The role of
anandamide in the development of inflammatory
hyperalgesia and visceral
hyperreflexia was studied in the rat urinary bladder. Animals were given intraperitoneal
cyclophosphamide injection, which evokes painful
hemorrhagic cystitis accompanied by increased bladder reflex activity. The
vanilloid receptor 1 [transient receptor potential vanilloid 1 (TRPV1)] antagonist
capsazepine, applied onto the serosal surface of bladders, significantly reduced the
hyperreflexia. Mass spectrometric analysis revealed that
cyclophosphamide injection significantly and persistently increased the
anandamide content of bladder tissues. The increase in the
anandamide content paralleled the development of reflex hyperactivity.
Anandamide (1-100 microm), applied onto the serosal surface of naive bladders, increased the reflex activity in a concentration-dependent manner. Repeated
anandamide applications did not produce desensitization of the response. The
anandamide-evoked effect was blocked by
capsazepine or by instillation of
resiniferatoxin, the ultrapotent TRPV1 agonist, into the bladders 24 hr before the
anandamide challenge. The
cannabinoid 1 receptor antagonist
SR141716A [N-piperidino-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-
4-methylpyrazole-3-carboxamide] significantly increased the potency of
anandamide in enhancing bladder reflex activity in naive but not in
cyclophosphamide-injected animals. Application of the
fatty acid amide hydrolyze inhibitor palmitoylisopropylamine onto the serosal surface of bladders also increased the reflex activity both in naive and
cyclophosphamide-injected rats. This latter effect in naive animals was blocked by
capsazepine and by
resiniferatoxin pretreatment. Finally,
intravesical instillation of
anandamide (50 microm) increased c-fos expression in the spinal cord, which was reduced by
capsazepine or by
resiniferatoxin pretreatment. These results suggest that
anandamide, through activating TRPV1, contributes to the development of
hyperreflexia and
hyperalgesia during
cystitis.