Sequential renography and renal function in Brown-Norway rats with congenital hydronephrosis

Animal models may be helpful to gain insight into the long-term functional outcome of the hydronephrotic kidney. Inbred Brown-Norway rats frequently have kidneys with a delayed urine outflow. In 26 male rats 99mtechnetium-diethylenetriaminepentaacetic acid (Tc-DTPA) furosemide renography was performed to assess the presence and degree of obstruction, and the contribution of each kidney to the total glomerular filtration rate. The total glomerular filtration rate was measured as the plasma clearance of 51chromium-ethylenediaminetetraacetic acid. The measurements were first done at the age of 3 months, and repeated at ages 6, 10 and 15 months. From the renography curve we derived an obstruction score ranging from 0 (minimum) to 10 (maximum) based on the time to peak, the 99mTc-DTPA accumulation at 15 minutes and the furosemide response. Kidneys were classified as normal, obstructed or equivocal. At the first renography 21 kidneys were normal, 8 were equivocal and 23 were obstructed. The total obstruction score of the next 3 renographies indicated that 29 units were normal, 14 were equivocal and 9 were obstructed. Two groups of rats with unilateral hydronephrosis (hydronephrotic kidney-1 and hydronephrotic kidney-2) were selected based on the total obstruction score of all 4 renographies. These groups were compared with rats with 2 normal kidneys. The hydronephrotic kidney-1 rats had an obstruction score indicating equivocal obstruction, while the obstruction score of the hydronephrotic kidney-2 rats indicated obstruction. During the 15 months of followup the presence of a unilateral hydronephrotic kidney with an obstruction score indicating obstruction did not affect the contribution of the hydronephrotic kidney to the total glomerular filtration rate, or the total glomerular filtration rate. We conclude that the obstruction score of a hydronephrotic kidney in rats may change considerably with time. In cases in which renography suggested the permanent presence of ureteral obstruction the glomerular filtration rate remained stable. Thus, renal functional criteria did not indicate obstruction. In Brown-Norway rats a hydronephrotic kidney is able to maintain a normal glomerular filtration rate during at least 50% of the normal lfie span.