The Location Of SP, CGRP MRNA And The Expression Of NK₁ Receptor, β₁-adrenoceptor In Myocardium Following Coronary Artery Occlusion In Rats

Aim:The current study was to investigate the role of substance P(SP) in mediating the neurogenic reaction in acute myocardial ischemia(AMI) by exploring the change in NK₁ receptor andβ₁-adrenoceptor(β₁-AR) in rat heart after coronary artery occlusion(CAO),and the intervention effects of pre-treatment with ropivacaine and morphine.The expression of PPT-A mRNA,calcitonin gene related peptide(CGRP) mRNA in dorsal root ganglia(DRG),spinal cord. heart and lung were also studied.Background:Although increased evidence indicated the regulating effects of SP and CGRP on cardiovascular system,the detailed exact molecule mechanisms were not fully established. Recent studies found that the concentration of these mentioned bioactive compounds was increased in myocardium when heart plunged into acute infarction,indicating SP and CGRP were involved in pathological process of acute myocardial ischemia.Little is known about the role of neuropeptides in this effect of myocardial ischemia.Methods:The experiment was performed in three steps.In step one,adult male SD rats were randomly devided into two groups:Sham group,with the same scheme of surgery without CAO;CAO group,with the left anterior descending branch of coronary artery occluded under general anaesthesia.Then rats were killed at 3h after CAO,and the samples were collected for hybridization in situ(ISH).The expression of PPT-A mRNA,CGRP mRNA in DRG,spinal cord, heart and lung of the rats were examined,and the innervation of heart,lung,intestine and spleen was also observed using silver staining.In step two,the groups were same as in step one,but further devided respectively into three subgroups:CAO1h,3h and 6h group.Then rats were killed as scheduled at different time points, and the samples were collected.The location and protein level of NK₁ andβ₁-AR in myocardium were examined by immunohistochemistry(IHC) and Western blot analysis.In step three,the time point of highest expression of NK₁ orβ₁-AR after CAO was chosen respectively for interventional study according to the results in step two.Rats were randomly devided into four groups:Sham group,CAO group,E-R(epidural ropivacaine) group and Group E-M(epidural morphine) group.At 15 minutes before CAO,rats were pre-treated epidurally with 1%ropivacaine 120μg·kg^-1 or 3.75%morphine 60μg·kg^-1.Then rats were killed as scheduled,and the samples were collected for IHC and Western blot analysis.Results:1.PPT-A mRNA and CGRP mRNA were distributed widely but mainly in DRG and spinal cord.2.There is developed local innervational network in organ.3.In CAO3h and 6h group,NK₁ receptor in myocardium was up-regulated significantly compared with Sham group.4.The expression ofβ₁-AR was increased markedly in global heart after CAO,and the climax was observed at CAO 1h.5.In group E-R and E-M,NK₁ andβ₁-AR protein levels were decreased significantly compared with CAO group.Conclusions:1.The location of PPT-A mRNA and CGRP mRNA was similar.2.The results of silver staining implied the close relationship between neuropeptide and local innervational network.3.Excessive expression of NK₁ andβ₁-AR in heart were involved in pathophysiological changes in AMI.It may demonstrate that AMI,as a nociceptive stimulus,activated the neurogenic reactions and NK₁ might play some role in the process.During this period,the activity of sympathetic system was increasing accompanied by upregulation ofβ₁-AR.4.Thoracic epidural infusion of ropivacaine and morphine could partly inhibit the excessive expression of myocardial NK₁ andβ₁-AR induced by ischemia.Further investigation on the subject is invited.