Abstract
Hypercalcemia was induced in dogs by daily intramuscular injection of vitamine D3 300, 000 IU and administration of 0.5% CaCl2 in drinking water. After treatment for 10, 20 and 30 days, the serum calcium value rose respectively to 12.5, 22 and 18mg/dl from a normal level of 10mg/dl.
Light microscopic examination of the thyroids of these dogs revealed increased parafollicular cells with frequent mitotic figures. The number of mitotic parafollicular cells in serial sections of the thyroid increased in proportion to the duration of hypercalcemia. Dogs treated for 30 days showed mitotic figures 20-50 times more frequent than in the controls. In the most conspicuous case, 147 mitotic parafollicular cells occurred in a transverse section of the thyroid. The mitotic index reached 10% in this case.
The granules of the parafollicular cells stained by silver impregnation, pseudoisocyanin and lead-hematoxylin decreased in proportion to the duration of hypercalcemia. The parafollicular cells were almost completely degranulated after 30 days of treatment.
Degenerative changes such as pyknosis occurred in a part of the parafollicular cells, suggesting an exhaustion of the activated cells.
The parathyroid showed marked atrophic changes caused by induced hypercalcemia.
