Isotopic Tracer Studies on the Effect of Vitamin D on Calcium Metabolism in the Chick

THE relation of vitamin D to the metabolism of calcium has been a subject of continuing interest. In recent years availability of the radioactive isotope Ca45 has been an added incentive to explore this relationship. Rickets, the syndrome of vitamin D deficiency, is well understood from the standpoint of pathology. However, the mode of action of vitamin D has not been explained in biochemical terms. Several investigators (Nicolaysen, 1937a, b; Greenberg, 1945; Migicovsky and Emslie, 1949, 1950; Migicovsky and Nielsen, 1951; Migicovsky and Jamieson, 1955) have emphasized the effect of vitamin D on absorption of calcium. Other primary and secondary effects suggested for vitamin D have included a direct effect on mineralization of bone, decreased dissolution of bone salts and decreased excretion of calcium into the lower gut. In this paper the results of administering Ca45 orally and by injection to chicks in varying states of vitamin D nutrition are described.