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Objective: The effects of transient low Ca<sup>2+</sup> reperfusion after ischaemia on metabolic and functional recovery were studied in isolated rat hearts. Methods: <sup>31</sup>P nuclear magnetic resonance (NMR) was used to monitor creatine phosphate, ATP, intracellular inorganic phosphate (Pi), and intracellular pH during control perfusion (15 min), total ischaemia (30 min), and reperfusion (30 min). During early reperfusion (0-10 min) perfusate [Ca<sup>2+</sup>] amounted to 1.3 (control group), 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, or 0.7 mmol·litre<sup>−1</sup>. During late reperfusion (10-30 min) perfusate [Ca<sup>2+</sup>] was 1.3 mmol·litre<sup>−1</sup>. Isolated rat hearts were used and perfused according to Langendorff. Results: Recovery of creatine phosphate during early reperfusion was partly abolished during late reperfusion in the 0.1-0.4 mmol·litre<sup>−1</sup> groups (p<0.01). In the 0.1 mmol·litre<sup>−1</sup> group creatine phosphate content after 30 min reperfusion was lower (p<0.05) than in the control group. Recovery of ATP during early reperfusion in the 0.3 mmol·litre<sup>−1</sup> group was better than in the control group (p<0.01). After 30 min reperfusion ATP recovery was better in the 0.3 mmol·litre<sup>−1</sup> group (p<0.01) and worse in the 0.1 mmol·litre<sup>−1</sup> group (p<0.05) than in the control group. Decline of Pi during early reperfusion was more pronounced in the 0.2 and 0.3 mmol·litre<sup>−1</sup> groups (p<0.01) and in the 0.5 and 0.6 mmol·litre<sup>−1</sup> groups (p<0.05) than in the control group. In the 0.3 and 0.4 mmol·litre<sup>−1</sup> groups, Pi after 30 min reperfusion was higher (p<0.05) than after 10 min reperfusion. After 30 min reperfusion left ventricular developed pressure, measured with an intraventricular balloon, was lower in the 0.1 mmol·litre<sup>−1</sup> group (p<0.01) than in the control group. Conclusions: The data show that under the experimental conditions used successive postischaemic reperfusion with 0.1 and 1.3 mmol·litre<sup>−1</sup> Ca<sup>2+</sup> resulted in poorer metabolic and functional recovery of the hearts than continuous reperfusion with 1.3 mmol·litre<sup>−1</sup> Ca<sup>2+</sup>. Postischaemic reperfusion with 0.1 mmol·litre<sup>−1</sup> Ca<sup>2+</sup> may predispose the heart to a mild calcium paradox. Successive reperfusion with 0.3 and 1.3 mmol·litre<sup>−1</sup> Ca<sup>2+</sup> was optimal in terms of ATP recovery but did not result in an increased recovery of left ventricular developed pressure. |
