title: Postconditioning's protection is not dependent on circulating blood factors or cells but involves adenosine receptors and requires PI3-kinase and guanylyl cyclase activation.
abstract: Protection from postconditioning has been documented in in situ animal models and it has been proposed that it is targeting circulating leukocytes. We therefore tested whether postconditioning can protect leukocyte-free, buffer-perfused rabbit hearts. Infarct size was measured with triphenyltetrazolium staining. In control hearts undergoing 30 min of regional ischemia and 2 h of reperfusion, 33.3 +/- 2.2% of the risk zone infarcted. The protocol previously used in open-chest animals of four postconditioning cycles of 30 s reperfusion/30 s ischemia starting at the beginning of reperfusion decreased infarction to only 24.8 +/- 2.5% of the risk zone in these isolated hearts. Because of the meager protection induced by four 30 s postconditioning cycles, we evaluated the effect of postconditioning with 6 cycles of 10 s reperfusion/10 s ischemia starting at the beginning of reperfusion. Robust salvage was seen with only 10.4 +/- 3.4% of the risk zone infarcting (p < 0.001 vs control and p < 0.003 vs 4 cycles of 30 s ischemia). The 10s protocol was used in all studies of signal transduction. Wortmannin (100 nM), a phosphatidylinositol 3- (PI3-) kinase antagonist, infused for 20 min starting 5 min before reperfusion, blocked postconditioning's, protection (31.2 +/- 4.2% infarction) as did 1H-[1,2,4]oxadiazole[4,3-a]quinoxalin-1-one (ODQ) (2 microM) a guanylyl cyclase inhibitor (36.9 +/- 5.3%) and 8-p-(sulfophenyl) theophylline (SPT) (100 microM), a non-specific adenosine receptor blocker (34.2 +/- 2.8%). Thus, postconditioning's protection is not dependent on circulating blood factors or cells, and its anti-infarct effect appears to require PI3-kinase activation, stimulation of guanylyl cyclase and occupancy of adenosine receptors. These signaling steps have also been identified in preconditioning and during pharmacologic cardioprotection and suggest commonality of a protective mechanism.
authors.affiliation: Dept. of Physiology, MSB 3050 University of South Alabama, College of Medicine, Mobile (AL) 36688, USA.
authors.forename: Xi-Ming
authors.initials: XM
authors.lastname: Yang
authors.forename: Sebastian
authors.initials: S
authors.lastname: Philipp
authors.forename: James M
authors.initials: JM
authors.lastname: Downey
authors.forename: Michael V
authors.initials: MV
authors.lastname: Cohen
mesh_terms: D000818:Animals; D005260:Female; D006162:Guanylate Cyclase / Q000502:physiology*; D019157:Ischemic Preconditioning, Myocardial; D008297:Male; D009203:Myocardial Infarction / Q000097:blood / Q000201:enzymology / Q000473:pathology / Q000517:prevention & control*; D019869:Phosphatidylinositol 3-Kinases / Q000502:physiology*; D011817:Rabbits; D018047:Receptors, Purinergic P1 / Q000502:physiology*
chemical_list: D018047:Receptors, Purinergic P1; D019869:Phosphatidylinositol 3-Kinases; D006162:Guanylate Cyclase