Effect of renal pelvic and ureteral distension on the striated urethral sphincter with recognition of the "reno-vesico-sphincteric reflex".

Renal pelvic and ureteral distension occurs in physiologic (diuresis) and pathologic (calculus) conditions. Its effect on the vesical and posterior urethral pressures as well as on the electromyographic (EMG) activity of the striated urethral sphincter (SUS) was investigated. The renal pelvis of 10 healthy volunteers (7 men, 3 women; mean age 35.8+/-8.6 years) was distended by means of a 4-F balloon-tipped catheter in increments of 2 ml of saline up to 10 ml and the response of the vesical and posterior urethral pressures and SUS EMG activity was recorded. The test was repeated with ureteral distension in increments of 0.25 ml up to 1 ml. The response of the aforementioned parameters was also registered after anesthetization of the renal pelvis, ureter and SUS. Two rates of renal pelvic and ureteral distension were tested: rapid (1 ml/s) and slow (1 ml/min). Renal pelvic distension with large volumes effected an increase of the renal pelvic and urethral pressures (P < 0.05, P < 0.05, respectively), a vesical pressure drop (P < 0.05) and increased EMG activity of the SUS. Ureteral distension caused a rise of ureteral and urethral pressures as well as of SUS EMG activity. With rapid distension, the aforementioned parameters responded at smaller volumes than with slow distension. Renal pelvic, ureteral or SUS anesthetization effected no urethral or SUS EMG response. It is suggested that the reaction of above parameters to distension indicates a mechanism regulating the urine flow so as to protect the renal pelvis and the ureter from being overloaded. The vesical pressure drop with increased SUS EMG activity on renal pelvis distension postulates a reflex relationship that we call the "reno-vesico-sphincteric reflex". The role of this reflex in urine transport requires further study.