Bladder mechanoreceptor changes after artificial bladder outlet obstruction in the anesthetized rat.

AIMS: Experimental animal models of bladder outlet obstruction (BOO) have reproduced several features of BOO in man, i.e., detrusor hypertrophy, instability, frequency, and residual urine. This study was focused on the mechanisms underlying the development of residual urine in patient with benign prostatic hyperplasia (BPH) by examining changes in tension sensitivity of bladder mechanoreceptors in rat model.

METHODS

Female adult Sprague-Dawley rats including 12 BOO and 17 sham operated rats were used in this study. Cystometrograms together with the bladder afferent activity were recorded. Tension sensitivity of the afferents was determined by plotting the normalized afferent response against the contraction evoked bladder pressure at different volumes. Degree of obstruction was assessed by the wet weight of the bladder at the end of the experiment.

RESULTS

The bladder weight, maximal bladder capacity, micturition threshold volume, peak contraction force, and volume at peak contraction force were all significantly increased in obstructed animals. The threshold volume for afferent activation was increased (mean 0.60 ml compared to 0.15 ml in controls; P < 0.001), positively correlated with the bladder weight (r = 0.74). The tension sensitivity of the bladder mechanoreceptors and the slope of their normalized pressure-response functions were significantly lower at the comparable volumes in the obstructed animals.

CONCLUSIONS

Rats with BOO had bladder mechanoreceptors with higher threshold volumes and lower tension sensitivity. Such changes would result in a weaker afferent drive of the micturition reflex. Similar changes may contribute to the development of residual urine and retention in patients with BOO.