PRECONDITIONING IN OPEN HEART SURGERY

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DESCRIPTION (Investigator's abstract): "Myocardial preconditioning is believed to be the state of the art protective technique against ischemic injury. However, Preconditioning has not been applied in conjunction with open heart surgery. The mechanism of preconditioning is also not known. The proposed research will examine the mechanism of preconditioning and attempt to develop preconditioning modalities to salvage arrested heart during open heart surgery. The biochemical pathways activated by the preconditioning phenomenon and the molecular mechanism(s) of the gene expression will be studied. Hearts from the anesthetized rats and rabbits will be excised for isolated perfused heart preparation. To induce ischemic preconditioning, isolated hearts will be made globally ischemic for 5 minutes followed by 10 minutes of reperfusion. The process will be repeated four times. The hearts will then be made ischemic for 30 minutes followed by 60 minutes of reperfusion. To test our hypothesis that preconditioning occurs by tyrosine kinase receptor activation, we will use a tyrosine kinase blocker to inhibit preconditioning. To further explore whether the intracellular signaling occurs through tyrosine kinase-phospholipase D-protein kinase pathway, antiphospholipase D antibody will be used to inhibit phospholipase D activation associated with preconditioning. Activation of protein C kinase and its upstream regulators MAP kinase and MAPKAP kinase will be examined simultaneously. Biopsies and perfusate samples will be used to measure biochemical parameters which will include quantification of phospholipase C and D, diacyl glycerol, phosphatidic acid, protein kinase C, MAP kinase and MAPKAP kinase 2. The cellular injury will be monitored biochemically by measuring the LDH and CK releases. Functionally, both left ventricular systolic and diastolic functional parameters will be continuously monitored on a beat to beat basis. These will include the left ventricular stroke work, elastance, and the time constant of isovolumic relaxation. Induction for the expression of stress-related genes will be studied by Differential Display Technique. The results of this study will not only enable us to understand whether tyrosine kinase-phospholipase D-protein C kinase-MAP kinase-MAPKAP kinase 2 signaling pathway is involved in preconditioning, but also will determine whether preconditioning occurs at the molecular level by reprogramming the gene expression. The results will be useful to develop treatment modalities for preconditioning the heart during open heart surgery."