An Inhibitory Effect of Thyrocalcitonin on Calcium Releasein Vivoand on Bone Metabolismin Vitro1

The effect of acute injection of a crude preparation of thyrocalcitonin on the stable and radioactive calcium of serum was studied at different times after the administration of 45Ca to rats. Thyrocalcitonin produced no change from controls in serum 45Ca when given to rats labeled with the isotope 3 hr previously but caused a significant reduction in 40Ca. When 45Ca had been given 2 weeks prior to thyrocalcitonin, however, both the serum 40Ca and 45Ca were significantly reduced. Under similar conditions parathyroid extract caused an increase in both isotopes of calcium in the serum, but no changes from control were produced when both parathyroid extract and thyrocalcitonin were given concomitantly. Calvaria from animals injected with thyrocalcitonin incubated in vitro had a lower glucose uptake and lactate production and a reduced specific activity of matrix hydroxyproline and hexosamine when compared with controls. These observations seem most compatible with the hypothesis that thyrocalcitonin causes an inhibition of the metabolically active bone resorption. (Endocrinology78:1139,1966)