High urinary flow accelerates renal injury in young rats with partial unilateral ureteral obstruction

Purpose: We studied the effect of dietary manipulation and high urine flow on neonatal partial ureteral obstruction in a weanling rat preparation. Materials and Methods: A total of 40, 3-week old Sprague-Dawley rats underw ent unilateral ureteral obstruction by burial of the right ureter in the ps oas muscle and 13 underwent. sham operation. Low, high and normal salt, and high sucrose diets were administered for 2 months. The glomerular filtrati on rate of each kidney was measured by iothalamate clearance. Intrapelvic p ressure and renal blood flow were measured before and after acute volume lo ading. Results: Fluid intake and urine output were 8 to 10-fold greater in animals on high salt and high sucrose diets compared to those in rats on normal an d low salt diets. Hydronephrosis was observed only in rats with partial obs truction and high urine flow. No difference in renal weight was noted. Rela tive glomerular filtration rate of the partially obstructed kidney was main tained when urine flow was normal but decreased significantly with high uri ne flow. Total glomerular filtration rate also decreased with high urine fl ow. Intrapelvic pressure was elevated significantly at baseline in partiall y obstructed kidneys with high urine flow. All kidneys with partial obstruc tion had significantly increased intrapelvic pressure with volume loading. Renal blood flow was not significantly decreased in rats with high urine fl ow. Conclusions: Chronic high urine flow causes loss of renal function in parti ally obstructed weanling rat kidneys. Research should be done to determine whether human infants with hydronephrosis and partial ureteral obstruction would benefit from the prevention of increased fluid and salt intake.