198 L. LuTWAK 



diminution paradoxale de Caf en meme temps que le coefficient o. diminue; ceci fait 

 penser que, dans ces cas, la variation de concentration calcique provoquee par la chute 

 importante de la calcemie peut diminuer I'elimination de calcium par voie digestive. 



Bibliographic 



AuBERT, J. -P., et G. Milhaud: Mcthode de mesure du metabolisme calcique chez rhomme. 



Biochim. biophys. Acta 39, 22 (1960). 

 Bronner, F.: Dynamics and function of calcium. In Mineral Metabolism. Comar, C. L,, 



and F. Bronner (eds.). New York: Academic Press 1964, p. 341. 

 Heaney, R. p., and T. Skillman: Secretion and excretion of calcium by the human gastro- 

 intestinal tract. J. Lab. clin. Med. 64, 29 (1964). 

 Hioco, D., L. MiRAVET, and P. Bordier: Physiopathology and treatment of osteoporosis in 



younger men. In Bone and Tooth. Blackwood, H.J.J, (ed.). Oxford: Pergamon Press 



1964, p. 365. 

 Milhaud, G., J. -P. Aubert et J. Bourrichon: Etude du metabolisme du calcium chez 



I'homme a I'aide du Ca''"'. I: Absorption du calcium au cours de la digestion. Path, et 



Biol. 9, 1761 (1961). 



Absorption of Calcium in Man: Effect of Disease, 

 Hormones and Vitamin D "' 



L. LuTWAK 



Clinical Nutrition Unit, Graduate School of Nutrition, Cornell University, Sage Hospital, 

 512 East State Street, Ithaca, N. Y., U.S.A. 



The kinetics of the absorption and retention of calcium were calculated from 

 measurements in vitro of isotope content of the forearm by counting in a large 

 volume liquid scintillation counter after the oral administration of '*^Ca (Lutwak 

 and Shapiro, 1964). The fecal excretion of unabsorbed tracer, and the urinary 

 excretion of absorbed isotope were also followed. These measurements permitted an 

 estimate of the rates of transfer of calcium from the gut to the arm during the initial 

 absorptive phase and the subsequent turnover of tracer calcium retained during the 

 first phase. 



After the oral administration of the tracer dose of ^"Ca of between four and eight 

 microcuries admixed with 100 mgm. of stable calcium, in the form of skim milk or 

 calcium gluconate, the radioactivity appearing in the patient's forearm counted in 

 vivo is followed at three minute intervals for the first five to six hours and thereafter 

 twice a day. Blood samples were obtained at 15 minute to half hour intervals over 

 the course of the first four hours to monitor the procedure. Maximum levels of blood 

 radioactivity are seen in most of our patients between two and four hours after the 

 ingestion of the tracer, and thereafter fall quite rapidly. Assuming a value for extra- 

 cellular fluid in the forearm of approximately 150 — 200 ml., between 20 and 40''/o 

 of the radioactivity appearing in the forearm in the first three of four hours can be 

 attributed to radioactivity in the blood, and remainder being that which has been 

 taken up by bone. 



* This paper was prepared with the support of grant number AM-07451 from the National Institutes of 

 Health. 



