Effect of timing of diuresis on response of rat bladder to outlet obstruction.

Objectives: To determine whether results similar to a previous study, in which sucrose-induced diuresis started before creating partial outlet obstruction resulted in protection of bladder contractile function in obstructed animals, would be obtained if diuresis were begun after creation of partial outlet obstruction.

Methods: Thirty-six rats were separated into six groups of 6 rats each: group 1, control; group 2, diuresis; group 3, obstructed; group 4, obstructed immediately after diuresis; group 5, obstructed with diuresis beginning 10 days after obstruction; and group 6, obstructed before diuresis. Diuresis was induced by feeding 5% sucrose instead of water. After 3 weeks of obstruction, all bladders were excised, cut into longitudinal strips, and mounted in isolated muscle baths for physiologic study.

Results: Sucrose-induced diuresis resulted in a statistically significant increase in bladder mass and a mild increase in smooth muscle contractility compared with the control water-fed group. Obstruction resulted in a fourfold increase in bladder weight and substantial decreases in the responses to all forms of stimulation. The bladder weights of the obstruction plus diuresed groups were all similar to the diuresis-alone group and significantly lower than those of the obstructed group. All diuresed groups showed protection of the contractile responses compared with the obstruction-alone group. Unexpectedly, the group that began diuresis 1 day after obstruction showed the strongest protection.

Conclusions: Diuresis significantly reduced the increase in bladder mass induced by obstruction and also reduced the level of contractile dysfunction. Diuresis begun 1 day after obstruction resulted in the greatest level of protection.