title: Description and initial evaluation of a Xenopus metamorphosis assay for detection of thyroid system-disrupting activities of environmental compounds.
abstract: A need is recognized for the development and evaluation of bioassays for detection of thyroid system-disrupting compounds. The issue of testing for thyroid disruption can be addressed by exploiting amphibian metamorphosis as a biological model. In the present study, a test protocol for a Xenopus metamorphosis assay (XEMA) was developed and its interlaboratory transferability was evaluated in an informal ring test with six laboratories participating. In the XEMA test, exposure of Xenopus laevis tadpoles was initiated at stages 48 to 50 and continued for 28 d. Development and growth of tadpoles were assessed by means of developmental stage and whole body length determinations, respectively. For initial test protocol evaluation, thyroxine (T4), and propylthiouracil (PTU) were used as positive controls for thyroid system-modulating activity, and ethylenethiourea (ETU) was used as a test compound. Exposure of tadpoles to 1 microg/L T4 produced a significant acceleration of metamorphosis whereas PTU concentrations of 75 and 100 mg/L completely inhibited metamorphosis. Five different ETU concentrations (5, 10, 25, 50, and 100 mg/L) were tested and a concentration-dependent inhibition of metamorphosis was observed. None of the compounds affected tadpole survival, and only PTU caused a slight retardation in tadpole growth. This study demonstrates that the XEMA test provides a sensitive, robust, and practical testing approach for detection of compounds with both agonistic and antagonistic effects on the thyroid system in Xenopus tadpoles.
authors.affiliation: Department of Inland Fisheries, Leibniz-Institute of Freshwater Ecology and Inland Fisheries, Berlin D-12587, Germany.
authors.forename: Robert
authors.initials: R
authors.lastname: Opitz
authors.forename: Thomas
authors.initials: T
authors.lastname: Braunbeck
authors.forename: Christian
authors.initials: C
authors.lastname: Bögi
authors.forename: Daniel B
authors.initials: DB
authors.lastname: Pickford
authors.forename: Gerrit
authors.initials: G
authors.lastname: Nentwig
authors.forename: Jörg
authors.initials: J
authors.lastname: Oehlmann
authors.forename: Osamu
authors.initials: O
authors.lastname: Tooi
authors.forename: Ilka
authors.initials: I
authors.lastname: Lutz
authors.forename: Werner
authors.initials: W
authors.lastname: Kloas
mesh_terms: D000818:Animals; D001681:Biological Assay / Q000379:methods*; D049628:Body Size / Q000187:drug effects; D004785:Environmental Pollutants / Q000633:toxicity; D005031:Ethylenethiourea / Q000633:toxicity*; D007814:Larva / Q000187:drug effects / Q000254:growth & development / Q000378:metabolism; D008675:Metamorphosis, Biological / Q000187:drug effects*; D011441:Propylthiouracil; D013961:Thyroid Gland; D013974:Thyroxine; D014982:Xenopus laevis / Q000254:growth & development* / Q000378:metabolism
chemical_list: D004785:Environmental Pollutants; D005031:Ethylenethiourea; D011441:Propylthiouracil; D013974:Thyroxine