Direct measurement of osteolysis in man

Precise, direct measurement of bone calcium release (v(o-)) has been accomplished using a continuous tracer administration (CTA) technique. Dietary calcium (96.97% (40)Ca) is replaced by (40)Ca (99.991% (40)Ca) and blood levels of the naturally occuring isotope (48)Ca are monitored by neutron activation analysis as a function of time. (48)Ca abundance falls as this isotope is excreted and only partially replaced by release from bone. After a suitable period, an asymptotic abundance of (48)Ca in serum, E, is approached which is the fraction of the turnover rate of the rapidly exchangeable calcium pools coming from the skeleton (E = v(o-)/v(t)). E is determined with a standard error of 2%, providing a precise, sensitive index of v(o-). 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 v(o-). 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.