ROLE OF LIPOXYGENASE METABOLITES IN ISCHEMIC PRECONDITIONING

Preconditioning with brief intermittent periods of ischemia before a sustained period of ischemia has been shown to reduce infarct size and improve recovery of function in rat hearts. The mediators of this protective response are unknown in rats. We tested the hypothesis that a lipoxygenase metabolite might be involved in preconditioning, since lipoxygenase metabolites such as 12-hydroperoxyeicosatetraenaic acid have been shown to increase K+ channel activity and to decrease Ca2+ channel activity, which could have a protective effect on ischemic injury. In support of this hypothesis, we report that the lipoxygenase inhibitors nordihydroguaiaretic acid (NDGA, 5 mu mol/L) and eicosatetraynoic acid (7 mu mol/L) added just before and during preconditioning blocked the protective effects of preconditioning on recovery of function during reflow after 30 minutes of global ischemia. In addition, these lipoxygenase inhibitors partially blocked the ability of preconditioning to attenuate the rise in cytosolic free calcium during sustained ischemia. We also investigated the effects of preconditioning on eicosanoid metabolism by using high-performance liquid chromatography and found that 12-hydroxyeicosatetraenoic acid (12-HETE), the stable product of the lipoxygenase pathway, was made during the preconditioning protocol and that 12-HETE accumulation was blocked by NDGA. Thus, there is a correlation between functional recovery after ischemia and stimulation of the lipoxygenase pathway of arachidonic acid metabolism before the sustained period of ischemia; inhibition of the lipoxygenase pathway eliminates the protective effect of preconditioning on recovery of function after ischemia.