Sex-specific responses to ischemic conditioning in myocardial infarction and stunning: Experimental insights

Abstract

This thesis investigates how ischemic conditioning strategies interact with biological sex and hormonal status to modulate myocardial responses to ischemia-reperfusion injury. It addresses both irreversible myocardial necrosis, defined as infarction, and reversible post-ischemic dysfunction, defined as myocardial stunning. Using well-established in vivo models in male and female Sprague-Dawley rats, the studies assessed the effects of ischemic preconditioning (IPC), remote perconditioning, postconditioning, and their combinations. Functional recovery was evaluated through serial echocardiography, infarct size was measured by TTC staining, and mechanistic insights were derived from phosphoproteomic and hormonal analyses. Study I: This study examined the dual effects of IPC in male rats, demonstrating that IPC not only limited infarct size but also increased the incidence of reversible contractile dysfunction. Phosphoproteomic profiling revealed early phosphorylation of sarcomeric and cytoskeletal proteins, suggesting that IPC may confer structural stabilization contributing to myocardial resilience. Study II: This study explored the role of sex and hormonal status in modulating the infarct-sparing effects of IPC. Infarct size varied across the estrous cycle, with proestrus-phase females, characterized by peak estradiol levels, exhibiting the smallest infarcts. Although IPC reduced infarct size across all groups, its v protective effect was attenuated under high-estrogen conditions, suggesting partial mechanistic overlap between IPC and endogenous hormonal signaling. Estradiol emerged as an independent predictor of reduced infarct size. Study III: This study compared the infarct-reducing efficacy of individual and combined conditioning strategies. While all interventions significantly reduced infarct size, combining them conferred no additional benefit. These findings support the existence of a protective ceiling effect, likely due to convergence on shared downstream signaling pathways. Study IV: This study established a female rat model of myocardial stunning and assessed whether estrous phase influenced the extent or resolution of dysfunction. IPC markedly increased the occurrence of stunning; however, no differences were observed between proestrus and estrus, suggesting that under mild ischemic conditions or following IPC, hormonal modulation of stunning may be limited or obscured. Conclusion: Collectively, these studies demonstrate that ischemic conditioning affects both the severity of irreversible injury and the course of functional recovery, with its efficacy influenced by biological sex and hormonal milieu. The findings underscore the importance of assessing functional outcomes alongside structural endpoints and support the systematic integration of sex-specific variables in experimental cardioprotection research.