An application of neutron activation and radiotracer techniques for studying the status of sodium in the bone mineral.

Neutron activation analysis of intact and water-extracted (on boiling) bone (femur) samples made it possible to determine manganese, sodium, potassium and chlorine. A major portion of sodium in contrast to potassium) was retained in the bone, which was in agreement with a well known presence of slowly exchangeable sodium in the bone. Further experiments were carried out with fragments of the femur of rabbits that were administered with the radionuclide 22Na and sacrificed after a sufficient equilibration period. Under conditions of stirring with water at a laboratory temperature, a two-exponential course of the sodium ion release was observed with half time values of 4.36 and 167 hours. An explanation is suggested that in the bone there are actually two fractions of slowly exchangeable sodium, present on the bone mineral crystal surface and bone mineral crystal interior, respectively. The experiments on the bone in vitro can help to bridge a gap between in vitro experiments on synthetic hydroxy apatite and dynamic studies based on the in vivo neutron activation analysis. Results of a complementary experiment with ashed bone samples demonstrated an almost complete abolishment of the sodium ion release, which is in perfect agreement with a known concept of the thermal recrystallization of the bone mineral.