Investigation On The Antagonistic Effect And The Priliminary Mechanism Of Guiyuan On Morphine-induced Analgesic Tolerance And Hyperalgesia

activation. These intracellular cascades induced by chronic administration of opioidreceptor agonists finally facilitate the formation and development of analgesictolerance and hyperalgesia.Guiyuan is a compound tablet of traditional Chinese medicine, which isdeveloped by our research group. This compound preparation consists of themedicinal herbs extracts of Radix Ginseng, Radix Stephaniae Epigaeae, RadixAstragali. Our previous studies found that this compound preparation in the animalexperiments could effectively inhibit the behavioral sensitization of mice, theconditioned place preference (CPP) of rats, and the long-term potentiation (LTP)changes of hippocampus in rats, all of which were induced by morphine. The resultsof the following clinic trials also revealed that this compound preparation had benefitsin treating the withdrawal symptoms of morphine additional patients. Furthermore, wefound that Guiyuan exhibited an analgesic effect in the mice hot-plate and acetic acidwrithing tests. However, it’s unknown that after co-administration of morphine withGuiyuan, whether this compound preparation could enhance the morphine analgesiceffect and prevent the development of morphine-induced analgesic tolerance andhyperalgesia. Therefore, the contents of the present study are as follows:Objective:The purpose of this study is to evaluate whether Guiyuan could prevent thedevelopment of morphine-induced analgesic tolerance and hyperalgesia, and topreliminarily explore the mechanisms of its actions. We hope to develop Guiyuan intoa clinically analgesic adjuvant which can effectively antagonize the development ofmorphine-induced addiction, analgesic tolerance and hyperalgesia in pain treatment.Methods:In the present study, we adopted the mice hot-plate test to systematically evaluatethe time-effect and dose-effect relationships of the Guiyuan analgesic effect and themorphine analgesic effect after co-administration with Guiyuan. Furthermore, wesystematically evaluate the effects of Guiyuan on morphine-induced tolerance andhyperalgesia by establishing the morphine acute, chronic and established tolerancemodel in mice, and preliminary explore the mechanisms of Guiyuan onmorphine-induced analgesic tolerance and hyperalgesia by preparing the mice spinalcord sample and further detecting the nitric oxide synthase (NOS) activity and thenitric oxide (NO) content in this tissue sample. Results:1. Guiyuan tablets, a traditional Chinese medicine compound preparation,showed a weak to moderate analgesic effect in the mice hot-plate test, and its ED50value of this analgesic effect was523.5mg/kg (95%CI:362.2to756.8mg/kg) afterintragastric administration (i.g.). Guiyuan at the low dose of200mg/kg had notshown any significantly analgesic effect; but it at the moderate dose of400mg/kgpossessed the percentage of maximum possible analgesic effect (%MPAE) of52.04±12.49%60min after administration, and its effective analgesic action could last up to120min after administration; the analgesic effect of Guiyuan at the high dose of800mg/kg was78.57±10.58%60min after administration as well as the effect of5mg/kg morphine (70.94±12.98%)30min after subcutaneous injection (s.c.).2. Guiyuan, either at the moderate dose of400mg/kg with analgesic effect or atthe low dose of200mg/kg with no analgesic effect, could markedly increase theduration of morphine analgesic effect; the analgesic effect of morphine group declinedto the normal level as well as the control group just90min after administration,however, the effect of morphine combined with Guiyuan at the low and moderatedoses could last up to300min after their co-administration, and the%MPAE valuesof morphine plus Guiyuan at the two doses at this time point were51.58±12.80%and52.48±11.28%, respectively. In addition, Guiyuan at the moderate dose of400mg/kg effectively decreased the ED50value of morphine analgesic effect from4.67mg/kg (95%CI:3.87to5.64mg/kg) to0.65mg/kg (95%CI:0.40to1.06mg/kg).3. Guiyuan either at the dose of200mg/kg with no analgesic effect or at thedoses of400and800mg/kg with weak to moderate analgesic effect could effectivelyprevent the development of morphine-induced analgesic tolerance and hyperalgesia inboth morphine acute and chronic analgesic tolerance models. In the morphineestablished tolerance experiment, Guiyuan at the low dose of200mg/kg rapidlyreversed the morphine-induced established analgesic tolerance, but failed to reversethe established hyperalgesia.4. The results of detecting the levels of NOS activity and NO content in thespinal cord tissue of the morphine-induced established analgesic tolerance micerevealed that Guiyuan itself had no influence on the levels of NOS activity and NOcontent in mouse spinal cord, but could significantly inhibit the high levels of NOSactivity and NO content induced by morphine when it began to be co-administeredwith morphine from day1. And this inhibition of Guiyuan on morphine-induced high levels of NOS activity and NO content had not shown when it began to beco-administered from day4or day7.Conclusion:Guiyuan tablet, as a traditional Chinese medicine compound preparation, couldeffectively increase morphine analgesic effect through a synergism manner and couldsignificantly prolong the duration of morphine analgesic effect, which suggested thatthis compound preparation could decrease the dosage of morphine and prolong theinterval of morphine administration. At the same time, in this study, Guiyuan with thedemonstrated benefit of treating morphine development and addiction also showed itspreponderance on preventing the development of morphine-induced analgesictolerance and hyperalgesia and on reversing the morphine-induced establishedanalgesic tolerance. Therefore, it has potential to be developed into an effectivelyanalgesic adjuvant of morphine and other opioid drugs in clinical treatment of pain.