Effect of Age on Radiosodium Exchange in Bone (Rat)

¹ From the Department of Pediatrics, University of Rochester School of Medicine and Dentistry, Rochester, New York

On a wet weight basis, bone from young animals contains more water and chloride, and less sodium and calcium than that of the adult. In the young animal, a much larger fraction of the skeletal sodium exchanges readily with radiosodium. However, since the skeleton of the older animal has a much higher sodium concentration, the total amount of sodium per unit skeletal weight which is available for exchange does not vary appreciably with age. Sodium in bone is considered metabolically to consist of three phases: 1) ‘fluid’ phase sodium, represented by that contained in the chloride space; 2) the exchangeable portion of the ‘crystal’ phase Na; and 3) the nonexchangeable Na of the ‘crystal’ phase. Changes in the magnitude of each of these phases occurs during growth in the rat.