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ToxSci Advance Access originally published online on May 18, 2005
Toxicological Sciences 2005 86(2):273-280; doi:10.1093/toxsci/kfi203
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© The Author 2005. Published by Oxford University Press on behalf of the Society of Toxicology. All rights reserved. For Permissions, please email: journals.permissions@oupjournals.org

Effects of Atrazine on CYP19 Gene Expression and Aromatase Activity in Testes and on Plasma Sex Steroid Concentrations of Male African Clawed Frogs (Xenopus laevis)

Markus Hecker*,1, June-Woo Park*, Margaret B. Murphy*, Paul D. Jones*, Keith R. Solomon{dagger}, Glen Van Der Kraak{ddagger}, James A. Carr§,¶, Ernest E. Smith, Louis du Preez||, Ronald J. Kendall and John P. Giesy*,|||

* Department of Zoology, National Food Safety & Toxicology Center, Center for Integrative Toxicology, Michigan State University, East Lansing, Michigan 48824; {dagger} Centre for Toxicology and Department of Environmental Biology, University of Guelph, Guelph, Ontario, N1G 2W1, Canada; {ddagger} Department of Integrative Biology, University of Guelph, Ontario, NIG 2W1, Canada; § Department of Biological Sciences, Texas Tech University, Lubbock, Texas 79409; Department of Environmental Toxicology, and The Institute of Environmental & Human Health, Texas Tech University, Lubbock, Texas 79416; || North West University for Christian Higher Education, Potchefstroom 2520, South Africa; ||| Department of Biology and Chemistry, City University of Hong Kong, Kowloon, Hong Kong, SAR, China

Received February 23, 2005; accepted May 9, 2005

Some investigators have suggested that the triazine herbicide atrazine can cause demasculinization of male amphibians via upregulation of the enzyme aromatase. Male adult African clawed frogs (Xenopus laevis) were exposed to three nominal concentrations of atrazine (1, 25, or 250µg atrazine/l) for 36 days, and testicular aromatase activity and CYP19 gene expression, as well as concentrations of the plasma sex steroids testosterone (T) and 17ß-estradiol (E2), and gonad size (GSI) were measured. There were no effects on any of the parameters measured, with the exception of plasma T concentrations. Plasma T concentrations in X. laevis exposed to the greatest concentration of atrazine were significantly less (p = 0.034) than those in untreated frogs. Both CYP19 gene expression and aromatase activities were low regardless of treatment, and neither parameter correlated with the other. We conclude that aromatase enzyme activity and gene expression were at basal levels in X. laevis from all treatments, and that the tested concentrations of atrazine did not interfere with steroidogenesis through an aromatase-mediated mechanism of action.

Key Words: estrogen synthesis; gene expression; amphibians; endocrine modulation; Q-RT-PCR; aromatase.


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W. Kloas, I. Lutz, T. Springer, H. Krueger, J. Wolf, L. Holden, and A. Hosmer
Does Atrazine Influence Larval Development and Sexual Differentiation in Xenopus laevis?
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