The occurrence of chronic hypocalcemia following parathyroidectomy in the green frog, Rana clamitans

Amphibian parathyroids: morphological and functional aspects

Amphibians living partially or totally in a terrestrial environment are the first tetrapods to possess parathyroid glands. Purely aquatic amphibians and amphibian larvae lack these endocrine glands. The parathyroids develop at the time of metamorphosis. The parathyroid glands in caecilians consist of a single cell type, that of urodeles may be composed of basal (supporting) cells and suprabasal (chief) cells, and that of anurans of small and large chief cells. Parathyroid glands of caecilians and anurans lack connective tissue, blood vessels, and nerves. The parathyroid cells become activated in response to decreased blood calcium concentration and undergo changes indicating increased parathyroid hormone secretion. Increased blood calcium concentration suppresses secretory activity. Usually, parathyroidectomy elicits hypocalcemia in most amphibians. Such operations have no effect in lower urodeles. Parathyroid hormone administration provokes hypercalcemia in most amphibians. The parathyroids of caecilians have not been studied in detail. The urodeles and anurans exhibit seasonal changes in the parathyroid glands. These changes may be initiated by environmental stimuli such as light, temperature, or alterations in blood calcium levels caused by natural hibernation.

Evaluation of a radioimmunoassay for the measurement of amphibian parathyroid hormone

A commercial mid-region to carboxyl-region parathyroid hormone (PTH) radioimmunoassay (RIA) for measurement of PTH concentration in serum of humans was evaluated for its ability to detect amphibian PTH. The recovery of known amounts of human PTH added to aliquots of pooled frog serum demonstrated that frog serum does not interfere with the RIA system. The mean intraassay coefficient of variation was 0.11. During the spring and summer removal of the parathyroid glands from frogs resulted in significant decreases in serum calcium levels which the RIA revealed were associated with significant decreases in PTH levels. In the winter the parathyroid glands of frogs showed histological changes associated with inactivity. Also, parathyroidectomy of winter frogs did not affect serum calcium concentrations, and PTH levels of experimental and control animals were below or near the level of detection.