Preconditioning preserves energy metabolism in prolonged low-flow ischemia

Background: A reduction in coronary flow leads to a parallel decrease in co ntractile function. Thus, a flow/function balance is established in the myo cardium under certain circumstances avoiding the development of impact of a preconditioning period on this critical balance was examined. Methods: In 116 isovolumetricalIy beating rat hearts, 3 h of hypoperfusion with 15 % of control coronary flow were performed followed by 1 h reperfusi on; 40 hearts served as controls. As a preconditioning period, in half of t he rat hearts a 5 min no-flow ischemia followed by 10 min reperfusion was p erformed, preceding the prolonged hypoperfusion. Results: Systolic function was identically reduced in both groups after 3 h hypoperfusion (LVP: 39 +/- 2 mmHg, 40 +/- 2 mmHg vs. controls 90 +/- 3 mmH g; p < 0.01). Without preconditioning hypoperfusion resulted in a marked in itial decrease in function. This period was followed by an adaptation to a higher steady state level of function compared with non-preconditioned hypo perfused hearts (p < 0.05). After preconditioning hypoperfusion directly re sulted in this level of contraction. Contractile reserve was reduced (p < 0 .01) identically in both hypoperfusion groups. Adenine nucleotides were dec reased (p < 0.01) after 3 h hypoperfusion to 2.1 +/- 0.2 mu mol/gww vs, con trols (4.7 +/- 0.2 mu mol/gww). After initial preconditioning adenine nucle otides were better preserved (3.2 +/- 0.2 mu mol/gww) going ahead with a cr eatine phosphate overshoot of 126 % (p < 0.01). After reperfusion, systolic function and contractile reserve were identical in both groups. Conclusion: A period of preceding no-flow ischemia followed by reperfusion modifies functional adaptation to hypoperfusion and preserves high energy p hosphates. Therefore, the metabolic balance during hypoperfusion is improve d by preconditioning, although no impact on contractile reserve or the func tional status of reperfused myocardium after low-flow ischemia can be seen.