Abstract
The parathyroid gland of R ana rugosa under stimulated circumstances (administration of EDTA) was studied with electron microscope. The large chief cell in the peripheral region and the s m all chief cell in the central region of the parathyroid gland were distinguishable. The former was active and the latter was inactive in function. It was difficult to identify the light and dark chief cells. Remarkable changes in the fine structure of the small chief cell were not observed in the EDTA treated frogs. The principal variations of the experimental frogs were the increase in the number of cell organelles and of secretory granules (though granules decreased temporally in number) in most large chief cells, and the appearance of dense materials in the enlarged intercellular spaces. The number of secretory granules decreased at 0.5 hrs after administration of EDTA (serum calcium concentration was very low), and thereafter increased. It could be suggested that the secretory function of the parathyroid gland was accelerated from depressed serum calcium levels and temporary release of many secretory granules was induced in order to keep serum calcium at control level. Secretory granules were observed in the peripheral cytoplasm and dense materials thought to be derived from the contents of secretory granules were seen in the enlarged intercellular spaces. These observations suggest that secretory granules may be released by eruptocrine type of secretion. Most of the large chief cells at 0.5,1 and 2 h r s after administration of EDTA were observed in active stage of secretory cycle as compared with the control frogs.
