Groups of young and old rats were injected with a variety of labelled substanzes (urea, CI-, K+, Na +, HCOa-, PO~-, Ca++). Data for Mg++ were taken from the literature. One and a half hours later, compact shafts of long bones were removed and cleaned scrupulously, and analyses were performed for both" cold" and isotopic concentrations of substances. This time point was chosen to insure equilibration of the aqueous phase of bone while minimizing contributions from surface exchange, recrystallization, solid diffusion, growth or resorption.With fixed variables of time, species, bone specimen, and methodology, uambiguous comparisons of the exchange in bone could be made between the many substances studied. The exchange data could be divided into three categories: a) complete exchange (urea CI-, and K+); b) partial exchange, decreasing variably with age (Na +, CO~, and Mg++); and c) minimal exchange (Ca ++ and PO~-). Clearly the traditional classification of "available" and "unavailable" skeleton is ambiguous and determined by the conditions and the ion or substance chosen for study. Clearly also, a new overall concept of bone exchange in vivo is badly needed.Calculations of the apparent concentration of the various electrolytes in bone water reveal that the aqueous phase of bone has a composition markedly different from plasma water. In particular, the concentration of potassium in bone water was found to be remarkably high.Key words: Mineral --Exchange --Bone --Isotope --Radioactive-Autoradiography.Des prodnits marqu6s vari6s (ur6e, CI-, K +, Na +, HCO~, PO~-, Ca ++) sent administr6s /~ des groupes de rats jeunes et t~g6s. Les r6sultats pour Mg ++ sent emprunt6s a ceux trouv6s darts la litt6rature. Une heure et demie plus taM, des fragments d' os longs sent pr61ev6s et nettoy6s minutieusement. La concentration de ces substances marqu6es et non marqu6es est d6termin6e. L'intervalle de temps choisi est utilis6 afin de permettre l'6quilibre de la phase aqueuse de l'os, tout en r6duisant les 6changes de surface, la recristallisation, la diffusion solide et la croissance ou la r6sorption.Avec des intervalles de temps fixes, avec les m~mes espbces ainsi que des specimens osseux et des techniques identiques, une comparaison des 6changes entre les divers es substances darts l'os a pu ~tre effeetu6e. Les r6sultats ont pu 8tre r6partis en trois groupes: a) 6change total (ur6e, C1-et K+); b) 6change partiel, diminuant de fa~on variable avee l'age (Na +, CO2 et Mg++); et c) 6change faible (Ca++ et PO~-). La classification classique de sequelette ~accessible,~ et ~non accessible ~> parait peu conforme et d6pend des conditions et de la nature de la substance 6tudi6e. Un concept g6n6ral des 6changes osseux in vivo devrait gtre 6labor6.Des calculs coneernant la concentration apparente des divers electrolytes au niveau de la phase aqueuse de ros montrent qu'elle a une concentration nettement diff6rente de celle du plasma. La concentration du potassium y est, en particulier, remarquablement 61ev6e.Gruppen von jungen und alten Ratten ...
