Autonomic effects of electroacupuncture in opioid-induced constipation in male rats

The efficacy of electroacupuncture (EA) for opioid-induced constipation (OIC) has been reported; however, the mechanism has not been sufficiently studied, and the details have not been clarified. The aims of this study were to demonstrate the delay in rat colonic transit (CT) caused by loperamide, a peripheral μ-opioid receptor agonist, and to evaluate the effect of EA at ST-36 on the autonomic nervous system. To measure CT, the operation had been demonstrated for setting the cannula into the cecum to connect the proximal colon. On the fifth day after surgery, 20 metal radiopaque markers were administered to the proximal colon and visible throughout the gastrointestinal tract via soft X-ray immediately after the administration of markers up to 240 min. The OIC model was induced in rats by subcutaneous injection of loperamide twice a day for 3 days, and EA at ST-36 was performed before measurement. The delay in CT caused by loperamide was significantly improved with EA, which was abolished by atropine. CT delay was significantly accelerated by α-adrenoceptor antagonists and acetylcholinesterase inhibitors. This study showed that EA has the potential to be effective for OIC, and that the autonomic nervous system is involved in its mechanism.