Electroacupuncture Relieves Labour Pain and Influences the Spinal Dynorphin/κ-Opioid Receptor System in Rats

Abstract

Background The dynorphin (DYN)/κ-opioid receptor (KOR) system plays a key role in the control of labour pain. Our previous clinical study reported that electroacupuncture (EA) provided intrapartum analgesia, but the underlying mechanisms of action have not been fully elucidated. Aims To observe the effect of EA on labour pain and to explore the underlying mechanisms of action in a rat model. Methods Copulation-confirmed pregnant rats (n=120) were given castor oil to induce labour. Rats remained untreated (control group, n=20) or received either meperidine (an opioid that is commonly used to treat labour pain, n=20) or EA at SP6, LI4, SP6+LI4 or SP10 (four groups, n=20 each). Labour pain was evaluated by the warm water tail-flick test. Serum DYN values were measured by ELISA. Protein and mRNA expression of prodynorphin (PDYN, the precursor protein of DYN) and KOR were analysed by Western blotting and real-time PCR, respectively. Results EA treatment at all acupuncture point combinations studied significantly relieved labour pain and increased serum DYN concentrations, to a degree similar to that achieved with meperidine. EA notably enhanced protein expression of KOR and PDYN and mRNA expression in the lumbar spinal cord but not in the cerebral cortex. The size of effect varied by EA group in the order: SP6>LI4>SP6+LI4>SP10 for all parameters measured, indicating differential effects relating to acupuncture point selection/combination. Conclusions The present study indicates that EA relieves labour pain, at least in part, by regulation of the spinal DYN/KOR system in a rat model.