An electro-myographic study of the distal porcine ureter

Purpose: The accumulation of urine in the renal pelvis causes depolarisation of non-specific muscular pace-maker cells. The wave of depolarisation spreads distally in the ureteric smooth muscle cells via gap junctions. This wave of excitation causes a coordinated peristaltic contraction which transports the urine bolus distally to the bladder. The EMG activity in the distal porcine meter was studied and analyzed to establish the characteristics of ureteric excitation. Materials and Methods: Ten female New Yorkshire pigs (50 to 60 kg.) were studied in two groups under light halothane anesthesia (5% at induction and 1% for maintenance anesthesia). In both groups each pig was studied in two separate sessions at a week's interval. In group I (n = 5), bipolar needle electrodes (empty set: 0.09 mm.) were implanted through a lower mid-line abdominal incision in the posterior bladder wall, the trigone and the pelvic ureter at intervals of 3 and 8 cm., respectively, from the ureteric orifice. In group II (n = 5), EMG spike burst activity was studied using a twin bipolar ring-electrode attached to an endoluminal ureteric catheter, EMG complexes were recorded using 0 to 30 Hz filters. The duration of spike burst complexes and their intervals were analyzed using a Nicollet, Pathfinder II(R) machine and a Poly(R) 4.9 digital signal processing program. Results: Two types of spike burst activity could be distinguished between the electrodes: A, the migrating type and B, the non-migrating type. Frequency distribution analysis of spike burst duration revealed two main classes in experimental group II, a short spike burst (96%) which lasted 4.5 +/- 1.8 seconds and a longer one lasting 13.4 +/- 1.5 seconds. The conduction velocity of the migrating spike bursts (n = 177, 42% of total) between the proximal and the distal electrode had an average of 2.3 +/- 1.3 cm./sec. No relationship was found between the duration of the proximal spike burst and the conduction velocity. Data from experimental group I correlated well with data from group II. Conclusions: The results of our EMG study in the distal ureter reveal an approximately 9 cm. long electrically active zone in greater than or equal to 90% of EMG activity recordings. The duration of activity was approximately 5 seconds. Such an excited segment of meter led to a contraction which occluded the ureter and could prevent retrograde leakage of intraluminal contents.