STUDIES ON FUNCTION OF THE UPPER URINARY TRACT

VIII. The Peristaltic Activity during Induced Diuresis in the Pelvi-ureteral System in Dogs

Abstract

The present investigation was undertaken in order to clarify the mechanism of the transport of urine by the pelvi-ureteral system in dogs. Twenty-eight preparations of exteriorized renal pelvis and ureter from 18 dogs were used. Dogs were operated under thiopental anesthesia. The pelvis and ureter were exposed transperitoneally, and electrodes were implanted at the pelvis and ureter. Simultaneous recordings of pelvic and ureteral myograms were obtained.
A vein needle connected to a pressure transducer was placed in the pelvis and pressure within the pelvis was recorded. For mesurement of intraureteral pressure, a No. 18 gauge scalp vein needle was inserted into the ureter below the site of implanted electrode.
These measurements were made simultaneously with myogram recordings. The changes in pelvic and ureteral peristalsis were recorded, together with the corresponding myogram and pressure recordings after rapid diuresis induced by an intravenous infusion of Furosemide (10-20mg). Results:
1) The average frequency of contraction before induced diuresis was 24. 6 times per min. in the pelvis and 8.7 times per min. in the ureter. Namely, the peristaltic frequency of the pelvis before diuresis was greater than that of the ureter by a ratio of 3: 1.
2) During diuresis, the average frequency of contraction was 24.1 times per min. in the pelvis and 22.7 times per min. in the ureter, indicating that the peristaltic activity of the ureter increased as the urine volume increased.
3) The frequency ratio of 1: 1 seen during diuresis remained unchanged for 7 min. and 25 seconds. Subsequently it returned to the pre-infusion level.
4) Pressure within the pelvis showed low and continuous contraction waves corresponding to the amplitudes of pelvic contraction before and after the Furosemide-induced diuresis. In the ureter, however, the high contraction waves corresponding to the amplitude of ureteral contraction were seen. During diuresis, both the standing and contraction pressures within the pelvis and ureter were equally elevated.
The results of the present investigation suggest that the intact pelvis continues a rhythmical contraction, despite the absence of urine, and no peristaltic activity is accelerated in the ureter unless urine in the pelvis passes through the pelvi-ureteral junction to reach the ureter. During marked diuresis, distension of the pelvi-ureteral junction occurs as the intrapelvic pressure increases. Subsequently, the frequency of ureteral peristaltic contractions increases as the ureter at the pelvi-ureteral junction is dilated by urine pressure. At this diuretic stage, the capacity of the ureter to adjust itself to changes in urine volume is limited by its inability to dilate beyond a certain point. Therefore, the increased frequency of ureteral peristaltic contraction expels a larger volume of urine to minimize outflow resistance, thereby reducing back pressure toward the kidney.
The data presented would be prerequisite for the better understanding of the pelvi-ureteral function in man.