Ischemic postconditioning does not provide cardioprotection from long-term ischemic injury in isolated male or female rat hearts¹

Background: Ischemic postconditioning (PoC) is a cardio-protective strategy in which initial reperfusion is interrupted by episodes of ischemia. It is unclear whether PoC can be achieved in the Langendorff perfused rat heart model. We investigated (1) whether postconditioning occurs in Langendorff perfused rat heart and (2) whether there is a gender-specific response to PoC. Materials and Methods: Male/female rat hearts (n = 8/group) were subjected to 30 min of equilibration, 30 min of ischemia, and 120 min of reperfusion (Control). PoC was induced by 6 cycles (PoC 6c10s), 3 cycles (PoC 3c10s), or 2 cycles (PoC 2c10s) of 10 s reperfusion/10 s ischemia. Rate pressure product (RPP) and infarct size were measured. Male rats (n = 7/group) were subjected in vivo to 30 min left coronary ligation followed by 24 h of reperfusion (Control) or PoC 6c10s and 24 h of reperfusion. Results: Recovery of RPP was 18% ± 4% in male Control versus 17% ± 2% for 6c10s, 16% ± 1% for 3c10s, and 15% ± 3% for 2c10s. Female Control hearts recovered 25% ± 3% of their RPP versus 21% ± 2% for 6c10s. Infarct size was 25% ± 3% for male Control versus 26% ± 3% for 6c10s, 30% ± 2% for 3c10s, 28% ± 1% for 2c10s, and 30% ± 2% for female Control versus 29% ± 2% in 6c10s. In vivo infarct size for Control and PoC 6c10s was 44% ± 3% and 28% ± 5%, respectively (P < 0.05). Conclusions: In the Langendorff perfused rat hearts, none of the PoC protocols improved myocardial tolerance to ischemia reperfusion injury nor decreased infarct size; however, in vivo postconditioning did confer protection. The lack of protection in the isolated hearts was not gender specific.