Abstract
Remote intrathecal morphine preconditioning (RMPC) induces cardioprotection via a neural pathway. Intrathecal lidocaine (LID) blocks spinal cord nerve transmission. This study examine whether LID prevents the effects of RMPC. Anesthetized, open chest, male Sprague-Dawley rats were assigned to one of seven treatment groups 3 days after intrathecal catheter placement. Rats from both RMPC and LID groups, respectively, received intrathecal morphine (3 μg/kg) and lidocaine (1%, 10 μL); morphine was administered by three cycles of 5-minute infusions interspersed with 5-minute infusion-free periods. The LID + RMPC group received the combination of LID and RMPC. Intrathecal naloxone methiodide (NM) (20 μg/kg) was administered either 15 minutes before RMPC, or 5 minutes before LID + RMPC. Ischemia and reperfusion injury were then induced by 30 minutes of left coronary artery occlusion, followed by 120 minutes of reperfusion. Infarct size, as a percentage of the area at risk (AAR), was determined by 2,3,5-triphenyltetrazolium staining. The RMPC and LID groups markedly reduced the infarct size (IS) compared with controls. LID prevented the effect of RMPC. NM had no effect on control and LID + RMPC treatments. However, NM pretreatment reversed cardioprotection of RMPC treatment. Intrathecal morphine preconditioning is ineffective in the presence of neuraxial blockade with lidocaine.