Nitroglycerin induces late preconditioning against arrhythmias but not stunning in conscious sheep

Protective or Inhibitory Effect of Pharmacological Therapy on Cardiac Ischemic Preconditioning: A Literature Review

Ischemic preconditioning (IP) is an innate phenomenon, triggered by brief, non-lethal cycles of ischemia/reperfusion applied to a tissue or organ that confers tolerance to a subsequent more prolonged ischemic event. Once started, it can reduce the severity of myocardial ischemia associated with some clinical situations, such as percutaneous coronary intervention (PCI) and intermittent aortic clamping during coronary artery bypass graft surgery (CABG). Although the mechanisms underlying IP have not been completely elucidated, several studies have shown that this phenomenon involves the participation of cell triggers, intracellular signaling pathways, and end-effectors. Understanding this mechanism enables the development of preconditioning mimetic agents. It is known that a range of medications that activate the signaling cascades at different cellular levels can interfere with both the stimulation and the blockade of IP. Investigations of signaling pathways underlying ischemic conditioning have identified a number of therapeutic targets for pharmacological manipulation. This review aims to present and discuss the effects of several medications on myocardial IP.

Comparative effects of verapamil, nicardipine, and nitroglycerin on myocardial ischemia/reperfusion injury

The aim of this experiment was to establish whether verapamil, nicardipine, and nitroglycerin have (1) infarct size-limiting effects and (2) antiarrhythmic effects in in vivo rabbit hearts during ischemia/reperfusion. Rabbits received regional ischemia by 30 min of left anterior descending coronary artery occlusion followed by 3 hours of reperfusion under ketamine and xylazine anesthesia. The animals were randomly assigned to the following 4 treatment groups: a control group, a verapamil group, a nicardipine group, and a nitroglycerin group. A continuous infusion of verapamil, nicardipine, or nitroglycerin was initiated 5 min prior to ischemia. Infarct size/area at risk decreased in verapamil, and nitroglycerin. The incidence of ischemia-induced arrhythmia decreased in nicardipine, verapamil and nitroglycerin. The incidence of reperfusion-induced arrhythmias decreased in verapamil and nitroglycerin. From the present experimental results, verapamil and nitroglycerin rather than nicardipine did afford significant protection to the heart subjected to ischemia and reperfusion in a rabbit model.

Periodic acceleration (pGz) prior to whole body ischemia reperfusion injury provides early cardioprotective preconditioning

AIMS

Periodic acceleration (pGz) is a method that applies repetitive sinusoidal head-to-foot motion to the horizontally positioned body. pGz adds pulses to the circulation as a function of frequency, thereby increasing shear stress to the endothelium. Pulsatile shear stress increases release of cardioprotective endothelial-derived nitric oxide prostaglandin E-2 and prostacyclin into the circulation. We investigated whether pGz may be effective as an early preconditioning strategy when applied one hour prior to whole body ischemia reperfusion injury induced by ventricular fibrillation (VF).

MAIN METHODS

Twenty anesthetized and paralyzed male swine were randomized to one hour of pGz and conventional mechanical ventilation [PC] or solely conventional mechanical ventilation [Control] prior to VF and resuscitation. After eight minutes of unsupported VF, cardiopulmonary resuscitation was carried out followed by defibrillation. Hemodynamics, electrocardiogram, echocardiogram, regional blood flows, and markers of global myocardial injury were measured. Protein expression of endothelial-derived nitric oxide synthase (eNOS), phosphorylated eNOS (p-eNOS), serine/threonine kinase Akt total (t-Akt), and phosphorylated (p-Akt) were determined by immunoblotting.

KEY FINDINGS

All animals had spontaneous return of circulation after cardiopulmonary resuscitation (CPR) and defibrillation. Preconditioned animals had less hemodynamically significant arrhythmias, less myocardial stunning, and greater regional blood flows to the brain, heart, kidneys, and ileum than Controls. Troponin I and creatine phosphokinase values in PC were 65% of the values present in Controls. In addition, preconditioned animals had higher protein expression of cardiac eNOS, p-eNOS, t-Akt, and p-Akt than Controls.

SIGNIFICANCE

pGz preconditioning confers early cardioprotection in a model of whole body ischemia reperfusion injury.

Delayed anti-arrhythmic effect of nitroglycerin in anesthetized rats: involvement of CGRP, PKC and mK ATP channels

Delayed anti-infarct and anti-stunning effects of nitroglycerin (NTG) have well been established in some animal models. The main goals of this study in anesthetized rats were to determine whether NTG has a delayed anti-arrhythmic effect and if so, whether calcitonin gene-related peptide (CGRP), protein kinase C (PKC) and mitochondrial K(ATP) channels (mK(ATP)) are involved in triggering this response. For this purpose, on day 0, male Wistar rats received NTG (120 microg/kg, iv) with or without pre-administration of PKC inhibitor chelerythrine (CHE), capsaicin (CAP) to deplete CGRP from sensory nerves or mK(ATP) channel blocker 5-hydroxydecaonic acid (5HD). On day 1, their hearts were subjected to 30 min ischemia and 120 min reperfusion. In rats pretreated with NTG, the incidence of ventricular tachycardia and ventricular fibrillation and the mortality rate significantly reduced (from 100%, 61% and 18.1% in the control group to 45.4%, 10% and 0% in the NTG group, respectively). Infarct size also reduced from 58+/-4.7% in the control group to 31+/-3.7% in the NTG group. These effects were abolished by CHE, CAP and 5HD, which none of them alone had any effect on infarct size or the incidence of myocardial arrhythmias. These results show that a low dose of NTG has a delayed anti-arrhythmic effect and this effect may share a common mechanism with anti-infarct effects of this drug, involving CGRP release and PKC and mK(ATP) activation.