VARIATION IN THE DIURETIC RESPONSE TO INGESTED WATER RELATED TO THE RENAL EXCRETION OF SOLUTES 1

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Abstract
Variations in the diuretic response to ingested water were studied in 10 subjects in whom water loads were established and maintained over periods of 4-9 hrs. When the subjects remained seated, the rates of urine flow and of Na excretion characteristically declined during the course of each expt.; when the subjects subsequently reclined, augmentation of urine flow and Na excretion was observed in 4 of 5 expts. The magnitude of diuresis was increased when the dietary intake of salt was large and decreased when antecedent salt intake had been restricted. The ingestion of NaCl, NaHCO3, KC1, NH4CI or urea was associated with an augmentation of urine flow and of solute excretion. The changes in urine flow were related to variations in renal tubular reabsorption of water rather than to glomerular filtration rate. The changes in urine flow were most consistently, although not invariably, related to parallel alterations in excretion of Na. It is suggested that alterations in the magnitude of water diuresis may be related to changes in Na excretion because, despite continued hypotonicity, contraction of effective extracellular volume evokes minimal ADH activity as well as decreased Na excretion; and tubular water is obligated differently by various solutes and the obligation imposed by Na is usually more important than that of other solutes.
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