ToxSci Advance Access published online on October 12, 2005
Toxicological Sciences, doi:10.1093/toxsci/kfj020
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1 National Research Council, Research Triangle Park, NC
* To whom correspondence should be addressed. The prevalence of pyrethroids in insecticide formulations has increased in the last decade. A common mode-of-action has been proposed for pyrethroids based on in vitro studies, which includes alterations in sodium channel dynamics in nervous system tissues, consequent disturbance of membrane polarization, and abnormal discharge in targeted neurons. The objective of this work was to characterize individual dose-response curves for in vivo motor function and calculate relative potencies for eleven commonly used pyrethroids. Acute oral dose-response functions were determined in adult male Long Evans rats for five Type I (bifenthrin, S-bioallethrin, permethrin, resmethrin, tefluthrin), five Type II ( Disclaimer: The information in this document has been funded wholly (or in part) by the U.S. Environmental Protection Agency. This manuscript has been reviewed following the policy of the National Health and Environmental Effects Research Laboratory, U.S. Environmental Protection Agency, and was approved for publication. Approval does not signify that the contents necessarily reflect the views and policies of the agency, nor does mention of trade names or commercial products constitute endorsement or recommendation for use.
Received July 18, 2005
Accepted October 7, 2005
Neurotoxicology
Relative Potencies for Acute Effects of Pyrethroids on Motor Function in Rats
2 Department of Biostatistics, Virginia Commonwealth University, Richmond, VA
3 Neurotoxicology Division, National Health and Environmental Effects Research Laboratory, Office of Research and Development, U.S. Environmental Protection Agency, Research Triangle Park, North Carolina
K. M. Crofton, E-mail: crofton.kevin{at}epa.gov
Abstract 
-cyfluthrin, 
-cyhalothrin, cypermethrin, deltamethrin, esfenvalerate) and one mixed Type I/II (fenpropathrin) pyrethroids [n=8-18 per dose; 6-11 dose levels per chemical, vehicle = corn oil, at 1 ml/kg]. Motor function was measured using figure-8 mazes. Animals were tested for one hour during the period of peak effects. All pyrethroids, regardless of structural class, produced dose-dependent decreases in motor activity. Relative potencies were calculated based on the computed ED30s. Deltamethrin, with an ED30 of 2.51 mg/kg, was chosen as the index chemical. Relative potency ratios ranged from 0.009 (resmethrin) to 2.092 (esfenvalerate). Additional work with environmentally-based mixtures is needed to test the hypothesis of dose-additivity of pyrethroids.
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