Maximum physiological concentration of sodium in human urine

Abstract

Six apparently normal young men received salt intakes of up to 540 mEq/day, or more, with free access to water. The five subjects who tolerated these high intakes drank enough water to maintain the sodium concentration in the 24-hour urine specimens at a mean of 268 mEq/l. with a range of means in the individual subjects of 240–295 mEq/l. Under these circumstances there was little change in the size of the body fluid compartments. The results indicate that there is a maximum physiological concentration of sodium in the urine, probably in the range of 270–290 mEq/l., which is similar to the ‘limiting isorrheic concentration’ described by Wolf. ( The Urinary Function of the Kidney. New York: Grune, 1950.) Submitted on July 16, 1959