鞘内注射吗啡预处理激活大鼠δ、κ、μ受体致心肌保护

背景鞘内注射小剂量吗啡可产生与静脉注射吗啡相似的心肌保护作用，但鞘内注射吗啡预处理（IT—MPC）与缺血预处理（IPC）作用强度的差别还未知，IT-MPC是否由阿片类受体所介导也未阐明。因此，本实验比较IT—MPC与IPC作用强度差别并探讨阿片类受体的作用。方法80只SD大鼠麻醉后开胸，成功置入鞘内导管后随机分为13组（n=6—7）。IPC组接受3次5分钟缺血-5分钟再灌注的心肌IPC（阻闭左冠状动脉），随之给予30分钟缺血-2小时再灌注诱导心肌缺血再灌注（IR）损伤。IT-MPC组按剂量不同分为4个亚组（分别是0．03、0．3、3及30μg／kg），以3次5分钟注射-5分钟间停的模式平均注入鞘内，随之诱导IR损伤。静脉注射吗啡预处理组（IV-MPC）组经静脉给予吗啡300μg／kg，对照组鞘内给予10μl生理盐水。受体阻滞剂组选择在IT—MPC（3μg/kg）前分别给予选择性δ、κ、μ受体阻滞剂NTD、nor-BNI及CTOP，以评价阿片类受体亚型的作用。通过2，3，5-tripheny ltetrazolium染色，计算心肌梗死面积（IS），即梗死心肌占缺血危险区（AAR）的百分比。结果与对照组相比，鞘内注射0．3～30μg／kg吗啡降低心肌IS，3组IS／AAR分别为33％±10％（0．3μg／kg）、29％±10％（3μg／kg）、29％±16％（30μg/kg），对照组为53％±8％（P〈0．01）。IT-MPC降低心肌IS／AAR程度与IV-MPC（33％±6％，P=0．84）及IPC（22％±4％，P=0．41）相近。注射选择性受体阻滞剂后，由IT-MPC（3μg/kg）产生的心肌预处理效果降低（NTD＋IT-MPC，50％±9％：nor-BNI＋IT-MPc，43％±6％；CTOP＋IT—MPC，53％±9％；与对照组相比，P=0．14）。结论IT—MPC产生与IPC及IV—MPC相近的心肌保护作用，其机制涉及到δ、κ、μ受体。

BACKGROUND： Small doses of intrathecal morphine provide cardioprotection similar to that conferred by IV morphine. However, the extent of intrathecal morphine preconditioning （IT-MPC） relative to that resulting from ischemic preconditioning （IPC） is unknown. Further, it is uncertain whether IT-MPC is mediated by opioid receptor dependent pathways. In this study, we compared the extent of cardioprotection conferred by IT-MPC with IPC and investigated the role of opioid receptors in this effect. METHODS： Eighty anesthetized, open-chest, male Sprague-Dawley rats were assigned to 1 of 13 groups （n = 6 - 7） after successful intrathecal catheter placement. Rats in the IPC group were subjected to three 5-min cycles of myocardial ischemia （induced by occlusion of the left main coronary artery） interspersed with 5 min of reperfusion. After IPC, myocardial ischemia and reperfusion injury was induced by 30 min of left main coronary artery occlusion followed by 2 h of reperfusion. In the IT-MPC groups, the rats were given 3 consecutive 5 min intrathecal morphine infusions （0.03, 0.3, 3.0, or 30.0 μg/kg, respectively） interspersed with 5 min infusion-flee periods, before myocardial ischemia reperfusion injury. In 2 other groups either 300 μg/kg of IV morphine or 10 μl of intrathecal normal saline were given. The selective delta, kappa, and mu opioid receptor antagonists naltrindole, nor-binaltorphimine, and D-Phe-Cys-Tyr-D-Trp-Orn-Thr-Pen-Thr-NH2 （CTOP）, respectively, were given to groups of animals receiving IT-MPC to evaluate the relative role of the specific opioid receptor subtypes in IT-MPC preconditioning. Myocardial infarct size （IS）, as a percentage of the area at risk （AAR）, was determined by 2, 3, 5-triphenyltetrazolium staining. RESULTS： Intrathecal morphine 0.3 to 30 μg/kg reduced myocardial IS compared with intrathecal normal saline control animals. The IS/AAR were 33% ±10% （0.3 μg/kg）, 29% ± 10% （3 μg/kg） and 29% ± 16% （30 μg/kg）, versus 53% ± 8% for the control group （P 〈 0.01）. The reduction in IS/AAR with IT-MPC was similar to that produced by IV morphine （33%± 6%, P = 0. 84） and IPC （22% ± 4%, P = 0. 41 ）. Myocardial preconditioning due to IT-MPC was attenuated by co-administration of any one of the opioid receptor antagonists （IT-MPC ＋ naltrindole 50%± 9%, IT-MPC ＋nor binaltorphimine 43% ± 6%, IT-MPC ＋ CTOP 53% ±9%, P = 0. 14）. CONCLUSIONS： IT-MPC produced comparable cardioprotection to myocardial IPC and IV morphine. Myocardial preconditioning from intrathecal morphine seems to involve delta, kappa, and mu opioid receptors.