OBJECTIVES
To investigate the effects of reactive oxygen species (ROS) on the micturition reflex in vivo, especially in bladder afferent signalling in rats, as several pathophysiological conditions in the urinary bladder (e.g. ischaemia/reperfusion and inflammation) are characterized by the formation of ROS.
MATERIALS AND METHODS
Adult female Sprague‐Dawley rats under urethane anaesthesia (normal or pretreated with 125 mg/kg capsaicin, subcutaneously, 4 days before) were assessed by continuous cystometrography (CMG) with or without the intravesical administration of H2O2 (0.003–3%) to stimulate ROS damage. To investigate the mechanism of H2O2, catalase (a H2O2 scavenger) was applied intravesically (2000 IU/mL), or rats were given intravenous injections with superoxide dismutase (SOD, 20 000 IU/kg, a superoxide anion scavenger), dimethylthiourea (DMTU, 100 mg/kg, a hydroxyl radical scavenger), deferoxamine (20 mg/kg, an iron‐chelator that prevents the formation of hydroxyl radical), indomethacin (3 mg/kg, a cyclooxygenase inhibitor) or ketoprofen (1 mg/kg, a cyclooxygenase inhibitor) just before or during the intravesical administration of H2O2. Prostaglandin (PG) levels (PGE2 and 6‐keto‐PGF1α) were measured in the bladder of rats treated with intravesical 0.3% H2O2 for 30 min with or without indomethacin.
RESULTS
Intravesical administration of H2O2 induced detrusor overactivity, as shown by a reduction in the mean (sem) intercontraction interval (ICI), in a dose‐dependent manner in normal rats (0.3% H2O2, P < 0.01, 36.2 (4.7)% of the control ICI). H2O2‐induced detrusor overactivity was almost abolished by catalase and significantly suppressed by DMTU, deferoxamine, capsaicin pretreatment, indomethacin or ketoprofen but not by SOD. The level of PGs was significantly increased by H2O2 instillation, and indomethacin significantly inhibited the increase in PGs.
CONCLUSION
These results indicate that oxidative stress induced by H2O2 activates capsaicin‐sensitive C‐fibre afferent pathways, at least in part, mediated via stimulation of the cyclooxygenase pathway, thereby inducing detrusor overactivity. Thus, rats treated with intravesical H2O2 appear to be a suitable model for the study of detrusor overactivity.
