The Regulation of Thyroid Stimulating Hormone Release from the Pituitary in Anuran Larvae
The EPA is developing a metamorphosis assay with African clawed frog (Xenopus laevis) tadpoles to screen for the ability of chemicals to disrupt elements of the hypothalamo-pituitary-thyroid (HPT) axis. However, a basic knowledge of the underlying endocrinology of the HPT axis in this species is necessary for predicting how the axis may respond to perturbation by chemicals. Included in this requisite knowledge is an understanding of the inherent compensatory mechanisms involved in maintaining thyroid hormone (TH) homeostasis. This research will examine compensatory mechanisms of the HPT axis of anuran larvae at the level of the pituitary by establishing the details of the regulation of thyroid stimulating hormone (TSH) release as a function of circulating TH levels. Specifically this research will determine the relative contributions of the pituitary and hypothalamus to initiating a compensatory response to changes in circulating TH concentrations. To determine if the pituitary acts alone or in concert with the hypothalamus in initiating a compensatory response to changes in circulating TH levels, intact gland or tissue (e.g., pituitary, hypothalamus) will be dissected from X. laevis larvae of different stages of TH-dependent metamorphosis and cultured in vitro, and the response of the cultured gland or tissue to various inputs will be measured. The results of this effort are expected to increase our basic understanding of the endocrinology of the HPT axis of anuran larvae. In addition, the results could be incorporated into an HPT systems model to serve as the framework for predicting the consequences of HPT perturbation by endocrine-disrupting chemicals on the whole organism.
Research project update date
June 22, 2011