Methods of testing urethral resistance in the female rat

Development of an animal model of stress urinary incontinence is dependent on a measure of urethral resistance, such as leak point pressure (LPP). However, animals will not cough or perform Valsalva maneuvers upon request. The aim of this study was to use urodynamics to compare bladder pressures during spontaneous voids (SV), anesthetized LPP measurement, and induced sneezing in female rats. A suprapubic catheter was implanted in the bladder dome of 10 female rats. Two days later, the rats were tested urodynamically under urethane anesthesia. The bladder was emptied and filled with saline. The abdomen was then depressed manually to increase abdominal pressure while bladder pressure was measured. The bladder pressure when leakage occurred was taken as LPP. In addition, the rats were stimulated to sneeze by cutting off a whisker and using it to tickle the nostril. Both peak pressure and increase in pressure during LPP (43.4 +/- 3.6 and 33.1 +/- 3.8 cm H2O, respectively) were significantly higher than pressures during both SV (30.4 +/- 3.8 and 19.3 +/- 3.4 cm H2O, respectively) and sneeze (9.5 +/- 0.7 and 2.6 +/- 0.5 cm H2O, respectively). The time course of a sneeze (0.6 +/- 0.2 sec) was significantly shorter than the time course of both LPP (4.4 +/- 0.5 sec) and SV (6.9 +/- 1.3 sec). No rat leaked from a sneeze unless the sneeze triggered an SV. LPP triggered a SV in 5 rats and sneeze triggered a SV in 6 rats. With urodynamic measurement, it is possible to easily distinguish between LPPs, SVs, and sneezes. LPP can provide a quantifiable measure of decreased urethral resistance, whereas induced sneezes can provide a diagnostic test for severe incontinence.