Direct Measurement of Osteolysis in Man

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Precise, direct measurement of bone calcium release (vo-) has been accomplished using a continuous tracer administration (CTA) technique. Dietary calcium (96.97% 40Ca) is replaced by 40Ca (99.991% 40Ca) and blood levels of the naturally occuring isotope 48Ca are monitored by neutron activation analysis as a function of time. 48Ca abundance falls as this isotope is excreted and only partially replaced by release from bone. After a suitable period, an asymptotic abundance of 48Ca in serum, E, is approached which is the fraction of the turnover rate of the rapidly exchangeable calcium pools coming from the skeleton (E = vo-/vt). E is determined with a standard error of 2%, providing a precise, sensitive index of vo-. 13 studies in three normal men and one postmenopausal woman receiving maintenance estrogen show large intersubject variations in parameters of calcium metabolism using both CTA and pulse tracer administration (PTA) plus balance techniques. Induced hypercalcemia results in a prolonged decrease in vo-. Glucocorticoid therapy initially and consistently induces a marked hypercalciuria while effects on most other parameters of calcium kinetics are variable. In two men E fell when testosterone was added to glucocorticoid treatment, consistent with the known antiosteolytic effect of androgens, despite the short period of study.

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