W3 PM Biomarkers
Wednesday, 16 November 2005: 1:50 PM - 5:30 PM in Ballroom 3

(AAA-1117-746010) Biomarkers of thyroid dysfunction in amphibians.

Hu, F¹, Sharma, B², Patino, R³, Carr, J¹, ¹ Texas Tech U, Lubbock, TX, USA² Texas Cooperative Fish & Wildlife Research Unit, Texas Tech U, Lubbock, TX, USA³ 3. USGS Texas Cooperative Fisheries and Wildlife Research Unit, Texas Tech U, Lubbock, TX, USA

ABSTRACT- Global declines in amphibian populations are of increasing concern. Factors responsible for these declines may include environmental contaminants, some of which can act as endocrine disruptors. Thyroid hormones are essential for amphibian development; thus, contaminants that impair thyroid physiology or action may adversely affect amphibian health. However, the degree to which sublethal exposures to contaminants contribute to amphibian population declines is at present uncertain. The goal of this research is to develop biomarkers of thyroid dysfunction for application to field studies of amphibian health. Evaluation of thyroid toxicity focused on a new marker developed for zebrafish: immunocytochemistry-based thyroid hormone ring depletion. Depletion of the thyroid hormone ring, found at the interphase of the epithelium and colloid in fish thyroid follicles, was much more sensitive in zebrafish follicles than standard markers of thyroid toxicity such as epithelial hypertrophy. In this study, thyroid dysfunction was experimentally induced in larvae of Xenopus laevis by exposure to perchlorate. Perchlorate is a widespread military waste product known to interfere with thyroid hormone synthesis and to impair amphibian metamorphosis. Xenopus larvae were exposed to 0, 1, 10, 100 and 1000 ppb (nominal) sodium perchlorate beginning at Nieuwkoop-Faber-stages 1-10 (< 24 h after fertilization) for a total of 68 days post-hatch. Animals were collected as they completed metamorphosis (Stage 66) in all treatments. Morphological standards of metamorphosis such as cumulative percent completing metamorphosis, cumulative percent forelimb emergence, and hindlimb growth were significantly decreased by perchlorate at 100 and 1000 ppb. Preliminary observations confirmed the presence of the thyroid hormone ring in Xenopus thyroid follicles. Quantitative measurements of epithelial hypertrophy, colloid depletion, and thyroid hormone ring depletion are currently in progress. Results from this study will assist in the development and validation of biomarkers of thyroid toxicity in amphibians for their application to field studies of amphibian health. This study was funded by a grant from the USGS Amphibian Research and Monitoring Initiative (ARMI) program.

Key words: Endocrine disruption, Amphibians, Thyroid, Biomarker