Direct Regulation of Bone Resorption of Chick Embryonic Femur in Organ Culture by the Change of Calcium or Phosphate ion Concentration in the Medium

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Bone resorbing activity was determined in organ culture by following the change of biological half life of ⁴⁵Ca (T_1/2) incorporated into bone salts of chick embryonic femur. The elevation of calcium or phosphate ion in the medium brought about an increase of T_1/2, indicating that the bone resorption was inhibited. Conversely, the decrease of calcium or phosphate content in the medium resulted in the decrease of T_1/2. A change of the magnesium ion concentration in the medium had no discernible effect on T_1/2. These results suggest that a direct regulating system exists between bone resorption of chick embryonic femur and calcium or phosphate content in the medium and this phenomenon is specific for calcium or phosphate ion.