| Summary: | In this study, we used reporter gene assays in COS-1 cells to examine the activation of rat pregnane X receptor (PXR), rat constitutive androstane receptor (CAR) and rat peroxisome-proliferator activated receptor (PPAR)α by pyrethroid pesticides, and to understand the effects of metabolic modification on their activities. All eight pyrethroids tested in this study showed rat PXR agonistic activity; deltamethrin was the most potent, followed by cis-permethrin and cypermethrin. However, when the pyrethroids were incubated with rat liver microsomes, their rat PXR activities were decreased to various extents. Cis- and trans-permethrin showed weak rat CAR agonistic activity, while the other pyrethroids were inactive. However, fenvalerate showed dose-dependent inverse agonistic activity toward rat CAR, and this activity was reduced after metabolism. None of the pyrethroids showed rat PPARα agonistic activity, but a metabolite of cis-/trans-permethrin and phenothrin, 3-phenoxybenzoic acid, activated rat PPARα. Since PXR, CAR and PPARα regulate various xenobiotic/endobiotic-metabolizing enzymes, activation of these receptors by pyrethroids may result in endocrine disruption due to changes of hormone-metabolizing activities.
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