Comparative Physiology of the Thyroid Hormone

Abstract

This review reveals that a functional thyroid tissue is found in all classes of vertebrates. In ammocetes larvae I is stored in certain cells of the endostylar tissue as shown by radioactive tracers. I is likewise stored very early in the thyroids of tadpole-like larvae of several animals. In rats, tracer tests show that I is stored on the 18th or 19th day, and definite histologic features can be correlated with this storage. Generalizations may not be made for other mammals as to the initiation of such storage. Human thyroid from fetuses of the latter part of the 3d month, transplanted into tadpoles, induce metamorphosis. The relationship between metabolic and morphogenetic actions of the thyroid hormone are discussed, as are studies dealing with growth and metabolism during larval or fetal development.