Hemodynamic changes after complete unilateral ureteral obstruction in the young lamb

Purpose: We studied renal hemodynamic changes ai?ter complete acute unilateral ureteral obstruction in the young lamb. Materials and Methods: Seven 4-week-old lambs underwent unilateral complete ureteral obstruction and renal blood flow was monitored in both kidneys with ultrasonic flow transducers. Ureteral and arterial blood pressure was measured, Results: In the obstructed kidney renal blood flow was stable for 5 hours and then decreased thereafter to 71% of baseline at 5 days (p <0.05). In the contralateral kidney the pattern of renal blood flow constituted a mirror image, although the magnitude of the increase was decreased (122% of baseline at 5 days, not statistically significant), Mean arterial blood pressure did not change in 5 days, Mean ureteral pressure increased from a baseline of 9 to 37 mm. Hg (p <0.001) 2 hours after obstruction but gradually decreased to 24 mm. Hg after 24 hours and remained elevated for 5 days (p <0.001). Conclusions: The pattern of renal blood flow and ureteral pressure response to obstruction in the young lamb is different from that previously reported. Renal blood flow does not increase after obstruction and it is relatively preserved at 5 clays. This unexpected response may be a result of the compound caliceal sheep kidney, immaturity of the young vascular system or developmental differences in the mechanism of spontaneous decompression of the collecting system.