Calcium Homeostasis in Chronic Thyrocalcitonin Deficiency

Abstract

Chronic thyrocalcitonin (TC) deficiency was produced in rats by thyroidectomy and thyroxine replacement. These and control animals had the parathyroids implanted into neck muscles. Four to 5 weeks after surgery, administration of Ca (0.15 mEq/100 g ip) produced marked and prolonged hypercalcemia in TC-deficient rats. Basal plasma Ca in these animals was the same as in the controls. Parathy-roidectomy made no difference to the Ca tolerance pattern in TC-deficient and control animals. When 45Ca tracer was given to the 2 groups of rats either with or 8 days before the Ca load, changes in the plasma 45Ca activity (absolute and specific) indicated that TC acts by inhibiting bone resorption. Inhibition of bone resorption by TC during hypercalcemia is an important hemeostatic process which is permanently impaired in thyroidectomized animals. The growth and general health of rats seemed unaffected by TC deficiency.