Use of injectable fat to obstruct the urethra in rabbits

Bulking agents have been injected to correct urinary incontinence for at least 15 years. The injection seeks to increase bladder outlet resistance by partially obstructing the urethra and thereby reduce urinary leakage in patients with stress urinary incontinence. Although the implant is effective and requires a shorter in-hospital stay than more traditional procedures, no ideal implant substance has been discovered. To assess the effectiveness of injected fat as a bulking agent, we injected small volumes of perivesical fat into the bladder neck in New Zealand White (NZW) rabbits and tested the effect on the bladder. In eight rabbits, we harvested perivesical fat and partially closed the urethral lumen with an initial injection. A second injection 1 month later completely closed the urethral lumen. We injected six other rabbits with similar volumes of saline as controls. Two weeks after the second injection, we measured micturition frequency, bladder weight, response to electrical field stimulation, and response to bethanecol in each group. Fat implants were present at the injection site in each case 4 weeks after the first injection. Rabbits receiving fat implants had increased micturition frequency, increased bladder weight, and increased response to bethanecol and field stimulation. Previous studies have demonstrated that these changes are characteristic of mild outlet obstruction in rabbits. Injected fat can be made to close the urethra and create bladder outlet obstruction in rabbits. The short-term success of fat as a bulking agent in this experiment is encouraging and suggests the need for longer term studies.