The response of thyroid C-cell system in rat to long-term hypercalcemia.

Long-term hypercalcemia induced in rats by administration of vitamine D3 and CaCl2 for 60 days resulted in strong hyperplasia and hypertrophy of C-cells. The extent of hyperplasia varied greatly in individual animals. Histochemical reactions, especially the masked metachromasy with toluidine blue, demonstrated cell groups in which no reaction was observed beside those exhibiting a very strong reaction. Impregnation with silver according to Cajal showed a diminished number of argyrophilic granules in the C-cells, which had undergone hyperplasia. The reactions for non-specific esterases and cholinesterases were similar both in the experimental animals and in the controls. An enlargement of the C-cell nuclei in the experimental group was also pronounced. The total serum calcium level was only slightly increased in this group. It is concluded that the results of staining and the enlargement in nuclear volume of C-cells reflect the increased activity of these cells. Hyperplasia of the C-cells may represent a type of adaptation of the endocrine system in order to maintain calcium homeostasis.