Chronic Hydronephrosis: Observations on the Mechanism of the Defect in Urine Concentration (34850)

The renal concentrating and diluting mechanism was examined in dogs with unilateral chronic hydronephrosis and compared to the contralateral normal side. Urine concentrating ability and concentrating capacity were markedly impaired in the chronically hydronephrotic kidney. However, as previously reported, fractional free water clearance over a large range of distal delivery was identical in both kidneys. Significant reductions in papillary and medullary nonurea solute concentration were present in the hydronephrotic kidneys as compared to controls during both hydropenia and hydration. It is postulated that reduction in the number of functioning nephrons in the medulla results in a decrease in sodium transport into the interstitium and, therefore, in reduced medullary hyper tonicity. This, by decreasing free water back diffusion out of the collecting duct, would result in the impaired urinary concentrating ability and capacity observed in chronic hydronephrosis.