The Role Of Dynorphin In IPC-induced Protection Against I/R Injury

Endogenous opiod peptides (EOPs) and opiod receptors are widespreadly exist in diverse systems. Opiod peptides were thought one of central nerve peptides or one of neurotransmitter and only work for central nervous system ever since a long time ago; For twenty years, researching finds that the cells in the heart are capable of producing EOPs, which adjust self function by autocrine or paracrine, and the effect of opiod peptides mediated by corresponding receptors. Three subtypes,μ,δandκ, of opiod receptors exist in the heart, in which theκsubtype is dominant. Dynorphin is the endogenic ligand ofκopiod receptor.Ischemic preconditioning (IPC) protects the heart against subsequent sustained ischemia reperfusion (I/R). It was already discovered that many endogenously released agents have been implicated in the cardioprotective response. Activation ofκopiod receptor were found to down-regulate the contractile function of the heart and relax blood vessel. Opiod receptors can be in involved in pathology process of arrhythmia and myocardial ischemia. So in the present study, we investigated whetherκopiod receptor activation directly protects I/R heart and what role dynorphin plays in IPC heart.1,Objectives:(1) To observe the effects of IPC on dynorphin content of blood plasm and mRNA of ventricular myocytes in rat。(2) To investigate the effects of activation ofκopiod receptor on the I/R injury in rat ventricular myocytes.(3) To study the effects of blockade ofκopiod receptor on the protecting contribution of IPC in rat ventricular myocytes.2,Methods:(1) IPC model preparative method:Left anterior descending coronary artery(LAD) was occluded for 5 min followed by 5 min reperfusion, which was repeated three times.(2) I/R model preparative method:Left anterior descending coronary artery ( LAD ) was occluded for 45 min followed by 120 min reperfusion.(3) The physiological experimental technique was used to gather the rat blood and collect indexes of hemodynamics in rat.(4) The RT-PCR technique was used to investigate the changing of dynorphin mRNA in rat.(5) The RIA (radioimmunoassay) was used to determine the dynorphin content of blood plasma.(6) The dual staining was used to investigate myocardial infarction size.3,Main results:(1) IPC group (sampling after ischemia for 5 min, reperfusion for 5 min, 3 circles) increased the level of dynorphin content of blood plasm in rat (P<0.05, compared with 30 min sham group);IPC group increased the level of dynorphin content of blood plasm in rat (P<0.05, compared with con group).(2) The mRNA level of IPC group were not different from the 30 min sham group and control group (P>0.05).(3) Myocardial infarction size significantly decreased with administration of U50488H (1.5 mg/kg) in rats (P<0.01, compared with I/R group), the effect of U50488H was abolished by Nor-BNI; In comparison with control group, the contents of CK, LDH in plasma of rats in I/R group were increased. With the administration of U50488H before I/R, the contents of CK, LDH in plasma of rats in U50488H+I/R group were significantly decreased (P<0.01).(4) LVSP,±dp/dt_max significantly decreased with administration of Nor-BNI (2 mg/kg) at ischemia 10 min, ischemia 30 min, reperfusion 30 min (timing from ischemia 30 min beginning) in rats(P<0.05, compared with IPC+I/R group). 4,Conclusions:(1) The study shows that IPC promote releasing of dynorphin, and increases the level of dynorphin content of blood plasm in rat.(2) Activation ofκopiod receptor directly protects I/R heart.(3) Blockade ofκopiod receptor blunts the protective effects of IPC on the recovery of function.