Involvement of opioid receptors in inhibition of bladder overactivity induced by sacral neuromodulation in pigs: A possible action mechanism.

AIMS: To determine the role of opioid receptors in the inhibition of bladder overactivity by sacral neuromodulation (SNM) in pigs, and explore the possible mechanism of SNM.

METHODS: Both implant-driven stimulators of the S3 spinal nerve were implanted in seven pigs. Naloxone and tramadol were administered. Multiple cystometrograms were performed to determine the effects of SNM and opioid receptors on the micturition reflex by infusing normal saline (NS) or acetic acid (AA).

RESULTS: AA-induced bladder overactivity significantly reduced the bladder capacity (BC) to 29.9 ± 3.9% of the NS control level (413.1 ± 55.4 mL) (P < 0.01). SNM significantly increased the BC to 39.4 ± 5.5% of the NS control level (P < 0.03). In the absence of SNM, the cumulative dose of naloxone (0.02 and 0.2 mg/kg intravenously) did not significantly change the BC (25.1 ± 3.1% and 20.2 ± 3.1% of the NS control level, respectively) (P > 0.05). In the presence of SNM, both doses of naloxone significantly reduced the BC to 27.2 ± 3.0% and 25.1 ± 2.9% of the NS control level (P < 0.05), respectively. In the absence of SNM, tramadol did not significantly change the BC (31.5 ± 3.9% of the NS control level) (P > 0.05). In the presence of SNM, tramadol significantly increased the BC to 49.1 ± 6.1% of the NS control level (P < 0.01).

CONCLUSIONS: Opioid receptors play a role in inhibition of bladder overactivity during SNM. Combining SNM with tramadol could be a novel treatment modality for overactive bladder.