INFLUENCE OF SODIUM INTAKE ON EXCHANGEABLE SODIUM IN NORMAL HUMAN SUBJECTS*

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Abstract
In 5 subjects given 15 [mu]c Na22 and followed with measurements of body radioactivity and serum Na specific activity, changes in Na intake from 1-2 meq to 181-359 meq daily resulted in a significant increase in calculated exchangeable Na. There was no discernible contribution of a slowly exchanging Na pool to these measurements. There was prolonged retention of a small fraction (less than 1%) of the tracer dose, consistent with its incorporation into bone. Almost identical exchangeable Na values were obtained with Na24 at 24 hours as with Na22 at 2 to 3 months in 1 normal and 2 edematous patients. It was concluded that long-term Na balances were feasible with this technique in that changes in the values would accurately reflect changes in the metabolically active Na pool.