Quantitative ⁴⁵Ca autoradiography of human bone

Bone from 7 terminally ill men who received ⁴⁵Ca 1 2 to 23 days before death was studied by quantitative autoradiography. Short-term exchangeable calcium was located on bone surfaces, and had an apparent mass of 3.4 Gm. The time of maximal surface ⁴⁵Ca activity was 2.5 days. Diffuse activity of low intensity from long-term exchange accounted for 16.9 ± 3.3 per cent (mean ± S.E.) of total uptake; in the 2 patients having plasma ⁴⁵Ca measurements; the rate of diffuse uptake ranged from 10 to 25 per cent of the normal accretion rate. However, focal activity of intermediate intensity accounted for 49.8 to 68.4 per cent of uptake and was believed to be due to both long-term exchange and secondary mineralization. An unexpected finding was that 7.5 ± 1.6 per cent of activity was associated with bone resorption surfaces. Because of the terminal illness, bone formation was suppressed, and only 5.9 ± 2.4 per cent of activity was associated with hot spots.