title: Remote intrathecal morphine preconditioning confers cardioprotection via spinal cord nitric oxide/cyclic guanosine monophosphate/protein kinase G pathway.
abstract: BACKGROUND
  Remote intrathecal morphine preconditioning (RMPC) induces cardioprotection, but the underlying mechanisms of this effect is unknown. The aim of this study was to investigate the role of spinal cord nitric oxide/cyclic guanosine monophosphate/protein kinase G (NO/cGMP/PKG) signal pathway in the cardioprotection of RMPC in rats.
  
  
  METHODS
  Anesthetized, open chest, male Sprague-Dawley rats were assigned to one of eight treatment groups 3 d after intrathecal catheter placement. Before ischemia and reperfusion, RMPC received intrathecal morphine (3 μg/kg) by three cycles of 5-min infusions interspersed with 5-min infusion free periods. Intrathecally administrated a nonspecific nitric oxide synthase (NOS) inhibitor Nω-Nitro-L-arginine methyl ester (30 nmol), a specific guanylate cyclase inhibitor oxadiazolo [4,3-a] quinoxalin-1-one (11 nmol) and PKG inhibitor KT-5823 (20 pmol) 10 min before RMPC was used to evaluate the role of NO/cGMP/PKG of spinal cord. Ischemia and reperfusion injury were then induced by 30 min of left coronary artery occlusion, followed by 120 min of reperfusion. Infarct size, as a percentage of the area at risk, was determined by 2,3,5-triphenyltetrazolium staining. The content of cyclic guanosine monophosphate in the thoracic spinal cord was determined by radioimmunity protocol; the contents of nitric oxide and activity of NOS in the thoracic spinal cord were determined by nitrate reductase reduction and colorimetric methods; the expression of neuronal NOS (nNOS) and PKG in the thoracic spinal cord were determined by immunohistochemical and Western blotting method; the expression of nNOS messenger RNA was determined by reverse transcription-polymerase chain reaction method.
  
  
  RESULTS
  RMPC group markedly reduced the infarct size compared with the control group. However, the cardioprotection of RMPC could be abolished by pretreatment with Nω-Nitro-L-arginine methyl ester, Oxadiazolo [4,3-a] quinoxalin-1-one, and KT-5823. RMPC enhanced nitric oxide , NOS, and cyclic guanosine monophosphate levels in the spinal cord. Meanwhile, RMPC increased PKG and nNOS protein or messenger RNA expression in the spinal cord.
  
  
  CONCLUSIONS
  Spinal cord NO/cGMP/PKG signaling pathway mediates RMPC-induced cardioprotective effect.
authors.affiliation: Department of Anesthesiology, Second Affiliated Hospital of Anhui Medical University, Hefei, China; Department of Anesthesiology, Third Affiliated Hospital of Anhui Medical University, Hefei, China.
authors.forename: Yao
authors.initials: Y
authors.lastname: Lu
authors.affiliation: Department of Anesthesiology, Second Affiliated Hospital of Anhui Medical University, Hefei, China.
authors.forename: Jun
authors.initials: J
authors.lastname: Hu
authors.affiliation: Department of Anesthesiology, Second Affiliated Hospital of Anhui Medical University, Hefei, China. Electronic address: zhangye_hassan@126.com.
authors.forename: Ye
authors.initials: Y
authors.lastname: Zhang
authors.affiliation: Department of Anesthesiology, Third Affiliated Hospital of Anhui Medical University, Hefei, China.
authors.forename: Chun Shan
authors.initials: CS
authors.lastname: Dong
authors.affiliation: Department of Anesthesiology, University of Hong Kong, Hong Kong SAR, China.
authors.forename: Gordon Tin Chun
authors.initials: GT
authors.lastname: Wong
mesh_terms: D000701:Analgesics, Opioid / Q000494:pharmacology; D000818:Animals; D002316:Cardiotonic Agents / Q000494:pharmacology*; D006152:Cyclic GMP / Q000378:metabolism; D017869:Cyclic GMP-Dependent Protein Kinases / Q000378:metabolism; D006439:Hemodynamics / Q000187:drug effects / Q000502:physiology; D007278:Injections, Spinal; D019157:Ischemic Preconditioning, Myocardial / Q000379:methods*; D008297:Male; D009020:Morphine / Q000494:pharmacology*; D009203:Myocardial Infarction / Q000188:drug therapy / Q000378:metabolism / Q000503:physiopathology; D015428:Myocardial Reperfusion Injury / Q000188:drug therapy* / Q000378:metabolism / Q000503:physiopathology; D009569:Nitric Oxide / Q000378:metabolism; D052247:Nitric Oxide Synthase Type II / Q000235:genetics / Q000378:metabolism; D017207:Rats, Sprague-Dawley; D015398:Signal Transduction / Q000187:drug effects* / Q000502:physiology; D013116:Spinal Cord / Q000187:drug effects / Q000201:enzymology
chemical_list: D000701:Analgesics, Opioid; D002316:Cardiotonic Agents; D009569:Nitric Oxide; D009020:Morphine; D052247:Nitric Oxide Synthase Type II; C496318:Nos2 protein, rat; D017869:Cyclic GMP-Dependent Protein Kinases; D006152:Cyclic GMP
keywords: Morphine; Myocardial reperfusion injury; Nitric oxide; Remote preconditioning; Spinal cord