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

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.

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.

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.

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.