Renal Excretion of Sodium During Oral Water Administration in Patients with Systemic Hypertension

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Abstract
The renal excretion of sodium and water was studied in 10 hypertensive subjects following an oral sustained 20 ml/kg water load. The study was performed under conditions controlled for sodium content of the diet, time of the day, and posture; the urine was collected by spontaneous voiding. The results were compared with those obtained from 10 normotensive subjects studied under similar conditions. The increased urine flow following the water load in the hypertensive subjects was not accompanied by increased excretion of sodium, a pattern similar to the one observed in the normotensive subjects. Comparing the group of hypertensive subjects with previously studied normotensives revealed the following additional information. The hypertensive subjects responded to water administration by increasing volume and C H H2 O more rapidly than the normotensives; however, the maximal response was not significantly different. The fractional reabsorption of sodium was less in the hypertensive subjects despite a lower filtered load of sodium. This suggests a difference in the renal tubular handling of sodium between hypertensive and normotensive subjects.