Activating mu-opioid receptors in the spinal cord mediates the cardioprotective effect of remote preconditioning of trauma

BACKGROUND: Remote precoditioning of trauma (RPCT) confers cardioprotective effects against myocardial ischemia/reperfusion injury, which are mediated by spinal opioid receptors. The aim of this study was to identify the roles of opioid receptor subtypes in the cardioprotective effect of RPCT and possible mechanisms. METHODS: In this study, 192 Sprague-Dawley rats were allocated to 12 groups. Except for the sham group, rats in all groups were subjected to myocardial ischemia reperfusion. Rats in the ischemia precondition (IPC) group were treated with IPC. In the RPCT groups, an abdominal incision was made 15 min before inducing ischemia. The selective delta-, kappa-, and mu-opioid receptor antagonists were administered to groups of animals receiving RPCT, respectively. Data were collected for myocardial infarct size, intercellular adhesion molecule 1 (ICAM-1), plasma cardiac troponin I (cTnI) concentrations, activation of protein kinase C epsilon (PKCe) in myocardial cell membranes, and adenosine release in the spinal cord. RESULTS: Compared with the control groups, infarct size, plasma concentrations of cTnI, and myocardial ICAM-1 expression were significantly lower, while adenosine release and PKCe activation were enhanced in the IPC and RPCT groups. Compared with the RPCT group, infarct size, plasma cTnI concentration, and myocardial ICAM-1 expression were greater and adenosine release and PKCe activation were reduced in the mu-opioid receptor antagonist plus RPCT group. CONCLUSIONS: The spinal mu-opioid receptor mediated the cardiac protective effect of RPCT. The mechanism may be enhanced by adenosine release in the spinal cord and PKCe activation in the myo-cardium, thereby inhibiting inflammation induced by ischemia/reperfusion injury.