Protective effects of ranolazine and propranolol, alone or combined, on the structural and functional alterations of cardiomyocyte mitochondria in a pig model of ischemia/reperfusion.

Preventing the consequences of ischemia/reperfusion (I/R)-induced lesions in the clinic requires the administration of pharmacological agents prior to restoring coronary vascularization. The aim of this study was to evaluate the effects of ranolazine and propranolol when administered either alone or combined prior to I/R induction in a pig model. Thirty domestic pigs were randomly assigned to five groups of six animals including (i) sham animals; (ii) untreated animals with 45-min ischemia and 1-min reperfusion; animals administered intravenously with (iii) ranolazine, or (iv) propranolol, or (v) both combined, prior to 45-min ischemia and 1-min reperfusion. The heart rate (HR), duration of monophasic action potentials (dMAP), and peak of the time derivative of left ventricular pressure (LV dP/dt max) were measured during ischemia and after 1 min of reperfusion. Structural and functional parameters of mitochondria were analyzed in tissue samples taken from the left ventricle ischemic area at the end of the experiment. I/R induced expected effects, namely accelerated HR, decreased dMAP and LV dP/dt max, and altered mitochondrial structural and functional parameters including decreased oxygen consumption, increased reactive oxygen species (ROS) production, and reduced calcium retention capacity resulting in the opening of mitochondrial permeability transition pores (mPTP). Ranolazine and propranolol administered either alone or combined prior to I/R significantly decreased all of these deleterious consequences. The protective effects of ranolazine and propranolol are seemingly due to the prevention of calcium overload and resulting lesions in mitochondria.

Ivabradine but not propranolol delays the time to onset of ischaemia-induced ventricular fibrillation by preserving myocardial metabolic energy status.

OBJECTIVE: Heart rate reduction (HRR) has shown a beneficial impact on the prevention of ventricular fibrillation, which could be explained by increased myocardial blood flow and preservation of mitochondrial structure. Here, we assessed the HRR impact on time to onset of ventricular fibrillation (TOVF) and myocardial metabolic energy status. METHODS AND RESULTS: An acute myocardial ischaemia was induced in pigs until ventricular fibrillation onset and TOVF was then measured. High-energy phosphates were measured in ventricular samples from the ischaemic region by nuclear magnetic resonance. Saline, ivabradine (IVA, a selective heart rate-lowering agent) and propranolol (PROPRA, a ß-blocker) were administered intravenously, 30 and 60 min respectively prior to ischaemia to ensure stable HRR. To study specifically the HRR impact, another set of animals received IVA and was submitted to rapid atrial pacing (200 bpm) to abolish HRR. IVA and PROPRA induced a similar HRR (IVA: 22-26%, PRORA: 20-21%, p<0.01 vs. control), which was associated with a significant increase in TOVF with IVA (2325s) compared to PROPRA (682s) and saline (401s). This effect was abolished by atrial pacing performed during ischaemia and throughout the entire experimental session. Only IVA partially prevented the decrease in phosphocreatine-to-ATP ratio (CrP/ATP) ratio and the ADP accumulation at the onset of ventricular fibrillation. Finally, CrP/ATP ratio levels were correlated with TOVF (r=0.74, p<0.001). CONCLUSION: Unlike PROPRA, IVA delayed the time to onset of ischaemia-induced ventricular fibrillation by preserving myocardial energy status, supporting the pertinence of IVA in the management of patients with coronary artery disease.