title: Second window of protection following myocardial preconditioning: an essential role for PI3 kinase and p70S6 kinase.
abstract: Ischaemic preconditioning (IPC) protects the heart against myocardial infarction acutely as well as several hours later (e.g. 24-48 h). The mechanism of the profound cardioprotection is not completely explored. We hypothesized that PI3K/PDK1/Akt/mTOR/p70S6K-mediated pro-survival pathway is involved in delayed cardioprotection induced by IPC. Under Hypnorm-Diazepam anaesthesia, male New Zealand White rabbits were either sham-operated (SC) or preconditioned by four cycles of 5-min ischaemia and 10-min reperfusion on day 1. Twenty-four hours after recovery, the animals were anaesthetized with sodium pentobarbitone and subjected to 30-min ischaemia followed by 180-min reperfusion. Wortmannin (0.6 mg/kg, i.v.), an irreversible PI3 kinase (PI3K) inhibitor, rapamycin (0.25 mg/kg, i.v.), which prevents the phosphorylation of p70S6 kinase (p70S6K), or DMSO (control vehicle) was given 15 min prior to IPC. IPC significantly reduced infarct size compared to the control group (SC) (31.9 +/- 5.8% (n = 7) vs. 54.9 +/- 2.9% (n = 6), P < 0.05). Wortmannin and rapamycin alone had no effect on infarct size (56.3 +/- 1.6% (n = 6) and 54.7 +/- 3.8% (n = 6), respectively). However, when wortmannin or rapamycin were given prior to IPC the protection was completely abolished (49.9 +/- 2.8% (n = 6), 45.1 +/- 4.6% (n = 7), P < 0.05 vs. IPC). Western blot analysis showed that wortmannin, at a dose of 0.6 mg/kg, and rapamycin, at a dose of 0.25 mg/kg, were sufficient to prevent phosphorylation of Akt and p70S6K, respectively, when the inhibitors were given prior to IPC. We conclude that PI3K/PDK1/Akt/mTOR/p70S6K-signalling pathway plays an essential role in the development of the cardioprotection against infarction in rabbits.
authors.affiliation: The Hatter Institute, University College London Hospital and Medical School, Grafton Way, London WC1E 6DB, UK.
authors.forename: Adrienn
authors.initials: A
authors.lastname: Kis
authors.forename: Derek M
authors.initials: DM
authors.lastname: Yellon
authors.forename: Gary F
authors.initials: GF
authors.lastname: Baxter
mesh_terms: D000730:Androstadienes / Q000494:pharmacology; D000818:Animals; D004347:Drug Interactions; D004791:Enzyme Inhibitors / Q000494:pharmacology; D019157:Ischemic Preconditioning, Myocardial; D008297:Male; D008954:Models, Biological; D009203:Myocardial Infarction / Q000473:pathology / Q000517:prevention & control; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D000081082:Phosphoinositide-3 Kinase Inhibitors; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000187:drug effects / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt; D011817:Rabbits; D038762:Ribosomal Protein S6 Kinases, 70-kDa / Q000037:antagonists & inhibitors / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects; D020123:Sirolimus / Q000494:pharmacology; D013997:Time Factors; D000077191:Wortmannin
chemical_list: D000730:Androstadienes; D004791:Enzyme Inhibitors; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D038762:Ribosomal Protein S6 Kinases, 70-kDa; D020123:Sirolimus; D000077191:Wortmannin