title: Triclosan and thyroid-mediated metamorphosis in anurans: differentiating growth effects from thyroid-driven metamorphosis in Xenopus laevis.
abstract: In a previously reported study, we used a standard metamorphosis anuran model to assess potential effect of the antibacterial agent triclosan (TCS) on normal prometamorphic Xenopus laevis. Results indicated that environmentally relevant TCS concentrations did not alter the normal course of thyroid-mediated metamorphosis in this standard anuran model. However, to examine potential effects of TCS exposure during premetamorphosis and to distinguish between effects on metamorphosis and effects on growth, a longer term TCS exposure study was conducted. Standard Nieuwkoop and Faber (NF) stage 47 X. laevis larvae were exposed for 32 days (ca. NF stage 59-60) via flow-through to four different concentrations of TCS: < 0.2 (control), 0.8, 3.1, 12.5, or 50.0 μg TCS/l. Primary endpoints were survival, hind limb length, body length (whole; snout-to-vent), developmental stage, wet whole body weight, thyroid histology, plasma thyroid hormone (TH) concentrations, TH receptor beta (TRβ), and type II and III deiodinase (DI-2 and DI-3) expression. Endpoints measured to evaluate effects on thyroid-mediated metamorphosis including developmental stage, thyroid histology, TRβ expression, DI-2 and DI-3 expression, and thyroid gland 3,5,3',5'-tetraiodothyronine (T4) and plasma T4 and 3,5,3'-triiodothyronine (T3) levels were not affected by TCS exposure. However, increased larval growth based on whole body length (0.78, 12.5, and 50 μg TCS/l), snout-vent length (3.1 and 12.5 μg TCS/l), and whole body weight (0.8, 12.5, and 50.0 μg TCS/l) was observed following 32-day TCS exposure. These results indicated that TCS exposure during pre- and prometamorphosis increased larval growth but did not alter the normal course of metamorphosis in X. laevis. The increased growth associated with TCS exposure was not unexpected and is generally consistent with the presence of reduced bacterial stressors in culture.
authors: Fort Environmental Laboratories, Stillwater, Oklahoma 74074, USA. djfort@fortlabs.com
authors: Douglas J
authors: DJ
authors: Fort
authors: Michael B
authors: MB
authors: Mathis
authors: Warren
authors: W
authors: Hanson
authors: Chelsea E
authors: CE
authors: Fort
authors: Lisa T
authors: LT
authors: Navarro
authors: Robert
authors: R
authors: Peter
authors: Claudia
authors: C
authors: Büche
authors: Sabine
authors: S
authors: Unger
authors: Sascha
authors: S
authors: Pawlowski
authors: James R
authors: JR
authors: Plautz
mesh_terms: D000818:Animals; D018507:Gene Expression Regulation, Developmental; D007453:Iodide Peroxidase / Q000235:genetics / Q000378:metabolism; D007814:Larva / Q000187:drug effects / Q000254:growth & development; D008675:Metamorphosis, Biological / Q000187:drug effects*; D013961:Thyroid Gland / Q000187:drug effects / Q000254:growth & development* / Q000473:pathology; D037042:Thyroid Hormone Receptors beta / Q000235:genetics / Q000378:metabolism; D013974:Thyroxine / Q000097:blood; D014260:Triclosan / Q000009:adverse effects*; D014284:Triiodothyronine / Q000097:blood; D014982:Xenopus laevis / Q000254:growth & development* / Q000378:metabolism; D000097564:Iodothyronine Deiodinase Type II
chemical_list: D007453:Iodide Peroxidase; D037042:Thyroid Hormone Receptors beta; D013974:Thyroxine; D014260:Triclosan; D014284:Triiodothyronine; D000097564:Iodothyronine Deiodinase Type II; C117274:iodothyronine deiodinase type III