Abstract
The parathyroid gland of Rana catesbiana in summer season was studied with electron microscope and compared to the frog parathyroid gland under artificial hibernation.
In the parathyroid gland of the summer frog the parenchyma was mostly composed of the large chief cells having numerous cell organelles and only a few small chief cells having poorly developed cell organelles were observed in the central region. In the parathyroid gland 2 to 5 weeks after artificial hibernation the number of the small chief cells was increased in the central region, the number of the large chief cells being decreased in the peripheral region of the gland. There were transitional forms between these two types of the chief cell. No remarkable changes were recognized in the ultrastructure of the small chief cells after artificial hibernation.
In the large chief cells of the parathyroid gland afer artificial hibernation, cell organelles such as granular endoplasmic reticulum and the Golgi apparatus became smaller in size than those of the control frogs. Small secretory granules, large secretory granules, homogeneously dense bodies with a low electron density, and vacuolar bodies containing floccular substance, dense material, vesicles and/or lipidlike substance were reduced in number after the experiment. There were transitional forms between each of secretory granules, homogeneously dense bodies and vacuolar bodies. It is conceivable that large secretory (storage) granules were changed into vacuolar bodies through homogeneously dense bodies.
Small secretory granules were seen near the plasma membrane, their limiting membrane was linked to the plasma membrane by a filamentous structure, and the contents of them communicated with intercellular space through a hiatus in the plasma membrane. These observations suggest that internal core of small secretory granule may be discharged through a hiatus in the plasma membrane into the extracellular space.
