Wang Yuemin

Anti-arrhythmic Effects of κ-Opioid Receptor and Its Changes in Ischemia and Reperfusion

BACKGROUNDnIt remains unclear whether the kappa-opioid receptor (kappa-OR) is altered during ischemia and reperfusion. Therefore, the present study was designed to investigate changes in the kappa-OR. Additionally, the anti-arrhythmic effect induced by kappa-OR stimulation was also determined during ischemia and reperfusion (I/R).nnnMETHODSnRats were randomly divided into different groups according to two experimental protocols. The anti-arrhythmic effects of U50,488H, a selective kappa-OR agonist, in an I/R model of 15-min ischemia were studied followed by 15 min of reperfusion. The content of kappa-OR mRNA and protein were measured by RT-PCR and Western blotting techniques in an I/R model of 30-min ischemia followed by 360 min of reperfusion.nnnRESULTSnLimited numbers of premature ventricular contractions (PVCs) were revealed in the control group. Administration of U50,488H in the control group had no effect on occurrence of PVCs. Incidence of arrhythmia in the I/R group was significantly increased. Treated with U50,488H in the I/R group, the incidence of arrhythmia was significantly reduced. With prior use of nor-BNI, a selective kappa-OR antagonist, the anti-arrhythmic effect of U50,488H was completely blocked. Compared with the control group, the content of kappa-OR mRNA and the density of kappa-OR protein increased significantly at 0 min, 60 min, and 180 min during reperfusion.nnnCONCLUSIONSnThe present study provides evidence for the first time that the expressions of kappa-OR mRNA and protein are upregulated in the heart of I/R rats. This alteration may produce a strengthened anti-arrhythmic effect upon kappa-OR stimulation during I/R.

e0152 Endogenous κ opioid peptide mediates the cardioprotection induced by ischaemic postconditioning

Aim Postconditioning is brief cycles of reperfusion and ischaemia during the early phase of reperfusion following a prolonged ischaemic insult. Opioids are well-known endogenous triggers of preconditioning. Because postconditioning shares the protective pathways with preconditioning, G protein–coupled receptor activation may serve as an essential mechanism that triggers protection of postconditioning. Receptor binding studies showed that κ opioid receptor (κ-OR) is a predominant opioid receptor in heart. Therefore, we determined whether endogenous agonist of κ-OR, dynorphin, triggers postconditioning, especially reduces apoptosis of I/R myocardium and to identify its underlying mechanism. Methods Besides the vehicle, the other SD rats underwent a 30u2005min left anterior descending occlusion followed by 120u2005min of reperfusion with or without a postconditioning stimulus (three cycles of 10u2005s reperfusion and 10u2005s reocclusion) initiated at the onset of reperfusion. The selective κ opioid receptor antagonist nor-binaltorphimine (Nor-BNI, 2u2005mg/kg, intravenously), administered 5u2005min before the reperfusion. The blood plasma was analysed spectrophotometrically for determination of CK and LDH levels. Myocardial apoptosis was quantitatively analysed by detection of TUNEL with an apoptosis detection kit. Six fields from the peri-infarct zone were analysed and the number of TUNEL positive cardiomyocytes was counted on 400 high power fields. Immunoreactive Dynorphin were measured by an antigen competitive ELISA. Results CK (U/L) and LDH (U/L) were significantly higher in I/R group than those in the control (3401±251 vs 689±76, 2329±216 vs 753±97, p<0.01). Postconditioning significantly reduced the release of CK and LDH from I/R myocardium (2026±268 vs 3401±251, 1543±169 vs 2329±216, p<0.01). These reduction were abolished by nor-BNI (p<0.01). Regional myocardial I/R resulted in a significant increase in cardiomyocyte apoptosis (18.7±2.5 vs 1±0.25, p<0.01). Postconditioning exerted a significant anti-apoptotic effect (10.4±1.3 vs 18.7±2.5, p<0.01). This protective effect was attenuated by pretreatment with Nor-BNI (p>0.05). Immunoreactive dynorphin content (pg/ml) in serum significantly increased after postconditioning (78.5±12 vs 37.3±6.5, p<0.01). Increased dynorphin did not reduced by κ opioid receptor antagonist Nor-BNI (p>0.05). Conclusions We find that cardiac protection and anti-apoptotic effect of postconditioning is mediated by activating κ opioid receptor. And cardiac protective and anti-apoptosis effect of postconditioning is mediated by enhanced dynorphin express in rats. Recently, clinical use of postconditioning as a treatment for cardiovascular disease has been an increasing attention, and opioid receptor triggers postconditoning, so the study of the relationship between κ opioid receptor and ischaemia reperfusion injury (IRI) may provide a new insight for the curing of IRI.