Endogenous myocardial norepinephrine is not essential for ischemic preconditioning in rabbit heart

Assessment of oxidative stress and antioxidant property using electron spin resonance (ESR) spectroscopy

The pathophysiology of hypertension or stroke is associated with an excess of ROS generation in the vascular system, and results in induction of various pathological cascades of cerebrovascular damage. We have demonstrated that electron spin resonance methods using a spin trap or spin probe will be useful for understanding redox status under conditions of oxidative stress in the spontaneously hypertensive rat or stroke-prone spontaneously hypertensive rat brain. We have used electron spin resonance imaging and noninvasive L-band electron spin resonance to characterize the higher degree of brain oxidative stress in the stroke-prone spontaneously hypertensive rat and spontaneously hypertensive rat than in the Wistar-Kyoto rat brain, and the lower extent of oxidative stress in the spontaneously hypertensive rat than in the stroke-prone spontaneously hypertensive rat brain. Indeed, we may be able to confirm propofol medium-chain triglyceride/long-chain triglyceride (MCT/LCT) as neuroprotective anesthesia and crocetin as antioxidant food factor against human stroke after screening for antioxidant properties in stroke models such as stroke-prone spontaneously hypertensive rat. Thus, our electron spin resonance biomedical application suggests that it could be used to assess antioxidant effects on oxidative stress in the brain using spontaneously hypertensive rat and stroke-prone spontaneously hypertensive rat. We hope that further advances in the instrumentation used for electron spin resonance imaging and the development of optimized nontoxic spin probes will make this technology even more promising for novel clinical prediction or noninvasive diagnosis of human stroke. After screening drugs or foods for antioxidant property using in vitro or in vivo electron spin resonance assessment, it will be possible to find and develop novel drugs or food factors with such properties for the prevention of stroke in the near future.

Pathophysiology of myocardial reperfusion injury: preconditioning, postconditioning, and translational aspects of protective measures

Heart diseases due to myocardial ischemia, such as myocardial infarction or ischemic heart failure, are major causes of death in developed countries, and their number is unfortunately still growing. Preliminary exploration into the pathophysiology of ischemia-reperfusion injury, together with the accumulation of clinical evidence, led to the discovery of ischemic preconditioning, which has been the main hypothesis for over three decades for how ischemia-reperfusion injury can be attenuated. The subcellular pathophysiological mechanism of ischemia-reperfusion injury and preconditioning-induced cardioprotection is not well understood, but extensive research into components, including autacoids, ion channels, receptors, subcellular signaling cascades, and mitochondrial modulators, as well as strategies for modulating these components, has made evolutional progress. Owing to the accumulation of both basic and clinical evidence, the idea of ischemic postconditioning with a cardioprotective potential has been discovered and established, making it possible to apply this knowledge in the clinical setting after ischemia-reperfusion insult. Another a great outcome has been the launch of translational studies that apply basic findings for manipulating ischemia-reperfusion injury into practical clinical treatments against ischemic heart diseases. In this review, we discuss the current findings regarding the fundamental pathophysiological mechanisms of ischemia-reperfusion injury, the associated protective mechanisms of ischemic pre- and postconditioning, and the potential seeds for molecular, pharmacological, or mechanical treatments against ischemia-reperfusion injury, as well as subsequent adverse outcomes by modulation of subcellular signaling mechanisms (especially mitochondrial function). We also review emerging translational clinical trials and the subsistent clinical comorbidities that need to be overcome to make these trials applicable in clinical medicine.

Role of the autonomic nervous system in cardioprotection by remote preconditioning in isoflurane-anaesthetized dogs

AIMS

Remote ischaemic preconditioning (rIPC) protects cardiac and non-cardiac tissues against ischaemic injury. Although there is increased demand to investigate its potential clinical applicability, fundamental mechanisms responsible for rIPC-mediated protection remain unresolved. We examined in isoflurane-anaesthetized dogs whether an intact cardiac nervous system was necessary to mediate rIPC protection against ischaemic injury.

METHODS AND RESULTS

Dogs were randomly allocated to six groups: 1, control (CON, no-rIPC); 2, rIPC (4 × 5 min renal artery occlusion/reperfusion); 3, autonomic ganglionic blockade with hexamethonium (HEX, no-rIPC; 20 mg/kg iv); 4, HEX + rIPC; 5, cardiac decentralization by surgical ablation of extracardiac nerves (DCN, no-rIPC); and 6, DCN + rIPC. All dogs underwent 60 min coronary occlusion and 180 min reperfusion; cardiac haemodynamic parameters were monitored. Regional blood flow (microspheres) in the heart and kidneys was assessed. Necrotic tissue was visualized using triphenyltetrazolium staining and related to anatomic risk zone size (area at risk; P = NS between groups) and coronary collateral blood flow. Infarct size (% AAR) was 29 ± 5 (mean ± 1 SD) in CON and 15 ± 4 in rIPC dogs (P = 0.001 vs. CON); 24 ± 3 in HEX vs. 12 ± 2 in HEX + rIPC (P = 0.001 vs. HEX); and 20 ± 2 in DCN vs. 12 ± 4 in DCN + rIPC (P = 0.001 vs. DCN). In CON dogs, infarct size was inversely related to coronary collateral flow; this relation was shifted downwards in all groups pre-treated with rIPC.

CONCLUSION

We report robust myocardial protection by rIPC against ischaemic injury in canines that was not abrogated by either pharmacological or surgical decentralization of cardiac nerves.

Preemptive, but not reactive, spinal cord stimulation mitigates transient ischemia-induced myocardial infarction via cardiac adrenergic neurons

Our objective was to determine whether electrical neuromodulation using spinal cord stimulation (SCS) mitigates transient ischemia-induced ventricular infarction and, if so, whether adrenergic neurons are involved in such cardioprotection. The hearts of anesthetized rabbits, subjected to 30 min of left anterior descending coronary arterial occlusion (CAO) followed by 3 h of reperfusion (control), were compared with those with preemptive SCS (starting 15 min before and continuing throughout the 30-min CAO) or reactive SCS (started at 1 or 28 min of CAO). For SCS, the dorsal C8-T2 segments of the spinal cord were stimulated electrically (50 Hz, 0.2 ms, 90% of motor threshold). For preemptive SCS, separate groups of animals were pretreated 15 min before SCS onset with 1) vehicle, 2) prazosin (alpha(1)-adrenoceptor blockade), or 3) timolol (beta-adrenoceptor blockade). Infarct size (IS), measured with tetrazolium, was expressed as a percentage of risk zone. In controls exposed to 30 min of CAO, IS was 36.4 +/- 9.5% (SD). Preemptive SCS reduced IS to 21.8 +/- 6.8% (P < 0.001). Preemptive SCS-mediated infarct reduction was eliminated by prazosin (36.6 +/- 8.8%) and blunted by timolol (29.4 +/- 7.5%). Reactive SCS did not reduce IS. SCS increased phosphorylation of cardiac PKC. SCS did not alter blood pressure or heart rate. We conclude that preemptive SCS reduces the size of infarcts induced by transient CAO; such cardioprotection involves cardiac adrenergic neurons.

Preservation of ischemia and isoflurane-induced preconditioning after brain death in rabbit hearts

We sought to determine whether brain death-induced catecholamine release preconditions the heart, and if not, whether it precludes further protection by repetitive ischemia or isoflurane. Anesthetized rabbits underwent 30 min of coronary occlusion and 4 h of reperfusion. The effect on infarct size of either no intervention (controls), ischemic preconditioning (IPC), or isoflurane inhalation (Iso) was evaluated with or without previous brain death (BD) induced by subdural balloon inflation. Plasma catecholamine levels were measured at several time points. Although it dramatically increase plasma catecholamine levels, BD failed to reduce infarct size that averaged 0.49 +/- 0.34 without BD versus 0.45 +/- 0.27 g with BD. IPC and Iso, alone as well as after BD, significantly reduced infarct size that averaged 0.11 +/- 0.04, 0.21 +/- 0.15, 0.10 +/- 0.09, and 0.22 +/- 0.10 g in IPC, Iso, BD + IPC, and BD + Iso groups, respectively (means +/- SD, P < 0.05 vs. controls). BD-induced catecholamines "storm" does not precondition the rabbit heart that however retains the ability to be protected by repetition of brief ischemia or isoflurane inhalation.