Endocannabinoids are endogenous brain ligands of cannabinoid receptors and have specific synthesizing,transporting,metabolizing ways in the body. Endocannabinoids can regulate release of some neurotransmitters such as glutamate or GABA. So elucidating the mechanism of endocannabinoids is not only helpful in understanding the mechanisms of cannabiod addicton but also useful in developing new useful drugs.

Objective To evaluate the efficacy of oxycodone mixed with dexmedetomidine for patient-controlled intravenous analgesia (PCIA) after renal transplantation.Methods Sixty American Society of Anesthesiologists physical status Ⅱ or Ⅲ patients of both sexes,aged 28-51 yr,weighing 53-76kg,scheduled for elective allografl renal transplantation under general anesthesia,were divided into 2 groups (n=30 each) using a random number table:oxycodone group (group O) and oxycodone mixed with dexmedetomidine group (group OD).PCIA was carried out at the end of surgery.PCIA solution contained oxycodone 1.0 mg/kg and tropisetron 5 mg in 100 ml of normal saline in group O and oxycodone 0.6 mg/kg,dexmedetomidine 5 μg/kg and tropisetron 5 mg in 100 ml of normal saline in group OD.PCIA pump was programmed to deliver 0.5 ml with a lockout interval of 15 min and background infusion at 2 ml/h,maintaining visual analog scale scores ≤ 4.When visual analog scale scores ＞4,oxycodone 0.05 mg/kg was intravenously injected as rescue analgesic.At 10 min before anesthesia and 4,12,24 and 48 h after operation,venous blood samples were collected for determination of plasma endothelin,blood urea nitrogen and creatinine concentrations (radio-immunity method) and epinephrine and norepinephrine concentrations in plasma (by high-performance liquid chromatography-electrochemical detection assay).The urine volume was recorded at each time point after the operation.The effective pressing times of PCIA and requirement for rescue analgesic were recorded within 48 h after operation,and the rate of rescue analgesia was calculated.The occurrence of adverse reactions such as over-sedation,nausea,vomiting,dizziness,respiratory depression and catheter-related bladder irritation symptoms was recorded within 48 h after operation.Parent's satisfaction with analgesia was assessed within 72 h after operation.Results Compared with group O,the concentrations of endothelin,blood urea nitrogen,creatinine concentrations,epinephrine and norepinephrine in plasma were significantly decreased,and the urine volume was increased at 12,24 and 48 h after operation,the rate of rescue analgesia was decreased,the effective pressing times of PCIA were reduced,the degree of parent's satisfaction with analgesia was increased,and the incidence of nausea and vomiting was decreased in group OD (P＜0.05).Conclusion Oxycodone mixed with dexmedetomidine produces better efficacy than either alone when used for PCIA after renal transplantation.