Importance of PKC and tyrosine kinase in single or multiple cycles of preconditioning in rat hearts

Both tyrosine kinase (TK) and protein kinase C (PKC) inhibitors have been s hown individually to completely abolish the cardioprotective effects of isc hemic preconditioning (IPC) in rabbits; however, blockade of both enzymes i s necessary to totally abolish IPC in pigs. Recently, we have shown that TK inhibition partially attenuates the cardioprotective effect of IPC in inta ct rat hearts. Therefore, the present study was designed to test the hypoth esis that inhibition of both TK and PKC is necessary to completely abolish IPC in the intact rat and that this effect is dependent on the intensity of the preconditioning stimulus. All animals were subjected to 30 min of coro nary artery occlusion and 2 h of reperfusion. In series I, multiple-cycle-i nduced IPC was produced via three 5-min occlusions interspersed with 5 min of reperfusion (3 x 5 IPC). Genistein (5 mg/kg), a TK inhibitor infused 30 min before IPC, and chelerythrine chloride (5 mg/kg), a PKC inhibitor infus ed 5 min before the prolonged ischemic insult, were administered alone or i n combination in the absence or presence of 3 x 5 IPC. 3 x 5 TPC produced a marked reduction in infarct size as a percentage of area at risk compared with control (8.0 +/- 0.8 vs. 56.1 +/- 0.8%). The effects of 3 x 5 IPC were partially blocked by pretreatment with genistein (34.0 +/- 2.0%) or cheler ythrine (26.4 +/- 2.8%) alone; however, combined administration of genistei n and chelerythrine completely abolished the effects of 3 x 5 IPC (50.7 +/- 3.6%). In series 2, single-cycle TPC was elicited by one 5-min occlusion f ollowed by 10 min of reperfusion (1 x 5 IPC). Compared with control, 1 x 5 IPC also significantly reduced infarct size (15.4 +/- 3.0%). Genistein or c helerythrine administered alone completely abolished 1 x 5 IPC-induced card ioprotection. These results suggest that the efficacy of TK and PKC inhibit ion to block IPC depends on the intensity of the preconditioning stimulus a nd that these kinases may work through parallel pathways.