Relationship of Mass of Obstructed Rat Bladders and Responsiveness to Adrenergic Stimulation:

Decreased Monoamine Oxidase A Expression and Activity in the Bladders of Rats With Partial Outlet Obstruction

OBJECTIVE

To investigate changes in expression and activity of monoamine oxidase A (MAO-A) in rats with partial bladder outlet obstruction (pBOO). Previous studies suggested that monoamines, such as serotonin (5-hydroxytryptamine [5-HT]) and noradrenaline, are involved in bladder hyperactivity secondary to pBOO. However, little is known about the role of MAO-A, an enzyme oxidizing 5-hydroxytryptamine and noradrenalin, in the pathogenesis.

MATERIALS AND METHODS

Female Sprague Dawley rats were subjected to sham or pBOO operations for 7 days, then their bladders were isolated. MAO-A protein levels in the bladder were examined by Western blotting. MAO-A activity was measured by the commercially available MAO-Glo Assay kit. In addition, MAO-A distribution in the bladder was examined by immunohistochemistry.

RESULTS

Weights of the bladders from rats with pBOO were increased about 3.5-fold, compared with those from sham rats. Significant decreases in MAO-A protein and activity levels were observed in whole bladder of rats with pBOO compared with those of sham rats. By immunohistochemistry, it was firstly demonstrated that MAO-A was predominantly expressed in the detrusor layer of the sham rat bladders. The intensity of staining was decreased after pBOO operation.

CONCLUSION

We demonstrated, for the first time, the distribution of MAO-A in the bladder and the pathologic changes in MAO-A protein and activity levels in rats with pBOO. This marked decrease in MAO-A potentially resulting in increased monoamine levels, especially in the detrusor of rat bladder, might be a key factor explaining the mechanism of bladder overactivity associated with pBOO.

Effects of Selective Alpha-1-Adrenergic Receptor Blockers on Bladder Weight

INTRODUCTION

This study was undertaken to investigate the effects of two different alpha(1)-adrenergic blockers on bladder hypertrophy using ultrasound-estimated bladder weight (UEBW) and to assess the relation between changes in UEBW and other objective and subjective parameters of disease severity in patients with benign prostatic hyperplasia (BPH).

MATERIALS AND METHODS

41 men were enrolled in the study and they were subjected to either watchful waiting (group 1) or alpha(1)-adrenergic receptor blocker therapy (group 2 with alfuzosin; group 3 with tamsulosin). The patients were investigated by symptom evaluation using the International Prostate Symptom Score (IPSS) and quality of life score (QOL), uroflowmetry and UEBW. The parameters were assessed again 3 months after initiation of treatment and compared with the initial values.

RESULTS

While the mean UEBW increased in group 1 (42.2 +/- 10.3 to 52.5 +/- 12.2 g), it decreased in both the other groups that received alpha-blocker therapy (61.3 +/- 18.7 to 41.1 +/- 13.2 and 59.4 +/- 17.2 to 43.5 +/- 17.6 g, respectively). In groups 2 and 3, the mean UEBW, post-void residual urine, IPSS and QOL values decreased, and the mean maximum flow rate increased. All of the changes in group 2 and all except QOL in group 3 were statistically significant (p < 0.05). The changes correlated well with each other with regard to treatment success. The highest decreases in UEBW were encountered in patients with heavier bladders.

CONCLUSIONS

UEBW decreases with alpha(1)-adrenergic receptor blockers. When used together with the other objective and subjective parameters, UEBW is a promising quantitative parameter as a follow-up tool and can be useful in monitoring the therapeutic effects of alpha(1)-adrenergic receptor blockers.

Regional differences in responses of rabbit detrusor to electrical and adrenergic stimulation: influence of outlet obstruction

OBJECTIVE

To examine regional responses of control and obstructed rabbit detrusor strips to electrical and adrenergic stimulation, and determine whether outlet obstruction causes regional variations in blood flow throughout the detrusor, as the detrusor smooth muscle of the bladder body has previously been considered homogeneous in its pharmacological properties.

MATERIALS AND METHODS

Fourteen male rabbits had the bladder outlet surgically obstructed for 2 weeks and were compared with 10 unoperated control rabbits. Blood flow was measured with the bladder empty and at capacity, using fluorescent microspheres. Paired dorsal and ventral strips were harvested from the midline equatorial detrusor and electrically and adrenergically stimulated.

RESULTS

Obstructed rabbits had significantly higher bladder capacities and bladder weights than control rabbits. Dorsal strips from both control and obstructed rabbits contracted in response to noradrenaline, whereas ventral strips relaxed. The addition of prazosin, a nonselective alpha1-adrenergic-receptor blocker, completely blocked the contraction in dorsal strips, but had no effect on responses of ventral strips. There was also a regional difference in response to electrical stimulation, with ventral strips generating significantly more tension than dorsal strips in both control and obstructed rabbits. There were no regional differences in detrusor blood flow. Obstruction resulted in significantly lower responses to all forms of stimulation, and significantly less blood flow throughout the detrusor.

CONCLUSION

There are regional differences in adrenergic receptor function and response to electrical-field stimulation throughout control and obstructed rabbit detrusor, a region that was previously thought to be functionally homogeneous. These differences must be recognized and acknowledged to obtain accurate and reproducible data from in vitro studies of the bladder.