Ligand triggers of classical preconditioning and postconditioning.

The cardioprotection afforded by ischemic preconditioning (IPC) and ischemic postconditioning (PC) are receptor mediated. In this review, we will focus on the major ligand classes and receptors that contribute to IPC and PC-induced cardioprotection. Ligand classes discussed include adenosine, bradykinin, opioids, erythropoietin, adrenergics and muscarinics. The cardioprotective therapeutic window of each ligand class will also be summarized, with particular focus as to whether ligands are protective when administered at or close to the time of reperfusion. Information will primarily be directed at studies in which infarct size reduction is the gold standard to assess the efficacy of IPC and PC. Myocardial stunning is a less robust endpoint for assessing cardioprotection and the use of this endpoint is only limited to studies with human tissue where infarct size assessment is not possible. Receptor cross-talk between ligands and the common signaling pathways involved for these ligands will also be briefly discussed.