Correlation among the changes in the levels of thyroid hormones, thyrotropin and thyrotropin-releasing hormone during the development of Xenopus laevis.

The influence of thyroid hormones on neurogenesis suggested that these hormones might affect the maturation and development of neural centers which ultimately regulate thyroid function. Changes in the levels of the thyroid hormones, thyrotropin and the thyrotropin-releasing hormone in 'brain' and 'thyroid' fractions were, therefore, correlated at several developmental stages. All hormones showed increases from their initial detection through metamorphosis. The thyroid hormones were observed earliest in both fractions. These data are consistent with the notion that thyroid hormones influence the maturation of the particular neural regions whose later function is the regulation of the hypophyseal-thyroid axis.