Objective To study the effects of naloxone on
β-endorphin (β-EP) in plasma and on
myocardial ultrastructure during myocardial
ischemia-reperfusion (I/R) injury in rabbits.Methods The
myocardial ischemia models and myocardial ischemia -reperfusion injury models in rabbits,by ligating the left anterior descending branch of coronary artery,were used to investigate the changes of β-EP and ET-1 in plasma during I/R injury, and after treatment with naloxone, an antagonist of opiate receptor. 20 New Zealand rabbits were randomly assigned to 2 groups (each 10 rabbits in naloxone treatment and ischemia-reperfusion group). The bloods were taken at different times in each group. The concentrations of β-EP and ET-1 were detected with radioimmunology method.The changes of myocardial ultrastructure in samples of myocardial ischemia,were observed through electron microscope.Rseults The levels of β-EP were significantly improved after I/R injury compared with those before ischemia (P<0.05 or P<0.01), but in the naloxone treatment group the levels of β-EP showed no significant change in any time (P>0.05). For ischemia-reperfusion group, most of cardiac muscles were in the contracting state, the myofibril dissolved and broke locally. The edema was found on the circumference of nucleus. For naloxone treatment group, the structure of myofibril was clear and its arrangement was in good order, and no obvious breakage was found. The contracting of myofibril, the edema of mitochondria and kytoplasm were moderating. Conclusion Naloxone may effectively control the levels of β-EP and the synthesis and secreting of ET-1 after myocardial ischemia and during I/R injury;and reduce the injury to the myocardial ultrastructure and decrease the injury to blood vessel and myocardium.