Beneficial effect of glucose on short-term, perfusion-pressure induced changes of contractile efficiency in isolated rabbit hearts

Journal of Clinical and Basic Cardiology 2000; 3 (2): 135-139

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Keywords: Effizienz,  hibernation,  isoliertes Herz,  Kaninchen,  Substrat,  efficiency,  isolated heart,  myocardial hibernation,  rabbit,  substrate

Objective: As adaptation to decreased coronary perfusion, both mechanical function and oxygen consumption are reduced in short-term hibernating myocardium. Changes in the energy supply-demand balance are reflected by changes in contractile efficiency (Econ; = relation between oxygen consumption and the pressure volume area; PVA). We investigated the influence of supplementation with free fatty acids (FFA) alone versus a combination of FFA with glucose on Econ in moderately or severely hypoperfused myocardium. Methods: 30 isolated rabbit hearts were perfused with buffer containing either 1.4 mM FFA (group FA) or 1.4 mM FFA plus 11 mM glucose (group FAG). During control, the coronary arterial pressure (CAP) was 90 mmHg. CAP was reduced either to 60 mmHg (n = 19, HYP60) or to 30 mmHg (n = 11, HYP30). Results: Myocardial systolic function (aortic flow, peak left ventricular pressure, slope of the end-systolic pressure volume relation, and PVA) did not show any dependency on the substrate composition during control, HYP60, HYP30, and reperfusion. In group FA, hypoperfusion did not significantly affect the slope of the MVO2-PVA relation compared with control: 40.1 ± 15.2 vs. 37.6 ± 12.3 (HYP60) and 29.8 ± 9.2 vs. 30.3 ± 10.4 µl/beat/(mmHg x ml)10-4 (HYP30). In group FAG, the slope decreased during HYP60 (26.3 ± 3.0 vs. 16.5 ± 1.9, *p < 0.05) and during HYP30 (21.8 ± 8.5 vs. 20.5 ± 4.5 µl/beat/(mmHg x ml)x 10-4; n.s.). Conclusion: Additional supply with glucose in comparison to FFA alone increases Econ during moderate hypoperfusion. Since Econ was not significantly changed during severe hypoperfusion, when no autoprotection is possible, this might reflect autoprotective changes in metabolic pathways facilitated by glucose. The change in Econ might be explained by a beneficial effect of glucose on supply-demand balance, e.g. lower energy cost of carbohydrate oxidation in comparison to FFA oxidation and diminished deleterious effects of FFA oxidation on the myocardium. J Clin Basic Cardiol 2000; 3: 135-9.