Skeletal calcium retention in hyperthyroidism and in vitro calcitonin inactivation

Studies on patients with severe hyperthyroidism revealed an increased skeletal avidity for calcium, expressed in terms of net retention, after a three-hour i.v. load of 10mg Ca/kg body weight. For the same hyperthyroid subjects the calcitonin inactivating potency of the sera was tested in vitro. The results were expressed as restant hypocalcemic potency of the calcitonin after incubation with the serum fractions. In hyperthyroid subjects two fractions in dilutions of 1:10 reduced the hypocalcemic activity of calcitonin by 75%. In normals this activity appeared only in one fraction. All these results suggest a prompt calcitonin release during calcium infusion which is however less efficient, probably because of the increased amount of calcitonin inactivating factor present in sera. The serum inactivating factor generally contributes to the short-time activity of calcitonin both in normals and in some clinical states with bone calcium imbalance.