Influence of volume expansion on proximal tubular sodium reabsorption in congestive heart failure

Proximal tubular sodium reabsorption was studied in ten patients with severe decompensated congestive heart failure when marked extracellular fluid volume expansion was present and again after diuresis to dry weight. The technique used was pharmacologic blockade of distal nephron sites by diuretic agents. The percentage of the filtered load of sodium reabsorbed by the proximal tubule increased from 68 ± 5 per cent to 85 ± 2 per cent and of chloride from 61 ± 6 per cent to 78 ± 4 per cent following reduction of the expanded extracellular volume. This increase could not solely be accounted for by change in filtered sodium load or enhanced aldosterone activity. It is concluded that although the proximal tubule responds in an appropriate manner qualitatively to volume stimuli, an enhanced fractional proximal sodium reabsorption at any given level of extracellular fluid volume may characterize the patient with congestive heart failure. The exact mechanism of sodium retention in heart failure must remain speculative.