The Participation of Bone in the Sodium and Potassium Metabolism of the Rat. I

A method is described whereby total exchangeable sodium and potassium in the rat is simultaneously determined by the use of istope dilution techniques. These measurements have been combined with the determination of the total and exchangeable concentrations of sodium and potassium in bone, made possible by a new procedure employing cation exchange resin for isolation of the bone electrolytes. Series of normal 100 g rats, 200 g rats and 300 g rats were examined. The results for the total body content of sodium and potassium obtained in these animals agreed with published data from total body ashing procedures. Total bone sodium concentration increased with age, whereas the concentration of the exchangeable fraction was rather constant in the three groups. The exchangeability of the bone sodium was 71 per cent in the 100 g rats and 56 and 50 per cent in the 200 and 300 g rats. Bone potassium concentration was highest in the 100 g rats; the exchangeability of this ion in bone was 80 per cent in this group and close to 100 per cent in the two other groups. The complete set of figures is given in Table III.