Roles of Thyroxine and Thyrocalcitonin in the Response to Hypercalcemia in Rats1

Abstract

Chronically parathyroidectomized rats counteracted the hypercalcemia induced by intraperitoneal injection of Cft more rapidly than thyroparathyroidectomized rats, whether the rats compared were thyroxine-treated or not. The results indicate that the thyroid alone, in the absence of all parathyroid secretions, effects a Ca-lowering response in hypercalcemia in the rat, presumably by the release of thyrocalcitonin, a polypeptlde with demonstrated Ca-lowering activity. The thyroxine-dependent metabolic status of the animals also played a part in the rate of elimination of an exogenous hypercalcemia. The elimination was more rapid in thyroxine-treated than in saline-treated rats, whether normal thyroid tissue was present or not. Hence, evaluation of Ca tolerance after thyroidectomy requires consideration of the additive effects of lack of thyrocalcitonin and incipient classic hypothyroidism.