Acute hyperglycemia exacerbates myocardial ischemia/reperfusion injury and blunts cardioprotective effect of GIK

Abstract

. Acute hyperglycemia exacerbates myocardial ischemia/reperfusion injury and blunts cardioprotective effect of GIK. Am J Physiol Endocrinol Metab 293: E629-E635, 2007. First published May 22, 2007; doi:10.1152/ajpendo.00221.2007.-There is a close association between hyperglycemia and increased risk of mortality after acute myocardial infarction (AMI). However, whether acute hyperglycemia exacerbates myocardial ischemia/reperfusion (MI/R) injury remains unclear. We observed the effects of acute hyperglycemia on MI/R injury and on the cardioprotective effect of glucose-insulin-potassium (GIK). Male rats were subjected to 30 min of myocardial ischemia and 6 h of reperfusion. Rats were randomly received one of the following treatments (at 4 ml ⅐ kg Ϫ1 ⅐ h Ϫ1 iv): Vehicle, GIK (GIK during reperfusion; glucose: 200g/l, insulin: 60 U/l, KCL: 60 mmol/l), HG (high glucose during ischemia; glucose:500 g/l), GIK ϩ HG (HG during I and GIK during R) or GIK ϩ wortmannin (GIK during R and wortmannin 15 min before R). Blood glucose, plasma insulin concentration and left ventricular pressure (LVP) were monitored throughout the experiments. Hyperglycemia during ischemia not only significantly increased myocardial apoptosis (23.6 Ϯ 1.7% vs. 18.8 Ϯ 1.4%, P Ͻ 0.05 vs. vehicle), increased infarct size (IS) (45.6 Ϯ 3.0% vs. 37.6 Ϯ 2.0%, P Ͻ 0.05 vs. vehicle), decreased Akt and GSK-3␤ phosphorylations (0.5 Ϯ 0.2 and 0.6 Ϯ 0.1% fold of vehicle, respectively, P Ͻ 0.05 vs. vehicle) following MI/R, but almost completely blocked the cardioprotective effect afforded by GIK, as evidenced by significantly increased apoptotic index (19.1 Ϯ 2.0 vs. 10.3 Ϯ 1.2%, P Ͻ 0.01 vs. GIK), increased myocardial IS (39.2 Ϯ 2.8 vs. 27.2 Ϯ 2.1%, P Ͻ 0.01 vs. GIK), decreased Akt phosphorylation (1.1 Ϯ 0.1 vs. 1.7 Ϯ 0.2%, P Ͻ 0.01 vs. GIK) and GSK-3␤ phosphorylation (1.4 Ϯ 0.2 vs. 2.3 Ϯ 0.2%, P Ͻ 0.05 vs. GIK). Hyperglycemia significantly exacerbates MI/R injury and blocks the cardioprotective effect afforded by GIK, which is, at least in part, due to hyperglycemia-induced decrease of myocardial Akt activation.Akt; glucose-insulin-potassium IN PATIENTS WITH ACUTE MYOCARDIAL INFARCTION (AMI), stress hyperglycemia can commonly be observed. An association between hyperglycemia and an increased risk of mortality and poor prognosis after AMI was well noted in patients with or without diabetes (1, 21). Mechanisms for the association between stress hyperglycemia and adverse outcomes after AMI in nondiabetic patients are not well understood. Additional studies showed that acute hyperglycemia in AMI patients without diabetes was independently associated with larger enzymatic infarct size and higher long-term mortality rates after AMI (22). These results suggest that poor outcomes of patients with AMI may be related to hyperglycemia. However, direct evidence to support a causative role of acute hyperglycemia in exacerbating myocardial ischemia/reperfusion (MI/R) injury is not currently available, and the underlying mechanisms remain unidentified.Glucose-insulin-potassiu...

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