An increase in the redox state during reperfusion contributes to the cardioprotective effect of GIK solution

Abstract

This study aimed at determining whether glucose-insulin-potassium (GIK) solutions modify the NADH/NAD(+) ratio during postischemic reperfusion and whether their cardioprotective effect can be attributed to this change in part through reduction of the mitochondrial reactive oxygen species (ROS) production. The hearts of 72 rats were perfused with a buffer containing glucose (5.5 mM) and hexanoate (0.5 mM). They were maintained in normoxia for 30 min and then subjected to low-flow ischemia (0.5% of the preischemic coronary flow for 20 min) followed by reperfusion (45 min). From the beginning of ischemia, the perfusate was subjected to various changes: enrichment with GIK solution, enrichment with lactate (2 mM), enrichment with pyruvate (2 mM), enrichment with pyruvate (2 mM) plus ethanol (2 mM), or no change for the control group. Left ventricular developed pressure, heart rate, coronary flow, and oxygen consumption were monitored throughout. The lactate/pyruvate ratio of the coronary effluent, known to reflect the cytosolic NADH/NAD(+) ratio and the fructose-6-phosphate/dihydroxyacetone-phosphate (F6P/DHAP) ratio of the reperfused myocardium, were evaluated. Mitochondrial ROS production was also estimated. The GIK solution improved the recovery of mechanical function during reperfusion. This was associated with an enhanced cytosolic NADH/NAD(+) ratio and reduced mitochondrial ROS production. The cardioprotection was also observed when the hearts were perfused with fluids known to increase the cytosolic NADH/NAD(+) ratio (lactate, pyruvate plus ethanol) compared with the other fluids (control and pyruvate groups). The hearts with a high mechanical recovery also displayed a low F6P/DHAP ratio, suggesting that an accelerated glycolysis rate may be responsible for increased cytosolic NADH production. In conclusion, the cardioprotection induced by GIK solutions could occur through an increase in the cytosolic NADH/NAD(+) ratio, leading to a decrease in mitochondrial ROS production.

Fig. 1.

Influence of glucose-insulin-potassium (GIK) solution on heart rate (A), diastolic pressure (B), left ventricular developed pressure (LVDP; C), and rate-pressure product (RPP; D) during perfusion with control medium (C) or medium enriched with GIK solution (G). The number of experiments was 10 per group. S ef., substrate effect; T ef., effect of reperfusion duration; CI, cross-interaction between those 2 factors; NS, not significant.

Fig. 2.

Influence of GIK solution on coronary flow (A) and myocardial oxygen consumption (B) during perfusion. The number of experiments was 10 per group. *P < 0.05 indicates a significant difference.

Fig. 3.

Influence of GIK solution on the lactate/pyruvate ratio of the coronary effluent. This parameter reflects the cytosolic NADH/NAD⁺ ratio. The number of experiments was 10 per group. *P < 0.05 indicates a significant difference.

Fig. 4.

Progression of the diastolic pressure during low-flow ischemia in the control, lactate, pyruvate, and pyruvate plus ethanol groups. The number of experiments was 10 per group. L, lactate-rich medium; P, pyruvate-rich medium; PE, medium enriched with pyruvate plus ethanol. ^a,b,c,d,eP < 0.05, different letters indicate significant differences as represented.

Fig. 5.

Progression of heart rate (A), diastolic pressure (B), LVDP (C), and RPP (D) during perfusion with control, lactate-rich, pyruvate-rich, and pyruvate plus ethanol-rich media. The number of experiments was 10 per group. ^{a,b,c,d,e,f,g}P < 0.05, different letters indicate significant differences as represented in each panel. Statistical analyses were performed only for the reperfusion period.

Fig. 6.

Progression of coronary flow (A) and myocardial oxygen consumption (B) during perfusion with control, lactate-rich, pyruvate-rich, and pyruvate plus ethanol-rich media. The number of experiments was 10 per group. ^{a,b,c,d,e,f,g}P < 0.05, different letters indicate significant differences as represented in each panel. Statistical analyses were performed only for the reperfusion period.

Fig. 7.

Influence of the different media on the contents of fructose-6-phosphate (fructose-6P; A) and dihydroxyacetone-phosphate (dihydroxyacetone-P; B) as well as the fructose-6P/dihydroxyacetone-P ratio (F6P/DHAP; C) in the myocardium at the end of the reperfusion period. The number of experiments was 10 per group. ^a,b,c,dP < 0.05, different letters indicate significant differences as represented in each panel.