Effects of capsaicin on detrusor contractility of rats: an in vivo and isolated whole bladder study.

Capsaicin has been proven to deplete neuropeptides in sensory afferent nerve terminals, causing initial excitatory and final inhibitory effects on the urinary bladder in rats and humans. In order to investigate the effect of capsaicin on detrusor contractility, an in vivo and in vitro whole bladder study was undertaken in 32 adult rats with an intact neuraxis. With intravesical application of capsaicin solution, an increased inhibitory effect of detrusor contractility was observed while the concentration of capsaicin increased. At the concentration of 1,000 microM, all rat bladders showed urinary retention in vivo. While the bladders were mounted in the baths for in vitro study, detrusor contractility was significantly affected in bladders pretreated with 1,000 microM capsaicin. Substance P-induced detrusor contraction was not affected by the presence of high concentrations of capsaicin. The presence of exogenous substance P did not improve detrusor contractility in capsaicin-pretreated bladders. The results of this study reveal that capsaicin-sensitive primary afferents have an important role in modulating reflex micturition and detrusor contractility. Depletion of neuropeptides by topical capsaicin administration at high concentrations can inhibit detrusor contractility and results in urinary retention in rats with intact neuraxis.