Abstract
Calcium (Ca) disorders and therapeutic effectiveness can be assessed by measurements of bone dynamics using stable tracer methods. A pulse of IV Ca-46 is followed by a 9-15 day continuous feeding of Ca-48. Ca isotopic abundances in serum, urine, and feces are determined by thermoionization mass spectrometry (0.5% precision). Kinetic parameters (mg/kg/d) are calculated by nonlinear, weighted least squares analysis and growth is compensated for by using expanding pool sizes. Two infants (Inf.) had Ca turnover rates 12 times that of a control adult (Ad); bone Ca deposition (vo+) and resorption (vo-) were determined with 2 to 5% precision. Two infants with osteogenesis imperfecta (OI) were studied before (B) and while taking ascorbic acid (C). Inf show excessive endogenous fecal (vf) to urinary (vu) Ca excretion as compared to adults, suggesting a major role for vf in regulating Ca balance in Inf. An Inf with OI had similar Ca dynamics except for a decrease in bone Ca fluxes. Ascorbic acid, as suggested for clinical use, had no effect on bone calcium balance.
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