Postconditioning the isolated working rat heart.

Purpose: Despite the attention focussed on postconditioning (postC; brief cycles of reperfusion/ischaemia at the onset of reperfusion, conferring cardioprotection against reperfusion injury), an infarct sparing effect for postC in the isolated working heart model has not been reported. The purpose of this study was to develop a cardioprotective postC protocol in this model.

Methods: Hearts from male Wistar rats (210-350 g) were perfused either retrogradely (Langendorff) or in the working mode. For functional studies 30 or 35 min global ischaemia (GI) and 20 or 25 min GI were applied in the Langendorff and working heart models respectively. Infarct size was measured after 35 min regional ischaemia (RI) in both models. In the latter studies hearts were subdivided into low (36.5 degrees C) and high (37 degrees C) temperature groups (during both ischaemia and initial reperfusion). In all groups hearts were either freely reperfused (nonPostC) or postconditioned (postC) by 6x10 s ischaemia/reperfusion cycles.

Results: In both perfusion modes postC only elicited an infarct sparing effect after a slight elevation in temperature to 37 degrees C (Langendorff: L-nonPostC=47.99+/-3.31% vs. L-postC=27.81+/-2.49%, p<0.0001; and work=W-nonPostC: 35.81+/-3.67% vs. W-postC=17.74+/-2.72%, p<0.001). However, only in the Langendorff group could postC conserve post-ischaemic function, while no significant recoveries were seen in the working hearts.

Conclusion: We demonstrated an infarct sparing effect for postC in the working heart model, which unlike the Langendorff model, was not associated with functional preservation. The infarct sparing effect of postC in both models was however extremely sensitive to even slight fluctuations in temperature.