Effect of strip length on the contractile dysfunction of bladder smooth muscle after partial outlet obstruction

Partial outlet obstruction mediates decreased contractile responses and increased collagen synthesis; however, it is not known to what extent the increased collagen contributes to contractile dysfunction.

Sixteen WNZ rabbits were divided into three groups: control, 2-week obstructed, and 2-week sham. Each rabbit was anesthetized, and the bladder was excised and cut into equal width strips of 0.5, 1.0, and 2.0-cm lengths. The contractile responses to field stimulation, carbachol, potassium chloride, and adenosine triphosphate were determined. At the end of the experiment, each strip was fixed in formalin and immunostained for collagen.

The contractile responses for the control and sham strips were similar for all strip lengths. In obstructed tissue, the shorter strip lengths generated significantly more tension per cross-sectional area than did the longer strips. The collagen density and distribution were similar for the control and sham bladders. The obstructed bladders had significantly increased collagen deposits between and within the smooth muscle bundles and cells.

Because the relationship between strip size and contraction were similar for field stimulation, carbachol, and potassium chloride, it is the increased density of connective tissue within and between the muscle bundles and fibers that interferes with contraction (ie, the greater the strip length, the greater the interference and the greater the contractile dysfunction). Therefore, both functional and structural alterations in the obstructed bladder participate in contractile dysfunction.