Assay of bone resorption in vivo with3H-tetracycline

Abstract

³H-Tetracycline (³H-TC) was used to quantify resorption in whole bones of growing rats and dogs. After repeated isotopic labeling of actively growing embryos or neonates,³H-TC was observed to be distributed homogeneously and in equilibrium with⁴⁵Ca. A rapid and large loss of³H-TC and a small loss of⁴⁵Ca occurred during the early weeks of rapid bone growth, suggesting thatabsolute amounts of⁴⁵Ca resorbed from bone, as reflected by losses of³H-TC, are five to ten times greater than thenet amounts of⁴⁵Ca lost from bone. Minimal loss of³H-TC occurred due to nonspecific physicochemical exchange in vivo or in vitro (5%) except with nonradioactive tetracycline, and³H-TC was not greatly exchanged or reused (10%) in vivo. The data are considered in terms of local and systemic conservation of calcium.