RADIOAUTOGRAPHTC STUDIES ON THE ULTIMOBRANCHIAL BODY AND THYROID GLAND IN VERTEBRATES: FISHES AND AMPHIBIANS1

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Abstract
The possibility that the ultimobranchial bodies of lower vertebrates may share with the thyroid gland the ability to metabolize iodine has been investigated through use of radioactive iodine and radioautography. Carrier-free I131 was administered to selected teleosts (Ameiurus melas, Carassius auratus, and Cyprinus carpio) and amphibians (Ambystoma maculatum, A. tigrinum, Bufo americanus, Desmognathus quadramaculatus, D. monticola, Rana pipiens, Taricha torosus, Triturus v. viridescens, and Xenopus laevis). Radioautographs of ultimobranchial glands prepared from both normal and experimental (thyroidectomized and hypophysectomized) specimens disclose no storage of iodine by their follicles under conditions which (in normal individuals) gave high accumulations in the thyroid gland. The ultimobranchial bodies of juvenile and adult salamanders (D. quadramaculatus, D. monticola, Taricha torosus, and Triturus v. viridescens) do not hypertrophy after thyroidectomy. In both Bufo and Rana larvae similar responses of the ultimobranchial bodies to hypophysectomy were observed. There is marked retardation of development and differentiation of the gland and the single follicle, typical of normal larvae, is permanently retained. The ultimobranchial bodies of lower vertebrates never come in direct contact with the thyroid gland, nor do they serve as accessory thyroid tissues. Furthermore, inconstancy of secretory activity coupled with considerable variation in size and morphology of the ultimobranchial glands suggest that they are not of any endocrine importance.