Ischemia is a potent stimulus of angiogenesis, which is a known prerequisite for neoplastic proliferation and likely plays a similarly significant role in permitting benign tissue hypertrophy ([2,3]) The purpose of this study was to investigate the neovascular changes that occur in rat bladder following partial infravesical obstruction.
Methods: Adult female rats were anesthetized and surgically opened to expose the bladder and proximal urethra. A (3 \mathrm{Fr}) catheter was placed per urethra, and the catheterized proximal urethra was ligated with a 4-0 silk suture to create a fixed (1 \mathrm{~mm}) internal diameter partial obstruction. Rats were sacrificed at 4,7 and 21 days. Their bladders were weighed and frozen in liquid nitrogen. Histological sections were immunostained for the endothelial cell marker Factor VIII (vWF). Positively staining non-contiguous clusters of cells were counted in the submucosa and muscle wall areas for each bladder. Longitudinal and horizontal dimensions of bladder wall, submucosa and luminal surfaces were measured for surface area calculation. Microvessel density is reported as number of vessels per calculated square millimeter surface area.
Results: Partial infravesical obstruction resulted in an average increase in bladder mass of (298 %) and (598 %) at 7 and 21 days respectively. The absolute number of microvessels in both submucosa and muscle layers increased in early obstruction (4 - 7 days), but in both cases retumed to normal levels after three weeks (Figures 1 and 2). Microvessel density in the submucosa of partially obstructed rat bladders decreased in the initial post-obstructive stage before rebounding to near-normal levels after three weeks (Figure 1). In contrast, microvessel density in the muscle wall of obstructed rat bladders did not return to normal levels, but rather steadily declined over time (Figure 2 ).