[Renal regulation of sodium excretion in experimental heart failure: study of hemodynamics and renal tubular...

This study was designed to evaluate the role of the kidney on sodium retention in congestive heart failure by clearance and hemodynamic studies. Twenty seven dogs were studied during hydropenia and aqueous diuresis 96 hours after the construction of a bilateral femoral A-V fistula, in 3 periods: 1) with open fistulae; 2) with closed fistulae and 3) with reopened fistulae. The animals retained sodium and water and developed edema during the first period when the fistulae were opened. Closure of the AV fistulae produced an enhanced diuresis and natriuresis associated with an increase in phosphaturia and distal sodium delivery, suggesting a diminished proximal sodium reabsorption. However, when the fistulae were reopened, sodium retention was observed in the presence of an increase in free-water clearance corrected by distal sodium delivery, indicating an increase in sodium reabsorption by distal segments. These findings were not associated with alterations in cortical distribution of renal blood flow. In conclusion, the sodium and water retention in congestive heart failure produced by A-V fistula is due to an increase in sodium reabsorption by the distal nephron segments, and it is not associated to a redistribution of the cortical renal blood flow.