Effect of electroacupuncture on pain threshold and expression of pain-related factors cyclooxygenase-2, prostaglandin E2 and β-endorphin in rats with chronic pelvic pain syndrome

Abstract

To explore the possible mechanism of electroacupuncture (EA) underlying improvement of chronic pelvic pain syndrome (CPPS). Fifty SD rats were randomly divided into control, model, sham operation, EA and sham EA groups (n=10 rats in each group). The CPPS model was established by injecting complete Freund's adjuvant (CFA, 50 μL) into the ventral lobes of the prostate. EA (2 Hz/100 Hz) was applied to "Guanyuan"(CV4), "Zhongji"(CV3), "Sanyinjiao" (SP6) and "Huiyang"(BL35) once daily for 40 min, 5 days a week for 4 weeks, while rats in the sham EA group were treated with the same acupoints but without electrical stimulation. Mechanical pain threshold (MPT) and heat pain threshold (HPT) were measured before and after intervention. The body weight and prostate weight were measured and prostate index was calculated. Histopathological changes of prostate tissue were observed by HE staining. The levels of cycloxygenase-2 (COX-2), prostaglandin E2 (PGE2) and β-endorphin (β-EP) in prostate tissue were detected by ELISA. Compared with the control and sham operation groups, the MPT and HPT were significantly lower (P<0.01), and the prostate weight, prostate index, the contents of PGE2 and COX-2 were significantly increased (P<0.01), while the content of β-EP was significantly decreased (P<0.01) in the model group. Compared with the model group, the MPT and HPT were significantly increased (P<0.01) after 3 and 4 courses of treatment, and the prostate weight, prostate index, the contents of PGE2 and COX-2 were significantly decreased (P<0.01), while the content of β-EP was significantly increased (P<0.01) in the EA group, rather than in the sham EA group (P>0.05). EA can effectively relieve pain in CPPS rats, which may be related to its functions in down-regulating COX-2 and PGE2, and up-regulating β-EP.