Endocrinology of amphibian ultimobranchial glands

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Abstract
The historical observations of the amphibian ultimobranchial gland are reviewed and interpreted in light of recent evidence which demonstrates the relationship of this organ to the hypocalcemic hormone, calcitonin. Its discrete anatomical location and separation from other endocrine tissues has made extirpation feasible and has revealed the importance of this gland in preventing excessive mobilization of calcium from the paravertebral lime sacs in larval and adult forms. These glands also appear to prevent hypercalcemia during periods of high dietary calcium ingestion. In view of its phylogenetic development and relationship to the parathyroids, two major functions of the ultimobranchial glands can be ascribed. First, amphibian calcitonin sequesters calcium in storage depots, in pre‐metamorphic and post‐metamorphic forms to insure maximal ossification of adult bone. Such protection in an aquatic environment deficient in calcium ions would be of extreme importance. Second, amphibian calcitonin prevents the rapid influx of calcium across gut epithelium during feeding to protect against acute periods of hypercalcemia. The diversity of aquatic and terrestrial amphibian types provides a broad spectrum of forms in which to develop model systems for calcium homeostasis.