Molecular Mechanisms Of Electroacupuncture On Mechanical Hyperalgesia In A Rat Model Of Chronic Pancreatitis

[Objective]Pain is one of the most often clinical symptoms in patients with chronic pancreatitis (CP).The mechanisms underlying the development of the pain remain unknown and current effective treatment options are very limited. The aim of present study was to investigate the involvement of endogenous H2S signaling in painful CP in rats and the therapeutic effect and mechanism of electroacupuncture.[Methods]Behavioral test:CP was induced in adult male SD rats by intraductal injection of trinitro-benzene-sulfonic acid (TNBS) or solvent for CON rats. In the time course study,the belly areas of rats by von Frey filaments(VFF) before TNBS injection and once weekly up to5weeks after induction of CP. Administration of PPG (DL-Propargylglycine,a CSE inhibitor) or treatment with electroacupuncture was applied to these rats4weeks after TNBS injection.Morphology:Four weeks after TNBS or solvent injection and treat with electroacupuncture, rats were euthanized and the pancreas was removed and fixed in10%formalin. Sections from paraffin-embedded specimens were stained with H&E to observe the pathological changes.Molecular biological study:Western blotting was employed to investigate expression of cystathionine-γ-lyase (CSE) in pancrease, cystathionine-β-synthase (CBS) and transient receptor potential vanilloid1(TRPV1) subunit in pancreas dorsal root ganglions (DRG, T9-13) relevance to pancreas.[Results]Behavioral test:(1)Mean response frequencies of TNBS treated rats were significantly increase at every time point tested up to5weeks when compared with control group (P<0.01).(2)Administration with CSE inhibitor PPG (100mg/kg body weight, ip) significantly decreased the mechanical hyperalgesia in rats injected with TNBS (P<0.05).(3)Treatment with electroacupuncture at ST36for30min daily for consecutive7days to these rats significantly decreased the mechanical hyperalgesia. The EA effect lasted for3days (P<0.01).Pancreatic histology:(1)The chronic inflammatory infiltrates, segmental gland atrophy, periductular and intralobular fibrosis, and large regions of acinar loss were observed in rats5weeks post TNBS inejction.(2)After EA treatment at ST36for30min daily for consecutive7days to these rats, the chronic inflammatory infiltrates, segmental gland atrophy, periductular and intralobular fibrosis, and acinar loss were significantly decreased when compared with sham EA treatment.Molecularbiological study:(1)The expression of CSE in the pancrease from rats4weeks after the induction of chronic pancreatitis was dramatically enhanced when compared with controls; meanwhile, expression of CBS and TRPV1in pancreas related DRGs (T9-13) were greatly upregulated compared with CON group (P<0.05).(2)EA treatment reversed the upregulation of CBS and TRPV1expression in the T9-13DRGs comparing with sham EA (P<0.01).[Conclusions]In summary, we showed that involvement of endogenous H2S signaling in painful chronic pancreatitis in rats and the electroacupuncture reduced mechanical hypersensitivity in rats with CP, which is in large part, mediated by reduction of express of CBS and TRPV1in pancreas related DRGs (T9-13), thus identifying a potential target for treatment of chronic pain in patients with CP.