BACKGROUND: β-endorphin is the most actively endogenous substance of cerebral endorphin. When combined with opiate receptor specially, it manifests a strong morphine-like activity and can decrease sensitivity of central nervous system to carbon dioxide so as to inhibit breath.OBJECTIVE: To observe the changes of content of plasma β -endorphin in neonates with severe asphyxia after naloxone treatment in a large dosage.DESIGN: Randomized controlled observation.SETTINGS: Department of Pediatrics, Shenzhen Shajing Peoples Hospital; Center of Pediatrics,Guangzhou Zhujiang Hospital.PARTICIPANTS: A total of 97 neonates with severe asphyxia including 57 boys and 40 girls were selected from Neonatal Intensive Care Unit, Department of Pediatrics, Shenzhen Shajing Peoples Hospital from January 2004 to November 2005. Their gestational age was (38 ±3) weeks, body mass was (3.2± 1.7) kg,and hospitalization duration was (2.8±2.3) hours. All neonates met the diagnostic criteria of with severe asphyxia and all their parents provided the confirmed consent.METHODS: All neonates were treated with inspired oxygen, sedation, stopping terror, decreasing cranial pressure, maintaining a well blood perfusion and normal level of blood glucose (about 5.0 mmol/L). After hospitalization, 0.1 mg/(kg ·d) naloxone hydrochloride (Beijing Sihuan Pharmaceutical Technology Co., Ltd.;certification: H10900021; bullet preparation; 0.4 mg/ampoule) was intravenously dribbled into neonates for 4 - 6 hours, 14 days in total. 2 mL blood was collected from radial artery in neonates at the beginning of hospitalization and at 3 days after naloxone treatment, put in aprotinin-pre-cool tube, mixed evenly, and centrifuged at hypothermia. Plasma was maintained in refrigerator at - 70 ℃. The kit was provided by Neurobiology Department of Shanghai Second Military Medical University of Chinese PLA. Concentration of plasma β -endorphin was measured by using radio-immunity assay.All data were expressed as Mean±SD and results were compared with paired t test.MAIN OUTCOME MEASURE: Concentration of plasma β -endorphin.RESULTS: All 97 neonates were involved in the final analysis. Concentration of plasma β -endorphin in neonates with severe asphyxia was lower after treatment as compared with that before treatment, and there was significant difference (t =10.31, P ＜ 0.01).CONCLUSION: Naloxone can decrease level of plasma β -endorphin in neonates with severe asphyxia.