The effect of unilateral ureteral obstruction on the contralateral renal growth in weanling rats

: The effect of unilateral hydronephrosis on the growth of contralateral kidney were evaluated with weanling rats of which kidneys were in growing stage (body weighted between 80 g and 90 g). These rats underwent complete unilateral ureteral obstruction (CUUO) on day 0. They were divided into 3 groups and went through second operations on day 3 (CUUO-3) as follows; a) CUUO released, b) nephrectomy performed and c) CUUO continued. Sham-operation was performed on day 0 and on day 3 to the controls. Wet weights and bromodeoxy-uridine (BrdU) labeling index (L.I.) (index for cell proliferation in the uriniferous tubules) of the contralateral kidneys were measured for the evaluation. The wet weights were significantly higher in all the groups than that of the controls throughout the observation period on and after the day 3. The group that underwent nephrectomy demonstrated a sharp rise in L.I. after the day 7. In the group that was continued in CUUO, the L.I. started to rise later than its rise in nephrectomised group but the index caught up at the time when the blood flow completely disappeared in the kidneys of the ligated side. L.I. in the group of which CUUO was released became significantly higher than that of controls on the day 7 and remained its significance until the day 21 in spite of resolution of the hydronephrosis. To reveal the effect of length of obstructed term, the same trial was carried out that rats endured in CUUO for 5 days (CUUO-5) till the second operation. This turned out lower L.I. in the CUUO-5 than the CUUO-3. These results suggest that the presence of hydronephrosis made by CUUO suppress the growth (cell proliferation) of contralateral kidney and also duration of obstruction can be critical on the renal growth that shorter obstructed period turns out preferable for cell proliferation after relief of CUUO.