LONG-TERM BEHAVIOR OF RADIOSODIUM IN BONE - COMPARISON WITH RADIOCALCIUM AND EFFECTS OF VARIOUS PROCEDURES

Rats were given22Na intraperitoneally and the retention of the isotope was determined in whole body and in bone for periods up to 650 days. In contrast to45Ca, which is rapidly taken up by bone and then very slowly released, most of the22Na taken up by bone leaves, with a halftime of 3-5.5 days. However, about 5% of the skeletal burden exhibits a very slow turnover, with a half-time of about 700 days. Since this rate is comparable to that of45Ca, it is concluded that this small fraction of bone Na is an integral part of the crystal structure. Only two of the several experimental procedures which were tried produced a significant effect on bone Na turnover. These were prolonged feeding of a low calcium diet and a change in parathyroid activity. An increase in dietary Na affected the fast component of bone Na turnover, but there was little if any effect on the slow component. Calculations from our data suggest that, in contrast to Ca, the skeleton does not serve a significant reservoir function for the support of extracellular fluid Na. © 1969 Springer-Verlag.