Partial ureteric obstruction in weanling rats. I. Long-term effects on the renal morphology.

Partial obstruction of one ureter was created in weanling rats (3 weeks old) and its effects were studied after 3, 6, and 9 weeks. Within 3 weeks, a considerable hydronephrosis had appeared, which did not progress with time. No effect on parenchymal weight was observed, either on the obstructed side or on the contralateral, intact one. Histological examination revealed a marked deformation of the papilla in about 25% of the hydronephrotic kidneys and evidence of chronic pyelonephritis in 40%. However, the inflammatory changes were restricted to the attenuated circumhilar 'edges' of the parenchyma, thus involving only a minor portion of the kidney. The body weight of the animals obstructed for 9 weeks was 12% lower than that of normal, sham-operated controls. In summary, the effect on the renal parenchyma of partial ureteric obstruction, created in the weanling period, was relatively discrete and less pronounced than when obstruction is performed in the neonatal period.