Thyrocalcitonin Content of Thyroid Glands from Cows with Vitamin D-Induced Hypercalcemia1

Pharmacologic doses of vitamin D administered to adult cows for 3, 5, 7, 10, 14 and 30 days resulted in a marked reduction in the thyrocalcitonin (TCT) content of the thyroid glands. The depletion of TCT was considered to be a result of the persistent hypercalcemia that developed initially on the 3rd day of vitamin D administration. The TCT content of the thyroids from cows receiving vitamin D for 5 days was only 4 % of control cows. However, cows receiving vitamin D for 5 days followed by a 48 hr interval with no vitamin D accumulated TCT in the thyroid gland to within the range of control cows. The release of TCT and subsequent hypertrophy and hyperplasia of parafollicular cells did not prevent the development of hypercalcemia due to vitamin D administration. (Endocrinology86: 1463, 1970)