Intraprostatic capsaicin injection as a novel model for nonbacterial prostatitis and effects of botulinum toxin A.

OBJECTIVES

An animal model for nonbacterial prostatitis in rats was developed with the use of intraprostatic injection of capsaicin, an agent thought to excite C-afferent fibers and cause neurogenic inflammation. The analgesic and anti-inflammatory properties of botulinum toxin type A (BoNT-A) was tested in this model.

METHODS

Adult male Spraque-Dawley rats were injected with varying doses of capsaicin into the prostate. The nociceptive effects of capsaicin were evaluated for 30min by using a behavior approach; then the prostate was removed for histology and cyclooxygenase (COX) 2 protein concentration measurement. Evans blue (50mg/kg) was also injected intravenously to assess for plasma protein extravasation. A second set of animals were injected with up to 20U of BoNT-A into the prostates 1 wk prior to intraprostatic injection of 1000micromol/l capsaicin.

RESULTS

Capsaicin dose dependently induced modifications in pain behavior: closing of the eyes, hypolocomotion, and inflammatory changes: increase of inflammatory cell accumulation, COX2 expression, and plasma extravasation at the acute stage, but completely recovered at 1 wk. BoNT-A pretreatment dose dependently reversed pain behavior and inflammation. BoNT-A 20U significantly decreased inflammatory cell accumulation, COX2 expression, and Evans blue extraction (82.1%, 83.0%, and 50.4%, respectively), and reduced pain behavior (66.7% for eye score and 46.5% for locomotion score).

CONCLUSIONS

Intraprostatic capsaicin injection induced neurogenic prostatitis and prostatic pain, and may be a useful research model. BoNT-A produced anti-inflammatory and analgesic effects, and support clinical evaluation in prostatitis.