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Description and initial evaluation of a Xenopus metamorphosis assay for detection of thyroid system‐disrupting activities of environmental compounds
Author(s) -
Opitz Robert,
Braunbeck Thomas,
Bogi Christian,
Pickford Daniel B.,
Nentwig Gerrit,
Oehlmann Jorg,
Tooi Osamu,
Lutz Ilka,
Kloas Werner
Publication year - 2005
Publication title -
environmental toxicology and chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.1
H-Index - 171
eISSN - 1552-8618
pISSN - 0730-7268
DOI - 10.1897/04-214r.1
Subject(s) - metamorphosis , xenopus , tadpole (physics) , propylthiouracil , thyroid , african clawed frog , biology , larva , medicine , amphibian , endocrinology , ecology , biochemistry , physics , particle physics , gene
A eedi recognizedforthedevelopmentandevaluationofbioassaysfordetectionofthyroid s stem–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 μg/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.