POSTURAL EFFECTS ON RENAL TUBULAR ACTIVITY 1

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Abstract
The effects of posture on urine flow, free water clearance, osmolar clearance, endogenous creatinine clearance and Na excretion were determined in normal subjects in maximal water diuresis. It is assumed that distal water reabsorption is abolished and that proximal reabsorption is isosmotic. The findings are interpreted to mean that a higher percentage of the filtered water and Na is reabsorbed proximally on standing than on lying and that a lower percentage of the filterec Na (and a lower absolute amount per unit time) is reabsorbed distally on standing. The percentage reabsorbed of the distally delivered Na load is the same for lying and standing. Slightly lower endogenous creatinine clearance values were observed on standing, although the differences between standing and lying were less than are seen at urine flows below maximum. The percentage changes in creatinine clearance were less than in excretion of water and Na and in free water and osmolar clearances.