STRONTIUM AND CALCIUM METABOLISM IN METABOLIC BONE DISEASES *

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Abstract
The distribution and excretion of Sr85 and Ca45 administered simultaneously and intravenously was studied in patients with thyroid and parathyroid disorders, osteoporosis, and Paget''s disease. In all cases and at all times the body retention of Ca45 was more than Sr85 retention by a factor of 1.1 to 5.7. Differential renal clearance of the 2 isotopes accounted for 1.9 to 8.1 times more Sr85 than Ca45in the urine. The amounts of each isotope in the feces were sizeable, generally equal, and varied little in the different diseases studied, except in Paget''s disease. Calcium "pools" and compartment sizes as determined by either isotope proved to be sensitive indices of skeletal function. The largest values were found in Paget''s disease and thyrotoxicosis and the lowest in myxedema. There was no unusual pattern of labeled isotope excretion in patients with osteoporosis. Prolonged estrogen therapy in one patient with osteoporosis of the postmenopausal type effected no change in skeletal kinetics as measured by the metabolism of Ca45 or Sr85 but did effect a change in the serum to urine Ca45 specific activity ratio. The observation that Ca45 specific activities were consistently greater in serum than in urine and the variation of serum to urine ratios in different disease states is considered as representing either a true phenomenon or a systematic analytical error. Sr85 qualitatively parallels Ca45 as an index of skeletal function in metabolic bone diseases.