Polyamines (putrescine, spermidine, and spermine)play an essential role in cell growth, differentiation, andapoptosis. Protein kinase C (PKC) stimulates polyaminebiosynthesis through the induction of ornithine decarboxylase(ODC), a rate-limiting enzyme in polyaminebiosynthesis. Activation of PKC mediates ischemic preconditioningto reduce necrosis and apoptosis in intacthearts and in isolated culture cardiomyocytes. In this study,we examined whether the ODC/polyamine system isinvolved in the ischemic preconditioning signaling pathwayand whether this system interacts with PKC inpreconditioning-induced cardioprotection. Hearts werepreconditioned with three cycles of 5-min ischemia and5-min reflow, which caused an increase of ODC expressionand spermidine, spermine, and total polyamine pool levels.a-Difluoromethylornithine (DFMO) and ethylglyoxal bis(guanylhydrazone) (EGBG) inhibited the key enzymesinvolved in polyamine biosynthesis, and abolished thepreconditioning-induced reduction in infarct size andimprovement in postischemic heart contractility function.They also increased cell apoptosis extent and aggravatedmyocardium ultrastructure damage. Inhibition also attenuatedthe preconditioning-induced translocation and activationof the PKC-d,-e isoforms from the cytosol to theparticulate. Conversely, activation of PKC by phorbol 12-myristate 13-acetate (PMA) upregulated the ODC/polyaminesystem, whereas the PKC inhibitor chelerythrine(Che) downregulated the ODC/polyamine system. Thesefindings suggest that upregulation of the polyamine synthesismetabolism occurs in response to preconditioningand mediates preconditioning-induced cardioprotection.The ODC/polyamine system and PKC signals may "crosstalk" in preconditioned hearts such that inhibiting onepathway leads to a reduction in the activity of the otherpathway and vice versa.