.S. Environmental Protection Agency, Duluth, Minnesota 55804
Ecological Exposure Research Division, National Exposure Research Laboratory, Office of Research and Development, U.S. Environmental Protection Agency, Cincinnati, Ohio 45268
1 To whom correspondence should be addressed. Fax: (218) 529-5003. E-mail: ankley.gerald{at}epa.gov.
Received September 2, 2009; accepted September 9, 2009
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Abstract |
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The vertebrate hypothalamic-pituitary-gonadal (HPG) axis is controlled through various feedback mechanisms that maintain a dynamic homeostasis in the face of changing environmental conditions, including exposure to chemicals. We assessed the effects of prochloraz on HPG axis function in adult fathead minnows (Pimephales promelas) at multiple sampling times during 8-day exposure and 8-day depuration/recovery phases. Consistent with one mechanism of action of prochloraz, inhibition of cytochrome P450 (CYP) 19 aromatase activity, the fungicide depressed ex vivo ovarian production and plasma concentrations of 17β-estradiol (E2) in female fish. At a prochloraz water concentration of 30 µg/l, inhibitory effects on E2 production were transitory and did not persist during the 8-day exposure phase. At 300 µg/l prochloraz, inhibition of E2 production was evident throughout the 8-day exposure but steroid titers recovered within 1 day of cessation of exposure. Compensation or recovery of steroid production in prochloraz-exposed females was accompanied by upregulation of several ovarian genes associated with steroidogenesis, including cyp19a1a, cyp17 (hydroxylase/lyase), cyp11a (cholesterol side-chain cleavage), and follicle-stimulating hormone receptor. In male fathead minnows, the 8-day prochloraz exposure decreased testosterone (T) production, possibly through inhibition of CYP17. However, as for E2 in females, ex vivo testicular production and plasma concentrations of T recovered within 1 day of stopping exposure. Steroidogenic genes upregulated in testis included cyp17 and cyp11a. These studies demonstrate the adaptability of the HPG axis to chemical stress and highlight the need to consider the dynamic nature of the system when developing approaches to assess potential risks of endocrine-active chemicals.
Key Words: fish; prochloraz; endocrine function; compensation; recovery.