NO trigger early preconditioning: relationship to mitochondrial K ATP channel. Am J Physiol Heart Circ Physiol 284: H299-H308, 2003. First published September 26, 2002 10.1152/ajpheart.00706.2002Reactive oxygen species (ROS) and nitric oxide (NO) are implicated in induction of ischemic preconditioning. However, the relationship between these oxidant signals and opening of the mitochondrial ATP-dependent potassium (K ATP) channel during early preconditioning is not fully understood. We observed preconditioning protection by hypoxia, exogenous H 2O2, or PKC activator PMA in cardiomyocytes subjected to 1-h ischemia and 3-h reperfusion. Protection was abolished by K ATP channel blocker 5-hydroxydecanoate (5-HD) in each case, indicating that these triggers must act upstream from the K ATP channel. Inhibitors of NO synthase abolished protection in preconditioned cells, suggesting that NO is also required for protection. DAF-2 fluorescence (NO sensitive) increased during hypoxic triggering. This was amplified by pinacidil and inhibited by 5-HD, indicating that NO is generated subsequent to K ATP channel activation. Exogenous NO during the triggering phase conferred protection blocked by 5-HD. Exogenous NO also restored protection abolished by 5-HD or N -nitro-L-arginine methyl ester in preconditioned cells. Antioxidants given during pinacidil or NO triggering abolished protection, confirming that ROS are generated by K ATP channel activation. Coadministration of H 2O2 and NO restored PMA-induced protection in 5-HD-treated cells, indicating that ROS and NO are required downstream from the K ATP channel. We conclude that ROS can trigger preconditioning by causing activation of the K ATP channel, which then induces generation of ROS and NO that are both required for preconditioning protection. hydrogen peroxide; nitric oxide; ischemia; cardiomyocytes PRECONDITIONING CONFERS PROTECTION against ischemiareperfusion injury in the heart. After a brief triggering stimulus is applied, the "early window" of protection begins within minutes and lasts for several hours. The persistence of protection after removal of the trigger indicates that a signal transduction pathway has been activated. Numerous triggers of preconditioning have been identified, including brief hypoxia/ischemia, opioids, ACh, bradykinin, activators of PKC, and pharmacological agents that activate the mitochondrial ATPdependent potassium (mitoK ATP ) channel (10,13,15,16,26,39,50). However, the signal transduction sequence activated by these triggers is not fully understood.Reactive oxygen species (ROS) have been implicated as participants in the signaling pathway involved in preconditioning triggering (1,2,4,23,41). We previously reported (42, 50) that exogenous H 2 O 2 induces preconditioning in cardiomyocytes and that mitochondrial ROS are involved in the triggering by hypoxia or by ACh administration. However, an interesting controversy has developed regarding the relationship between the mitoK ATP channel activation and the ROS signal during triggering. On...

Although ischemia-reperfusion (I/R) can initiate apoptosis, the timing and contribution of the mitochondrial/cytochrome c apoptosis death pathway to I/R injury is unclear. We studied the timing of cytochrome c release during I/R and whether subsequent caspase activation contributes to reperfusion injury in confluent chick cardiomyocytes. One-hour simulated ischemia followed by 3-h reperfusion resulted in significant cell death, with most cell death evident during the reperfusion phase and demonstrating mitochondrial cytochrome c release within 5 min after reperfusion. By contrast, cells exposed to prolonged ischemia for 4 h had only marginally increased cell death and no detectable cytochrome c release into the cytosol. Caspase activation could not be detected after ischemia only, but it significantly increased after reperfusion. Caspase inhibitors benzyloxycarbonyl-Val-Ala-Asp-fluoromethyl ketone, Ac-Asp-Gln-Thr-Asp-H, or benzyloxycarbonyl-Leu-Glu (Ome)-His-Asp-(Ome)-fluoromethyl ketone given only at reperfusion significantly attenuated cell death and resulted in return of contraction. Antixoxidants decreased cytochrome c release, nuclear condensation, and cell death. These results suggest that reperfusion oxidants initiate cytochrome c release within minutes, and apoptosis within hours, significant enough to increase cell death and contractile dysfunction.

timing of therapeutic hypothermia for cardiac ischemia is unknown. Our prior work suggests that ischemia with rapid reperfusion (I/R) in cardiomyocytes can be more damaging than prolonged ischemia alone. Also, these cardiomyocytes demonstrate protein kinase C (PKC) activation and nitric oxide (NO) signaling that confer protection against I/R injury. Thus we hypothesized that hypothermia will protect most using extended ischemia and early reperfusion cooling and is mediated via PKC and NO synthase (NOS). Chick cardiomyocytes were exposed to an established model of 1-h ischemia/3-h reperfusion, and the same field of initially contracting cells was monitored for viability and NO generation. Normothermic I/R resulted in 49.7 Ϯ 3.4% cell death. Hypothermia induction to 25°C was most protective (14.3 Ϯ 0.6% death, P Ͻ 0.001 vs. I/R control) when instituted during extended ischemia and early reperfusion, compared with induction after reperfusion (22.4 Ϯ 2.9% death). Protection was completely lost if onset of cooling was delayed by 15 min of reperfusion (45.0 Ϯ 8.2% death). Extended ischemia/early reperfusion cooling was associated with increased and sustained NO generation at reperfusion and decreased caspase-3 activation. The NOS inhibitor N -nitro-L-arginine methyl ester (200 M) reversed these changes and abrogated hypothermia protection. In addition, the PKC⑀ inhibitor myr-PKC⑀ v1-2 (5 M) also reversed NO production and hypothermia protection. In conclusion, therapeutic hypothermia initiated during extended ischemia/early reperfusion optimally protects cardiomyocytes from I/R injury. Such protection appears to be mediated by increased NO generation via activation of protein kinase C⑀; nitric oxide synthase.

EES recovery may require 48 h for C and 72 h for fT to return to baseline values. Furthermore, C and fT were only correlated immediately post-exercise. Future research should perform more frequent measurements throughout time course.

BackgroundThe cortisol awakening response (CAR) has been used as a biomarker of stress response in a multitude of psychological investigations. While a myriad of biochemical responses have been proposed to monitor responses to exercise training, the use of CAR within the exercise and sports sciences is currently limited and is a potentially underutilized variable. Therefore, the purpose of this review was to collate studies that incorporate both exercise and CAR, in an effort to better understand (a) whether CAR is a useful marker for monitoring exercise stress and (b) how CAR may be most appropriately used in future research.MethodsA systematic review of the literature was conducted, following PRISMA guidelines. Searches were conducted using PubMed, SportDISCUS, Scopus, and PsychInfo databases, using search terms related toCAR and exercise and physical activity.Results10,292 articles were identified in the initial search, with 32 studies included in the final analysis. No studies investigated the effects of laboratory-controlled exercise on CAR. Variable effects were observed, possibly due to inconsistencies in study design, methodology, population, and CAR analysis. The available literature suggests a threshold of exercise may be required to alter the HPA axis and affect CAR. Moreover, CAR may represent a combination of previous exercise load and upcoming stress, making current interpretation of field-based observational research challenging.ConclusionsMore research is needed to fully elucidate the influence of exercise on CAR and address a number of gaps in the literature, including controlling exercise load, consistent sample collection, and CAR calculation and analysis.