Renal structural and functional changes after unilateral ureteral obstruction in rabbits

Renal structural and functional changes following unilateral ureteral ligation for periods of 3 days to 6 weeks were studied in rabbits. The renal pelvic pressure increased to 20 cm H2O within 3 days of obstruction and in contrast to some previous investigations it was still raised after 6 weeks. Interstitial oedema, collapse of proximal tubules and dilatation of distal tubules were the earliest observed histological changes. Later findings were interstitial fibrosis, widespread atrophy of proximal tubules and, in the latest stages, dilatation of the collecting duct system. Thus, the distal tubules appeared considerably less resistant than the collecting ducts, to the increased pressure. Renal functional changes were studied one hour after release of obstruction of 3 days, 1-2-4 or 6 weeks' duration. In comparison to the contralateral kidney a rapid decrease of blood flow and glomerular filtration occurred in spite of a normal glomerular structure and collapsed proximal tubules and were probably related to haemodynamic disturbances such as arteriolar constriction. Although absolute electrolyte excretion was much reduced, the fractional excretion of several electrolytes, especially magnesium was increased already after 3 days of obstruction. These findings can presumably be correlated to the dilatation and early epithelial alterations in the distal tubules in which magnesium is predominantly reabsorbed.