Objective:To investigate the effects of unilateral ureteral obstruction on renal pelvic peristalsis and pacemaker cells in neonatal rats.Methods:An animal experimental study.Thirty-six 2-day-old newborn SD rats were randomly divided into the partial unilateral ureteral obstruction (PUUO) group, complete unilateral ureteral obstruction (CUUO) group, and sham operation group, with 12 rats in each group.One week after surgery, all rats were subjected to renal pelvic pressure (RPP) measurement by puncture.After measurement, the rats were euthanized, and their left renal pelvis and ureter were removed and fixed for histological examination.Parameters such as RPP, peristaltic wave frequency and amplitude at different perfusion speeds were recorded and compared, and the changes in pacemaker cells (atypical smooth muscle cells and Cajal-like interstitial cells) were also compared.The independent samples t-test was used for comparison between 2 groups, and the one-way ANOVA of variance was used for comparison among 3 groups. Results:In the sham operation group, the RPP increased gradually with the increase of perfusion speed; the frequency of peristaltic waves rose rapidly and then dropped after reaching the highest level with the increase of perfusion speed; similarly, the amplitude of peristaltic waves first increased and then decreased as the perfusion speed increased.In the PUUO group, the RPP increased rapidly with the increase of perfusion speed, higher than that in the sham operation group; the frequency of peristaltic waves was higher than that in the sham operation group, and it was relatively constant under the perfusion speed of 40 mL/h, but when the perfusion speed increased again, the frequency began to decline; the amplitude of peristaltic waves increased quickly and then declined at a faster rate than the sham operation group with the increase of perfusion speed.In the CUUO group, the basic RPP was 12 cmH 2O(1 cmH 2O=0.098 kPa); at the perfusion speed of 5 mL/h, the RPP rose gradually, and no plateau appeared; when the RPP reached 73 cmH 2O, the perfusate retrograded from the side of the puncture needle, then the RPP slightly decreased and then balanced, and no regular peristaltic waves were observed in the renal pelvis throughout the whole perfusion process.Immunofluorescence staining analysis showed the pacemaker cells were all located in the smooth muscle of the renal pelvic wall.The sham operation group had the highest positive rate, followed by the PUUO group and then the CUUO group. Conclusions:Ureteral obstruction has a significant impact on the peristalsis of the renal pelvis, and its impact on the peristaltic wave frequency and amplitude and RPP can be predicted.The reduction of pacemaker cells in the renal pelvis may be involved in the changes of renal pelvic peristalsis caused by ureteral obstruction, but further research is needed on how pacemaker cells regulate the peristalsis of the renal pelvis and ureter.