Activation of p38 MAPK induced by a multi-cycle ischaemic preconditioning protocol is associated with attenuated p38 MAPK activity during sustained ischaemia and reperfusion

The role of p38 mitogen-activated protein kinase (MAPK) in ischaemic precon ditioning remains controversial, Since most previous studies focussed on ev ents only during sustained ischaemia, the aim of this study was to establis h the activation pattern of p38 MAPK during a multicycle preconditioning pr otocol, sustained ischaemia as well as reperfusion and to correlate these e vents with functional recovery of the isolated perfused rat heart. Isolated perfused rat hearts were preconditioned by 3 x 5 min global ischae mia followed by 25 min global ischaemia and 30 min reperfusion. Non-precond itioned hearts were subjected to 25 min global ischaemia and 30 min reperfu sion, Hearts were freeze-clamped and p38 MAPK activation in tissue lysates was assessed 631 standard Western blotting techniques using a dual phospho- p38 MAPK antibody as well as a non-radioactive IP-kinase assay. The results showed that transient dual phosphorylation and activation of p38 R MAPK oc curs during a 3 x 5 min preconditioning protocol: the activation was maxima l during the first episode, becoming progressively lower during the second and third episodes, p38 MAPK activation was significantly less during both sustained ischaemia and reperfusion in preconditioned hearts, when compared with non-preconditioned hearts. Attenuation of p38 MAPK activity during su stained ischaemia and reperfusion was associated with improved functional r ecovery. The effect of inhibition of p38 MAPK activation on cardioprotection was fur ther evaluated in adult, isolated cardiomyocytes. Administration of SE 2035 80 (1-10 muM) before and during the preconditioning protocol, had no effect on cell morphology and viability after 2 h hypoxia, compared to untreated preconditioned cardiomyocytes. When administered to non-preconditioned cell s before the onset of 2 h hypoxia, it caused a significant improvement in b oth morphology and viability. In summary, the results suggest that attenuation of the kinase activity dur ing sustained ischaemia and reperfusion may be an essential element of the preconditioning process. (C) 2001 Academic Press.