No evidence for mediation of ischemic preconditioning by alpha1-adrenergic signal transduction pathway or protein kinase C in the isolated rat heart

Summary The purpose of this study was to elucidate the role of activation of the alpha₁-adrenergic signal transduction pathway and of protein kinase C (PKC) in the mechanism of protection of functional recovery by ischemic preconditioning in the isolated perfused rat heart. After a stabilization period, nonpreconditioned and preconditioned isolated perfused rat hearts were subjected to sustained ischemia for 25 and 30 minutes of reperfusion. Preconditioning consisted of three episodes of 5 minutes of ischemia, interspersed with 5 minutes of reperfusion. The endpoint was postischemic functional recovery. The effectiveness of preconditioning in the presence of the alpha₁-adrenergic blocker prazosin, the selective PKC blockers chelerythrine and bisindolylmaleimide (BIM), and the ability of repetitive alpha₁-adrenergic activation to mimic preconditioning were compared with the appropriate nonpreconditioned and preconditioned control groups. Alpha₁-adrenergic blockade with prazosin (3×10^-7 M) during the preconditioning phase did not abolish the protective effect of preconditioning on functional recovery, and repeated intermittent alpha₁-adrenergic activation with phenylephrine in different concentrations (1×10^-8 to 3× 10^-5 M) did not mimic the protective effect of preconditioning. PKC blockade with the selective PKC inhibitors, chelerythrine (10 M) and BIM (4 M), did not abolish the protective effect of preconditioning on functional recovery is isolated perfused rat hearts when given either during the preconditioning phase or shortly before the onset of sustained ischemia. The characteristic metabolic changes of preconditioning during sustained ischemia, namely, energy sparing as manifested in reduced accumulation of lactate, were also not abolished by preconditioning in the presence of selective PKC blockers. We conclude that no evidence could be found for alpha₁-adrenergic or PKC activation in the mechanism of ischemic preconditioning in the isolated rat heart.