Parathyroid morphology in rats after administration of active vitamin D3

The morphology of the parathyroid gland was examined in rats treated for one month with an active vitamin D3, 1 alpha-hydroxyvitamin D3. On continuous administration of 12.5 micrograms/kg/day of 1 alpha-hydroxyvitamin D3, the first histological change of the parathyroid gland, seen on day 10, was atrophy of the chief cells with marked accumulation of prosecretory granules. Replacement of the parenchyma by small or large cysts was evident on days 20 and 30. The remaining portion of the parathyroid parenchyma showed various histological changes: widened intercellular spaces intermingled with many cytoplasmic processes, shrinkage of the cytoplasm of the chief cells, and the presence of a few ghost cells in cysts. The appearance of cysts may be caused by suppression of parathyroid hormone secretion and is a characteristic lesion in hypervitaminosis in rats induced by treatment with active vitamin D3.