The effect of hypothermia during the period of calcium repletion on the calcium paradox.

Reperfusion of an isolated heart with a calcium-containing solution after a short calcium-free perfusion may result in irreversible cell damage: the calcium paradox. In this investigation the effect of hypothermia during reperfusion with calcium-containing solution on the calcium paradox damage in the isolated rat heart was studied. In addition, the effect of pre-cooling the heart during the calcium-free period was investigated. Creatine kinase release was used to define cell damage. Normothermic (37 degrees C) calcium-free perfusion followed by normothermic reperfusion with calcium-containing solution resulted in a massive release of CK. When the normothermic calcium-free perfusion was followed by hypothermic (10 degrees C) calcium-containing reperfusion, CK release was reduced by 20% (P less than 0.005). This CK release during reperfusion was further reduced by 55% and 80% when the normothermic calcium-free perfusion was followed by 5 or 10 min respectively of hypothermic calcium-free perfusion prior to the hypothermic calcium-containing reperfusion. The results show that hypothermia during the period of calcium repletion retards the sequence of events which ultimately results in release of large amounts of intracellular components.