Cardioprotective-mimetics reduce myocardial infarct size in animals resistant to ischemic preconditioning.
BACKGROUND
Ischemic preconditioning (IPC) elicits two distinct windows of cardioprotection, an early phase that lasts for 1-2 h and a delayed phase that lasts for 24-72 h. However, there is conflicting data as to how long the heart is resistant to IPC-induced cardioprotection after the initial protection wanes, leading to the demonstration of IPC-resistance. This resistance to IPC appears to be dependent on the timing of the next IPC stimulus, the species of animals used and the model studied. Furthermore, the mechanisms responsible IPC-resistance are unknown. It is also important to demonstrate therapeutic interventions that will produce cardioprotection during this period of IPC-resistance.


RESULTS
To examine potential mechanisms responsible for acute IPC-induced resistance, the NHE-1 inhibitor EMD 85131 (2-methyl-5-methylsulfonyl-1-(1-pyrrollyl)-benzoylguanidine), which exerts its effects via mechanisms distinct from IPC, and the K(ATP) channel opener bimakalim, which bypasses the signaling mechanisms of IPC to directly open K(ATP) channels, were examined in a canine model of IPC-resistance. One 10 min. IPC stimulus followed by 10 min. of reperfusion produced a significant reduction in IS/AAR compared to Control (7.1 +/- 2.6% versus 26.0 +/- 6.2%; P < 0.05). However, IPC did not significantly protect the myocardium if a 2 h reperfusion period occurred between the initial IPC stimulus and the subsequent prolonged (60 min) ischemic challenge (IS/AAR: 22.5 +/- 4.8%: P > 0.05). Furthermore, hearts treated with IPC followed by 2 h of reperfusion were resistant to an additional IPC stimulus administered just prior to the subsequent 60 min. occlusion period (IS/AAR: 22.9 +/- 3.2%: P > 0.05). In contrast, administration of the NHE-1 inhibitor EMD 85131 (IS/AAR: 7.4 +/- 2.5%: P < 0.05) or the K(ATP) channel opener bimakalim (IS/AAR: 11.8 +/- 2.4%: P < 0.05) both afforded significant cardioprotection when administered at 2 h of reperfusion in previously preconditioned canine hearts resistant to IPC.


CONCLUSIONS
IPC resistance occurs in this canine model of ischemia-reperfusion injury. However, in spite of IPC resistance, hearts can still be pharmacologically protected by direct application of the K(ATP) channel opener bimakalim or the NHE inhibitor EMD 85131.
Gumina
Richard J
RJ
Interventional Cardiology Fellow, Division of Cardiovascular Medicine, Department of Internal Medicine, Mayo Clinic and Foundation, Rochester, MN, USA.
El Schultz
Jo
J
Moore
Jeanine
J
Beier
Norbert
N
Schelling
Pierre
P
Gross
Garrett J
GJ
D000818:Animals; D001549:Benzamides / Q000494:pharmacology / Q000627:therapeutic use; D001578:Benzopyrans / Q000494:pharmacology / Q000627:therapeutic use; D002316:Cardiotonic Agents / Q000494:pharmacology / Q000627:therapeutic use*; D004095:Dihydropyridines / Q000494:pharmacology / Q000627:therapeutic use; D004195:Disease Models, Animal; D004285:Dogs; D006321:Heart / Q000187:drug effects; D019157:Ischemic Preconditioning, Myocardial; D009203:Myocardial Infarction / Q000473:pathology / Q000517:prevention & control*; D015221:Potassium Channels / Q000819:agonists; D011758:Pyrroles / Q000494:pharmacology / Q000627:therapeutic use; D015427:Reperfusion Injury / Q000473:pathology / Q000517:prevention & control*; D017923:Sodium-Hydrogen Exchangers / Q000037:antagonists & inhibitors; D013997:Time Factors
D001549:Benzamides; D001578:Benzopyrans; D002316:Cardiotonic Agents; D004095:Dihydropyridines; C113375:N-diaminomethylene-2-methyl-5-methylsulfonyl-4-pyrrolobenzamide, hydrochloride; D015221:Potassium Channels; D011758:Pyrroles; D017923:Sodium-Hydrogen Exchangers; C069139:growth factor-activatable Na-H exchanger NHE-1; C061050:bimakalim