Excitatory and inhibitory urinary bladder reflexes induced by stimulation of cervicovaginal capsaicin-sensitive sensory fibers in rats

We have investigated the effect of intravaginal application of capsaicin on micturition reflex in female rats. Urinary bladder contractility was measured by transurethral pressure recording at isovolumetric and subthreshold conditions in anaesthetized rats. The intravaginal application of capsaicin (15 mug/50 mul rat) induced reproducible bladder phasic contractions, without desensitization upon repeated applications, that were blocked by intravenous atropine (1 mg/kg) or hexamethonium (5 mg/kg) and prevented by removal of paracervical ganglia or systemic capsaicin pretreatment (125 mg/kg, s.c.). The inhibition of sympathetic transmission by guanethidine (30 mg/kg, s.c.) produced significant increase of the bladder reflex contractions activated by intravaginal capsaicin. Intravenous administration of the TRPV1 antagonist, capsazepine (3 mg/kg), significantly reduced the excitatory reflex response to capsaicin. Intravaginal administration of capsaicin (15 mug/50 mul), during distension-induced reflex bladder contractions, produced a transient block of reflexes, unaffected by guanethidine pretreatment. In conclusion, the stimulation of capsaicin-sensitive sensory nerve endings in the rat cervix-vagina induced a dual excitatory or inhibitory bladder response in anaesthetized female rats depending on the degree of bladder distension.