Effects of Diazoxide post conditioning protection on myocardial ischemia-reperfusion injury in non-diabetic rats with stressed hyperglycemia / 中华危重病急救医学

ABSTRACT

Objective To observe the protective effects of Diazoxide (DZ) on myocardial ischemia and reperfusion (I/R) in non-diabetic rats with stressed hyperglycemia and to explore its possible mechanism. Methods The stressed hyperglycemia (SHG) myocardical I/R model was prepared by ligation of the left anterior descending branch of the coronary artery for 30 minutes and reperfusion for 120 minutes on the healthy adult Sprague-Dawley (SD) rats. Blood sugar was required up to 10 mmol/L in the qualified animal model after ischemia for 30 minutes. The 48 successful model rats were randomly divided into 4 groups (12 in each group) I/R group, low, medium and high dose DZ treated group (LIPO group, MIPO group, HIPO group). Sham-operated group (sham group) was only threaded without deligation. I/R group, LIPO group, MIPO group and HIPO group were challenged to 0.1% dimethyl sulfoxide (DMSO), DZ (0.1% DMSO dissolved) 4, 7, 10 mg/kg for 2 mL, respectively after ischemia for 25 minutes. Hemodynamics indicators were continuously monitored. After reperfusion for 120 minutes, blood glucose, serum creatine kinase (CK) concentration and lactate dehydrogenase (LDH) activity were detected, myocardial infarction area was analyzed by triphenyltetrazolium chloride (TTC) staining, myocardial ultrastructure was observed by electron microscope, expressions of phosphorylated protein kinase B (p-Akt) and phosphorylated glycogen synthase kinase-3β (p-GSK-3β) were detected by Western Blot. Results Compared with sham group, I/R group had an elevated blood glucose, decreased heart rate (HR), systolic diastolic dysfunction, increased myocardial enzymes. Obvious necrosis of myocardium, myocardial tissue edema, mitochondria swelling, cristae, disappearing glycogen granules were observed under electron microscope with TTC staining. After reperfusion for 120 minutes, comparing with I/R group, blood glucose of HIPO group was significantly increased (mmol/L 16.93±3.22 vs. 14.65±3.61, P < 0.05); the maximum rate of left ventricle internal pressure drop (-dp/dt max) of LIPO group was improved (mmHg/s -1 055±16 vs. -982±10, P < 0.05) and the infarct size was evidently shrunk [(32.45±3.54)% vs. (41.30±3.21)%, P < 0.05]; left ventricular systolic pressure (LVSP) of MIPO group and HIPO group [LVSP (mmHg, 1 mmHg = 0.133 kPa) 60±2, 74±4 vs. 54±4], left ventricular end-diastolic pressure [LVEDP (mmHg) 24.6±1.5, 18.9±1.3 vs. 27.9±1.6], the maximum rate of left ventricle internal pressure were increased [+dp/dt max (mmHg/s) 1 049±37, 1 262±75 vs. 975±17], and -dp/dt max (mmHg/s -1 068±21, -1 321±63 vs. -982±10) were improved in different degrees (all P < 0.05); CK (kU/L 10.7±0.5, 11.0±1.3 vs. 12.9±1.0), LDH (kU/L 6.8±0.2, 7.8±0.1 vs. 8.8±0.1) was evidently decreased (all P < 0.05), infarct size was smaller [(31.24±2.45)%, (30.81±2.68)% vs. (41.3±3.21)%, all P < 0.05], electron microscope showed that the myocardial injury was repaired. After reperfusion for 120 minutes, compared with sham group, expressions of p-Akt and p-GSK-3β in I/R group have obviously reduced (grey value 0 vs. 0.187±0.018, 0.110±0.045 vs. 0.200±0.081, both P < 0.05). Compared with I/R group, expressions of p-Akt in HIPO group and p-GSK-3β in LIPO group, MIPO group and HIPO group were obviously increased (grey value 0.101±0.009 vs. 0; 0.180±0.057, 0.270±0.062, 0.280±0.039 vs. 0.110±0.045, all P < 0.05). But there were significant increase in MIPO group and HIPO group. There was no significant difference in HR among different treatment groups. Conclusions I/R with SHG can significantly inhibit the activity of PI3K/Akt-GSK-3β signaling pathways, middle and high dose of DZ has a protective effect on I/R myocardium complicating with SHG, and middle dose will not lead to evident increase of blood glucose; DZ may act on GSK-3β through PI3K/Akt-GSK-3β signaling pathways, phosphorylate it and inhibit its activity, so as to develop the cardioprotective effect.