Abstract
Electron microscopic studies were made on the parafollicular cells of the thyroids of normal, vitamin D plus CaCl2-injected, and CaCl2-injected mice.
1. The cytoplasmic granules of 200mμ diameter are reduced in number in the animals treated with vitamin D plus CaCl2 everyday for 2 or 7 days. In these animals the Golgi field is enlarged containing numerous small vesicles and newly formed small granules, suggesting an active granule formation there.
2. No marked changes were observed in the parafollicular cells of the animals given CaCl2 everyday for 15 or 75 days.
3. The parafollicular cells remarkably reacting to the long-term hypercalcemia seem to be related to thyrocalcitonin production. Their granules are thought to be formed in the rough endoplasmic reticulum and Golgi apparatus system as in other protein secreting cells.
