Rabbit urinary bladder blood flow changes during the initial stage of partial outlet obstruction

Purpose: The rabbit urinary bladder's early response to partial outlet obst ruction includes bladder wall remodeling with marked urothelial and fibrobl ast hyperplasia (1 day) and smooth muscle hypertrophy (3-5 days) resulting in a 4-5 fold increase in bladder mass within 7 days. In this study, we exa mined the effect of partial outlet obstruction on bladder blood flow during the initial period of rapid growth (1-7 days). Materials and Methods: Each New Zealand White rabbit was partially obstruct ed by tying a 2-0 silk ligature loosely around the vesical outlet. After 0 (unoperated), 4 hours, 1, 3, or 7 days of obstruction, 5 rabbits per group were anesthetized and the carotid and femoral arteries cannulated with poly ethylene tubing. Additional rabbits receiving sham surgeries were treated l ike obstructed animals at 4 hours and 1 day post-obstruction (5/group). Usi ng standard methods, fluorescent microspheres were infused through the righ t carotid artery. Bladder and right kidney were rapidly removed upon comple tion of sphere infusion; bladder mucosa and muscle were separated. Sphere d ensities in detrusor, mucosa, and kidney were measured by Interactive Medic al Technologies, Ltd. A section of each detrusor tissue was fixed in formal in and immunostained for smooth muscle alpha-actin. Results: Mucosal blood flow (0.20 +/- 0.03 ml./min./gm.) was similar to 4-f old greater than that of detrusor (0.05 +/- 0.01 ml./min./gm.). Sham surger y caused a significant increase in bladder blood flow at 4 hours post-obstr uction that returned to control levels by 1 day. Both mucosal and muscle bl ood flows were slightly higher in rabbit bladders obstructed for 4 hours th an in sham-operated rabbits, and substantially greater in those obstructed for 1 day: 0.68 +/- 0.13 ml./min./gm. (mucosa) and 0.26 +/- 0.04 ml./min./g m. (muscle). Blood flows returned to control values by 3 days post-obstruct ion and remained constant through 7 days. Kidney blood flow was unchanged. Although bladder weight increased 4-fold after 7 days of obstruction, the v olume fraction of smooth muscle (transverse section) remained constant at s imilar to 40%. Conclusions: Blood flow was similar to 4-fold greater in bladder mucosa tha n in muscle, which may relate to the significantly higher metabolic rate an d lower high energy phosphate concentration of mucosa than muscle. Partial outlet obstruction resulted in a significant increase in blood flow at 1 da y post-obstruction, which coincides temporally with the early cellular hype rplasia and hypertrophy of obstructed rabbit bladder. This increase in bloo d flow may be an essential factor for the initial increase in bladder mass. By three days, the blood flow per gram of tissue returned to control level s. The mechanisms relating to the changes in blood flow induced by partial outlet obstruction are currently under investigation.