Cystometric evidence that capsaicin-sensitive nerves modulate the afferent branch of micturition reflex in humans.

Intravesical instillation of capsaicin (0.1 to 10 microM) in six patients (five with hypersensitive disorders of the lower urinary tract, one with benign prostatic hyperplasia) produced a concentration-related reduction of the first desire to void, bladder capacity and pressure threshold for micturition. At a threshold concentration of one microM, capsaicin also produced a warm to burning sensation referred to the suprapubic area during the collecting phase and to the urethra during micturition. All the patients with hypersensitive disorders of the lower urinary tract reported disappearance or marked attenuation of their symptoms for a few days after capsaicin application. In three other patients with hypersensitive disorders of the lower urinary tract, intravesical instillation of capsaicin's vehicle (0.1% ethanol in saline) did not produce significant cystometric changes nor modify the symptomatology. These observations provide the first indication that capsaicin-sensitive structures (nerves?) may be present in the human urinary bladder as they have been shown to occur in various other species.