Renal Function and Metabolism After Relief of Unilateral Ureteral Obstruction

Abstract

Renal handling of electrolytes and water may be altered following the relief of obstructive uropathy with increased excretion of salt and water. Mechanisms proposed to explain this increased salt and water excretion include retention of solutes (1), production of a natriuretic material during obstruction (2), and expansion of the extracellular fluid volume (3). In addition, it has been postulated that structural damage to the kidney may also play a role in the altered handling of electrolytes and water (2).

Recent observations demonstrating increased fractional excretion of salt and water following release of unilateral ureteral obstruction in experimental animals (4) indicated that structural damage or some other intrinsic change within the kidney may be responsible for the altered electrolyte and water handling. The presence of a contralateral normal kidney during the period of obstruction would prevent extracellular fluid volume expansion and solute retention during the period of obstruction, and thus exclude these as major factors in the altered excretory pattern of electrolytes and water. It has been suggested that structural alterations such as flattening of proximal tubular microvilli (5) will decrease the total luminal surface area of the epithelial cells which makes contact with the tubular fluid and thereby decrease tubular reabsorption (2). Of interest is the fact that certain histochemical alterations are observed following obstruction. Alkaline phosphatase has been found to be greatly reduced (6, 7) while glucose-6-phosphate dehydrogenase and 6-phosphogluconic dehydrogenase activities were increased in the proximal tubules of obstructed kidneys (8). Following release of obstruction the activity of these enzymes remained elevated during the initial 48 hr and returned to normal 6 days postobstruction. Decreases in Na-K ATPase activity also have been described following obstruction of 48-72 hr duration (9). Despite these observations, little attention has been paid to the possible role of renal metabolic alterations in the handling of electrolytes and water following relief of obstruction.