Although it has been established that acute expansion of the extracellular fluid volume results in enhanced uric acid clearance, the effect of chronic volume expansion by a high salt diet on urinary uric acid excretion has not been examined. Eleven normal subjects were placed on a constant diet containing 10 mEq. sodium per day for 10 days, followed by 240 mEq. sodium daily for another 10 days. Measurements were performed on the final 3 days of each phase. Urinary sodium increased from 9 plus or minus 3 standard error to 221 plus or minus 9 mEq. per day (p less than 0.001), and uric acid clearance increased from 5.9 plus or minus 0.4 to 7.1 plus or minus 0.6 ml. per minute (p less than 0.01). However, serum uric acid decreased from 6.4 plus or minus 0.4 to 5.5 plus or minus 0.3 mg/dl. (p less than 0.001). Total urinary excretion of uric acid did not change (533 plus or minus 24 to 535 plus or minus 26 mg. per day). A high salt diet does not result in sustained hyperuricosuria, although it may predispose to kidney stone formation in other ways.
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