Transient hypocalcemic reperfusion does not improve postischemic recovery in the rat heart after preservation with St. Thomas’ Hospital cardioplegic solution

Abstract

We used the isolated perfused working rat heart to investigate the effects of transient hypocalcemic reperfusion after cardioplegic arrest with the St. Thomas' Hospital cardioplegic solution and 25 minutes of global normothermic (37 degrees C) ischemia. Hearts were reperfused (Langendorff mode) transiently (20 minutes) with solutions containing various concentrations of calcium; this was followed by 30 minutes of reperfusion with standard (1.4 mmol/L, the physiologic concentration) calcium buffer (10 minutes in the Langendorff mode and 20 minutes in the working mode). Recovery of cardiac output in control hearts (calcium concentration 1.4 mmol/L throughout) was 51.7% +/- 4.6%; in hearts transiently reperfused with hypocalcemic buffer (0.25, 0.5, 0.75, or 1.0 mmol/L) the recoveries of cardiac output were 49.3% +/- 6.4%, 52.2% +/- 7.2%, 58.7% +/- 3.2%, and 47.2 +/- 4.7%, respectively (all not significant), whereas recovery was only 14.7% +/- 2.8% (p less than 0.05) in hearts transiently reperfused with calcium 0.1 mmol/L. Creatine kinase leakage was significantly (p less than 0.05) greater in the group reperfused with calcium 0.1 mmol/L, but it did not vary significantly between the other groups. Tissue high-energy phosphate content was similar and in the normal range in all groups except for the group reperfused with calcium 0.1 mmol/L. In further experiments, the duration of hypocalcemic (0.5 mmol/L) reperfusion was varied (0, 5, 10, 15, 20, or 30 minutes). No significant differences in recovery of cardiac output were observed (58.2% +/- 5.0%, 52.3% +/- 5.7%, 52.0% +/- 8.2%, 61.2% +/- 5.0%, 62.2% +/- 4.3%, and 66.2% +/- 3.2%, respectively). In additional studies, the standard calcium concentration (1.4 mmol/L) used before and after ischemia was replaced by hypercalcemic solution (2.5 mmol/L). Despite this, transient (10 minutes) hypocalcemic (0.5 mmol/L) reperfusion did not improve recovery. Finally, studies were undertaken with a longer duration of ischemia (40 minutes), and although recovery of cardiac output in the hypocalcemic group (0.5 mmol/L for 10 minutes) tended to be higher than in the control group (29.7% +/- 4.8% versus 18.5% +/- 4.9%, respectively), statistical significance was not achieved. We conclude that in these studies transient hypocalcemic reperfusion did not afford any additional protection over and above that afforded by cardioplegia alone.