Mechanism of the hypoxia inducible factor 1/hypoxic response element pathway in rat myocardial ischemia/diazoxide post‑conditioning.

Ischemic post‑conditioning (IPO) and diazoxide post‑conditioning (DPO) has been proven to reduce myocardial ischemia reperfusion injury (MIRI); however, the mechanisms of IPO/DPO are still not clear. The present study aimed to investigate whether mitochondrial ATP‑sensitive potassium channels (mitoKATP) channels are activated by IPO/DPO, which may further activate the hypoxia inducible factor 1/hypoxic response element (HIF‑1/HRE) pathway to mitigate MIRI. Using a Langendorff perfusion device, healthy male (250‑300 g) Sprague Dawley rat hearts were randomly divided into the following groups. Group N was aerobically perfused with K‑H solution for 120 min. Group ischaemia/reperfusion (I/R) was aerobically perfused for 20 min, then subjected to 40 min hypoxia plus 60 min reperfusion. Group IPO was treated like the I/R group, but with 10 sec of hypoxia plus 10 sec of reperfusion for six rounds before reperfusion. Group DPO was exposed to 50 µM diazoxide for 5 min before reperfusion and otherwise treated the same as group I/R. In groups IPO+5‑hydroxydecanoic acid (5HD), DPO+5HD and I/R+5HD, exposure to 100 µM 5HD (a mitoKATP channel specific blocker) for 5 min before reperfusion as described for groups IPO, DPO and I/R, respectively. In groups IPO+2‑methoxyestradiol (2ME2), DPO+2ME2 and I/R+2ME2, exposure to 2 µM 2ME2 (a HIF‑1α specific blocker) for 10 min before reperfusion as described for groups IPO, DPO and I/R respectively. Cardiac hemodynamics, myocardial injury and the expression of HIF‑1/HRE pathway [HIF‑1α, heme oxygenase (HO‑1), inducible nitric oxide synthase (iNOS) and vascular endothelial growth factor (VEGF)] were detected in each group. The infarct size and mitochondrial Flameng scores of groups IPO/DPO were significantly decreased compared with the I/R group (P<0.05), but the myocardial protective effects of IPO/DPO could be eliminated by 5HD or 2ME2 (P<0.05). In addition, IPO/DPO could increase the mRNA expression of HIF‑1α and the downstream factors of the HIF‑1/HRE pathway (the mRNA and protein expression of HO‑1, iNOS and VEGF; P<0.05). However, the myocardial protective effects and the activation the HIF‑1/HRE pathway mediated by IPO/DPO could be eliminated by 5HD or 2ME2 (P<0.05). Therefore, the activation of the HIF‑1/HRE pathway by opening mitoKATP channels may work with the mechanism of IPO/DPO in reducing MIRI.