Iodine deficiency produces hypercalcemia and hypercalcitonemia in rats

To determine the effect of thyroid-stimulating hormone (TSH) on secretion of calcitonin by the thyroid, 50 male Sprague-Dawley rats were randomly separated into seven groups. The groups received different diets, medications, or operations [propylthiouracil (PTU), iodine-deficient diet, (LID), acute or chronic thyroxine treatment, sham operation (SO), hemithyroidectomy (Htx), and total thyroidectomy (Ttx)]. two weeks to six months later, serum TSH concentrations were increased in the Htx, Ttx, and LID groups when compared with SO animals. Serum calcitonin concentrations were increased in the LID- and PTU-treated groups and were decreased in animals that chronically received thyroxine. Serum calcium concentrations were increased in the LID animals, decreased in the Ttx animals, and were similar in the other groups. These findings suggest that TSH stimulates both follicular and parafollicular cells in the rat thyroid and that iodine deficiency causes hypercalcemia and hypercalcitonemia.