Ischaemic episodes of less than 5 minutes produce preconditioning but not stunning in the isolated rat heart

The aim of the present study was to examine whether ischaemic episodes of less than 5 min could induce preconditioning or stunning in the isolated rat heart. Hearts were subjected to total global ischaemia of 1, 2 and 4 min followed by 10 min of reperfusion before an 18-min main ischaemic period and 30 min of reperfusion. The effects on physiology, purine metabolism and anaerobic glycolysis were compared with a control group subjected to the main ischaemia only. The brief ischaemic episodes did not produce stunning based on the recovery of left ventricular developed pressure (LVDP) and heart rate (HR) product during the first reperfusion. Preconditioning of 11-14% increased recovery of LVDP x HR during the second reperfusion was observed in the 1- and 4-min group. In the 2-min group a low repayment of flow debt during the first reperfusion was associated with a slightly reduced recovery of LVDP x HR compared to the other preconditioned groups during the second reperfusion. Only in the 4-min group was preconditioning associated with fewer breakdown products of the purine nucleotide pool (adenosine) and anaerobic glycolysis (lactate) in both tissue and effluate after the main ischaemia. Preconditioning (reflected in recovery of function) could be produced with ischaemic episodes of less than 5 min that did not produce stunning. Thus, stunning is probably not the primary cause of preconditioning.