Influence of intrapelvic pressure on excretion of sodium from human hydronephrotic kidneys

The influence on urinary excretion of sodium (NNa . V) of intrapelvic pressure, urinary flow, and mean arterial blood pressure during forced diuresis was evaluated in 12 patients with unilateral hydronephrosis. Total and divided renal functions were measured using 51Cr-EDTA clearance and isotope renography. The amount of sodium, excreted by the obstructed kidney, decreased with higher maximum intrapelvic pressure and increased with higher differences between the mean arterial blood pressure and maximum intrapelvic pressure. The higher the concentrating ability, the lower the amount of sodium excreted by the obstructed kidney. There was a highly significant negative correlation between maximum intrapelvic pressure and urinary flow, but no correlation between mean arterial blood pressure and maximum intrapelvic pressure. Thus, obstructed kidneys with normal concentrating ability have the same excretion of sodium as the nonobstructed contralateral kidney during forced diuresis. Obstructed kidneys with decreased concentrating ability on the other hand excrete comparatively more sodium. This is probably due to a defect in sodium resorption.