Modulation of the cardioprotective effect of ischemic preconditioning in hyperlipidaemic rat heart.

Ischemic preconditioning (IPC) produces cardioprotection by phosphorylation of glycogen synthaes kinase-3beta (GSK-3beta) that inhibits the opening of mitochondrial permeability transition pore (MPTP), and this cardioprotective action of IPC is attenuated by hyperlipidaemia. The present study investigated the role of GSK-3beta in attenuation of cardioprotective effect of IPC, by hyperlipidaemia in the rat heart. Hyperlipidaemia was produced in rat by feeding high fat diet for six weeks. Isolated perfused rat heart was subjected to 30 min of ischemia followed by 120 min of reperfusion. Myocardial infarct size was estimated by triphenyltetrazolium chloride (TTC) staining and lactate dehydrogenase (LDH) and creatine kinase-MB (CK-MB) was analyzed from coronary effluent. IPC significantly decreased the myocardial infarct size and the release of LDH and CK-MB from normal rat heart. IPC induced myocardial protection was attenuated in hyperlipidaemic rat heart. However, cardioprotective effect of pharmacological preconditioning with GSK-3beta inhibitors i.e. Lithium Chloride (LiCl) (20mM), Indirubin - 3 Monooxime (1 microM) and 3-(2, 4-dichlorophenyl)-4-(1-methyl-1H-indol-3-yl)-1H-pyrrole-2, 5-dione (SB216763) (3 microM), was not attenuated. This differential attenuation by hyperlipidaemia, of IPC and pharmacological preconditioning induced cardioprotection is a new finding in our study. GSK-3beta inhibition is reported to increase the threshold of opening for MPTP during reperfusion. Administration of atractyloside (20 microM), an opener of MPTP, significantly attenuated the cardioprotective effect of IPC in normal heart, and pharmacological preconditioning in the hyperlipidaemic rat heart. Thus, the attenuation of cardioprotective effect of IPC in hyperlipidaemic heart may be due to inhibition of protective signaling pathways upstream of GSK-3beta and inhibition of opening of MPTP.