Bladder filling in mice: an experimental in vivo model to evaluate the reservoir function of the urinary bladder in a long term study.

We report a simple, reproducible, and low-invasive in vivo method for repeated examination of bladder well properties in mice. Over a period of 21 days transurethral bladder fillings were performed every second day on the same animal. Analysis of the bladder volume at an intravesical pressure of 10 and 20 mm. Hg and at the leakage point showed no trend during the 21 day study period with regard to changes in bladder volume. The model has been applied to a group of mice treated with a single fraction bladder irradiation dose of 20 Gy. These mice were investigated repeatedly during the following year. The end point selected for data evaluation in the irradiated group of mice was a 50% decrease in bladder volume at an intravesical pressure of 20 mm. Hg relative to the control value (bladder volume before irradiation). The results clearly demonstrate a biphasic change in the bladder reservoir function, in the form of an acute, reversible change, a period of normalization and then a late irreversible damage. The latter stage is consistent with the clinically found contracted bladder. In a control group there was no significant change in bladder volume during the study period of more than 200 days. The model thus appears feasible for future studies of bladder irradiation damage.