Purpose: To create an animal model with mild and severe partial unilateral ureter obstruction in young rats using a modified Ulm and Miller technique and to characterize the model by acute renal pelvic pressure measurements.
Material and methods: During anesthesia the upper fourth (n = 15) or the upper two-thirds of the left ureter (n = 15) was embedded into the psoas muscle causing either a mild or severe partial obstruction. Sham-operated control rats were prepared in parallel (n = 20). The baseline pelvic pressure, the perfusion pelvic pressure (perfusion rates: 0.2 to 1.0 ml. per minute) and peristaltic waves were recorded after a resting period.
Results: Mean baseline pelvic pressure and perfusion pelvic pressure were significantly higher in obstructed kidneys than in non-obstructed kidneys, and significantly higher in severely obstructed kidneys than in mildly obstructed kidneys (p < 0.05). A fair linear relationship existed between the increase in pelvic pressure and the increase in perfusion rates in all groups. In the severely obstructed kidneys, baseline pelvic pressure was 16.9 +/- 2.3 cm. H2O and the perfusion pelvic pressure increased significantly from 41.7 +/- 3.3 cm. H2O to 68.6 +/- 6.3 cm. H2O. The pelvic peristaltic amplitude increased significantly following the increase in perfusion rate and there was a significant difference in the amplitude between severely obstructed and non-obstructed kidneys when the perfusion rate exceeded 0.4 ml. per minute (p < 0.05).
Conclusion: Embedding either the upper fourth or the upper two-thirds of the ureter into the psoas muscle produced a mild or a severe partial obstruction. In the latter model a significant increase in pelvic pressure and amplitude was observed, indicating the existence of severe obstruction.