The Expression Of EM-2 In Myocardium, Dorsal Root Ganglion, Spinal Cord And Intestine Evoked By Coronary Artery Occlusion And Its Intervention In Rats

Objective:The purpose of this study was to explore the possible roles of endomorphin-2(EM-2)in the neurogenic mechanisms of myocardial injury induced by coronary artey occlusion,the potential mechanisms of acute local myocardial ischemia provoking globle injuries of the heart.Accordingly the surveys were made about the temporal and spatial expressions of EM-2 in myocardiums,dorsal root ganglion(DRG),spinal cord and intestine of rats after the coronary artery occlusion.Effects of pre-treatment with morphine and esmolol on the expression of EM-2 were investigated.Methods:The experiment was carried out in three steps.In step one,adult male SD rats,weighing 270-300g were randomly devided into three groups:Control group(group C),the samples were harvested from normal healthy rats directly after anaesthesia;Sham group(group S).with the same scheme of surgery with non-CAO; Coronary artery occlusion group(group CAO).Then group S and group CAO were derided into four subgroups which were observed at 0.5h,1h,3h,6h.Then the samples were excised as scheduled and processed for EM-2 immunohistochemistry(IHC).The observations were made about the temporal and spatial expressions of EM-2 in myocardiums,DRG,spinal cord and intestine of the rats after the coronary artery occlusion.In step two of the experiment,the time point of highest expression of EM-2 after CAO was chosen respectively for interventional study according to the results of step one experiment. Adult male SD rats were randomly devided into five groups:Group C(Control group);Group S (Sham group);Group CAO(Coronary artery occlusion group);Group M(Morphine group); Group E(Esmolol group).Rats were pre-treated with 1.25mg.kg^-1of Morphine in group M; 3.0mg.kg^-1of Esmolol in group E through caudal vein 15 minutes before CAO.Then rats were killed as scheduled,and the samples were collected in order to perform in immunohistochemistry (IHC)and ELISA.In step three of the experiment,Adult male SD rats were randomly devided into five groups: Group C(Control group);Group S(Sham group);Group CAO(Coronary artery occlusion group);Group M(Morphine group);Group R(Ropivacaine group).Rats were pre-treated with 15μg of morphine in group M;30μl of 1%Ropivacaine in group R through epidural space 15 minutes before CAO.Then rats were killed as scheduled,and the samples were collected in order to perform in immunohistochemistry(IHC)and ELISA. Results:(1)The expression of EM-2 in myocardium,DRG,spinal cord and intestine increased significantly after CAO as compared with the baseline in the control group(p＜0.05),and peaked at CAO3h.There was no significant difference in expression of EM-2 between ischemic myocardium and non-ischemic myocardium after CAO.EM-2 in dorsal spinal cord increased significantly compared with EM-2 in ventral spinal cord.(2)The expression of EM-2 decreased significantly in Group M and Group E comparing with Group CAO.(3)The expression of EM-2 decreased significantly in Group M and Group R comparing with Group CAO.Conclusions:(1)Coronary artery occlusion can provoke a significant increase of EM-2 in myocardium,DRG.spinal cord and intestine of rats.It demonstrates that acute myocardial ischemia,as a nociceptive stimulus,may activate the neurogenic reactions in body and EM-2 might play an important role in the whole process while the neurogenic mechanisms may contribute to the developments of myocardial injury.(2)Morphine and esmolol could attenuate the expressions of EM-2 in myocardium.DRG,spinal cord and intestine after CAO.It may imply that mechanisms of opioid,adrenergic receptors are involved in the reception of nociceptive stimulus,transfering and modulation of nociceptive information,and suppress the activation of the neurogenic mechanism induced by nociceptive stimulus.Morphine and esmolol depress the reception and transfering of nociceptive stimulus:suppress the activation of the neurogenic mechanism induced by nociceptive stimulus through different mechnisms.(3) Epidural block with Morphine and Ropivacaine could block up the transmission of nociceptive information,suppress the activation of the neurogcnic mechanism.Further investigation on the subject is urgent and worthful.