Effect of expansion of extracellular fluid volume on proximal sodium reabsorption in hyponatremic dogs

Abstract

The effects of infusions of equivalent volumes of saline solutions on proximal tubule sodium reabsorption and sodium excretion were studied in normonatremic and hyponatremic dogs. Similar expansion of the extracellular fluid volumes resulted in 48.1 per cent ± 3.63 per cent and 19.4 per cent ± 7.45 per cent decreases in proximal tubule reabsorption in the normonatremic and hyponatremic dogs respectively ( p < 0.005). Sodium excretions increased from 7.3 ± SE 1.78 μEq./min. to 289 ± SE 45.9 μEq./min. in normal dogs (p NA 144 mEq./L.) and from 3.1 ± 0.87 μEq./min. to 63.2 ± 23.0 μEq./min. in hyponatremic dogs (p Na 126 mEq./L.) following infusion of saline solutions. Expansion of the extracellular fluid volume of the hyponatremic dogs resulted in a significantly smaller decrease in sodium reabsorption by the proximal tubule and a significantly smaller increase in sodium excretion than in normonatremic dogs.