Blockade of Melatonin Receptors Abolishes Its Antiarrhythmic Effect and Slows Ventricular Conduction in Rat Hearts.

Melatonin has been reported to cause myocardial electrophysiological changes and prevent ventricular tachycardia or fibrillation (VT/VF) in ischemia and reperfusion. We sought to identify electrophysiological targets responsible for the melatonin antiarrhythmic action and to explore whether melatonin receptor-dependent pathways or its antioxidative properties are essential for these effects. Ischemia was induced in anesthetized rats given a placebo, melatonin, and/or luzindole (MT1/MT2 melatonin receptor blocker), and epicardial mapping with reperfusion VT/VFs assessment was performed. The oxidative stress assessment and Western blotting analysis were performed in the explanted hearts. Transmembrane potentials and ionic currents were recorded in cardiomyocytes with melatonin and/or luzindole application. Melatonin reduced reperfusion VT/VF incidence associated with local activation time in logistic regression analysis. Melatonin prevented ischemia-related conduction slowing and did not change the total connexin43 (Cx43) level or oxidative stress markers, but it increased the content of a phosphorylated Cx43 variant (P-Cx43368). Luzindole abolished the melatonin antiarrhythmic effect, slowed conduction, decreased total Cx43, protein kinase Cε and P-Cx43368 levels, and the IK1 current, and caused resting membrane potential (RMP) depolarization. Neither melatonin nor luzindole modified INa current. Thus, the antiarrhythmic effect of melatonin was mediated by the receptor-dependent enhancement of impulse conduction, which was associated with Cx43 phosphorylation and maintaining the RMP level.

Changes in Left Ventricular Ejection Fraction and Oxidative Stress after Phosphodiesterase Type-5 Inhibitor Treatment in an Experimental Model of Retrograde Rat Perfusion.

Background and objectives: Taking into consideration the confirmed role of oxidative stress in ischemia/reperfusion injury and the insufficiency in knowledge regarding the phosphodiesterase 5 (PDE5)-mediated effects on the cardiovascular system, the aim of our study was to investigate the influence of two PDE5 inhibitors, tadalafil and vardenafil, with or without the addition of N(G)-nitro-L-arginine methyl ester (L-NAME), on oxidative stress markers, coronary flow and left ventricular function, both ex vivo and in vivo. Methods: This study included 74 male Wistar albino rats divided into two groups. In the first, 24 male Wistar rats were orally treated with tadalafil or vardenafil for four weeks in order to perform in vivo experiments. In the second, the hearts of 50 male Wistar albino were excised and perfused according to the Langendorff technique in order to perform ex vivo experiments. The hearts were perfused with tadalafil (10, 20, 50 and 200 nM), vardenafil (10, 20, 50 and 200 nM) and a combination of tadalafil/vardenafil and L-NAME (30 µM). The CF and oxidative stress markers, including nitrite bioaviability (NO2-), superoxide anion radical (O2-), and the index of lipid peroxidation, were measured in coronary effluent. Results: The L-arginin/NO system acts as the mediator in the tadalafil-induced effects on the cardiovascular system, while it seems that the vardenafil-induced increase in CF was not primarily induced by the NO system. Although tadalafil induced an increase in O2- in the two lowest doses, the general effects of both of the applied PDE5 inhibitors on oxidative stress were not significant. The ejection function was above 50% in both groups. Conclusions: Our results showed that both tadalafil and vardenafil improved the coronary perfusion of the myocardium and LV function by increasing the EF.

Alkyl esters of 7-hydroxycoumarin-3-carboxylic acid as potent tissue-specific uncouplers of oxidative phosphorylation: Involvement of ATP/ADP translocase in mitochondrial uncoupling.

An impressive body of evidence has been accumulated now on sound beneficial effects of mitochondrial uncouplers in struggling with the most dangerous pathologies such as cancer, infective diseases, neurodegeneration and obesity. To increase their efficacy while gaining further insight in the mechanism of the uncoupling action has been remaining a challenge. Encouraged by our previous promising results on lipophilic derivatives of 7-hydroxycoumarin-4-acetic acid (UB-4 esters), here, we use a 7-hydroxycoumarin-3-carboxylic acid scaffold to synthesize a new series of 7-hydroxycoumarin (umbelliferone, UB)-derived uncouplers of oxidative phosphorylation - alkyl esters of umbelliferone-3-carboxylic acid (UB-3 esters) with varying carbon chain length. Compared to the UB-4 derivatives, UB-3 esters proved to be stronger uncouplers: the most effective of them caused a pronounced increase in the respiration rate of isolated rat heart mitochondria (RHM) at submicromolar concentrations. Both of these series of UB derivatives exhibited a striking difference between their uncoupling patterns in mitochondria isolated from liver and heart or kidney, namely: a pronounced but transient decrease in membrane potential, followed by its recovery, was observed after the addition of these compounds to isolated rat liver mitochondria (RLM), while the depolarization of RHM and rat kidney mitochondria (RKM) was rather stable under the same conditions. Interestingly, partial reversal of this depolarization in RHM and RKM was caused by carboxyatractyloside, an inhibitor of ATP/ADP translocase, thereby pointing to the involvement of this mitochondrial membrane protein in the uncoupling activity of both UB-3 and UB-4 esters. The fast membrane potential recovery in RLM uncoupled by the addition of the UB esters was apparently associated with hydrolysis of these compounds, catalyzed by mitochondrial aldehyde dehydrogenase (ALDH2), being in high abundance in liver compared to other tissues. Protonophoric properties of the UB derivatives in isolated mitochondria were confirmed by measurements of RHM swelling in the presence of potassium acetate. In model bilayer lipid membranes (liposomes), proton-carrying activity of UB-3 esters was demonstrated by measuring fluorescence response of the pH-dependent dye pyranine. Electrophysiological experiments on identified neurons from Lymnaea stagnalis demonstrated low neurotoxicity of UB-3 esters. Resazurin-based cell viability assay showed low toxicity of UB-3 esters to HEK293 cells and primary human fibroblasts. Thus, the present results enable us to consider UB-3 esters as effective tissue-specific protonophoric mitochondrial uncouplers.

Dose-dependent effects of perfluorocarbon-based blood substitute on cardiac function in myocardial ischemia-reperfusion injury.

The main goal of this study was to investigate the cardioprotective properties in terms of effects on cardiodynamics of perfluorocarbon emulsion (PFE) in ex vivo-induced ischemia-reperfusion injury of an isolated rat heart. The first part of the study aimed to determine the dose of 10% perfluoroemulsion (PFE) that would show the best cardioprotective effect in rats on ex vivo-induced ischemia-reperfusion injury of an isolated rat heart. Depending on whether the animals received saline or PFE, the animals were divided into a control or experimental group. They were also grouped depending on the applied dose (8, 12, 16 ml/kg body weight) of saline or PFE. We observed the huge changes in almost all parameters in the PFE groups in comparison with IR group without any pre-treatment. Calculated in percent, dp/dt max was the most changed parameter in group treated with 8 mg/kg, while the dp/dt min, SLVP, DLVP, HR, and CF were the most changed in group treated with 16 mg/kg 10 h before ischemia. The effects of 10% PFE are more pronounced if there is a longer period of time from application to ischemia, i.e., immediate application of PFE before ischemia (1 h) gave the weakest effects on the change of cardiodynamics of isolated rat heart. Therefore, the future of PFE use is in new indications and application methods, and PFE can also be referred to as antihypoxic and antiischemic blood substitute with mild membranotropic effects.

Chronic magnesium deficiency causes reversible mitochondrial permeability transition pore opening and impairs hypoxia tolerance in the rat heart.

Chronic magnesium (Mg) deficiency induces and exacerbates various cardiovascular diseases. We previously investigated the mechanisms underlying decline in cardiac function caused by chronic Mg deficiency and the effectiveness of Mg supplementation on this decline using the Langendorff-perfused isolated mouse heart model. Herein, we used the Langendorff-perfused isolated rat heart model to demonstrate the chronic Mg-deficient rats (Mg-deficient group) had lower the heart rate (HR) and left ventricular pressure (LVDP) than rats with normal Mg levels (normal group). Furthermore, decline in cardiac function due to hypoxia/reoxygenation injury was significantly greater in the Mg-deficient group than in the normal group. Experiments on mitochondrial permeability transition pore (mPTP) using isolated mitochondria revealed that mitochondrial membrane was fragile in the Mg-deficient group, implying that cardiac function decline through hypoxia/reoxygenation injury is associated with mitochondrial function. Mg supplementation for chronic Mg-deficient rats not only improved hypomagnesemia but also almost completely restored cardiac and mitochondrial functions. Therefore, proactive Mg supplementation in pathological conditions induced by Mg deficiency or for those at risk of developing hypomagnesemia may suppress the development and exacerbation of certain disease states.

[Features of innervation of epicardial adipose tissue in rats during aging (immunohistochemical study).]

The purpose of the article is to study the structure, innervation and state of the epicardial adipose tissue of the aortic-pulmonary region of the heart of rats at the age of 3-4 months and 18-23 months using neuroimmunohistochemical markers. Using a complex of histological and immunohistochemical methods, various nervous apparatus (ganglia, clusters of chromaffin cells, nerve trunks, nerve fibers, nerve plexuses, synaptic endings) with different mediators were identified in the white and brown adipose tissue of the base of the rat heart. It was found that parasympathetic and sympathetic postganglionic nerve fibers are involved in the innervation of white and brown adipose tissue. They penetrate into adipose tissue as part of Remak's cords of varicose axons along arterial vessels, form terminal synaptic plexuses of the en passant type, and are involved in the innervation of adipocytes of both types of epicardial adipose tissue. It was found that PGP 9.5+ cholinergic terminal nerve fibers predominate over catecholaminergic ones. During aging of rats, neurodegenerative, involutive (desimatization), and destructive pathological changes in white adipocytes were noted in epicardial adipose tissue.

St. Thomas Modified Cardioplegia Effects on Myoblasts' Viability and Morphology.

Background and Objectives: The cardioplegic arrest of the heart during cardiosurgical procedures is the crucial element of a cardioprotection strategy. Numerous clinical trials compare different cardioplegic solutions and cardioprotective protocols, but a relatively small number of papers apply to in vitro conditions using cultured cells. This work aimed to analyze whether it is possible to use the rat heart myocardium cells as an in vitro model to study the protective properties of St. Thomas cardioplegia (ST2C). Methods: The rat heart myocardium cells-H9C2 were incubated with cold cardioplegia for up to 24 h. After incubation, we determined: viability, confluency, and cell size, the thiol groups' level by modifying Ellman's method, Ki67, and Proliferating Cell Nuclear Antigen expression (PCNA). The impact on cells' morphology was visualized by the ultrastructural (TEM) study and holotomograpic 3D imaging. Results: The viability and confluency analysis demonstrated that the safest exposure to ST2C, should not exceed 4h. An increased expression of Ki67 antigen and PCNA was observed. TEM and 3D imaging studies revealed vacuolization after the longest period of exposure (24). Conclusions: According to obtained results, we conclude that STC can play a protective role in cardiac surgery during heart arrest.

Cytosolic, but not matrix, calcium is essential for adjustment of mitochondrial pyruvate supply.

Mitochondrial oxidative phosphorylation (OXPHOS) and cellular workload are tightly balanced by the key cellular regulator, calcium (Ca2+). Current models assume that cytosolic Ca2+ regulates workload and that mitochondrial Ca2+ uptake precedes activation of matrix dehydrogenases, thereby matching OXPHOS substrate supply to ATP demand. Surprisingly, knockout (KO) of the mitochondrial Ca2+ uniporter (MCU) in mice results in only minimal phenotypic changes and does not alter OXPHOS. This implies that adaptive activation of mitochondrial dehydrogenases by intramitochondrial Ca2+ cannot be the exclusive mechanism for OXPHOS control. We hypothesized that cytosolic Ca2+, but not mitochondrial matrix Ca2+, may adapt OXPHOS to workload by adjusting the rate of pyruvate supply from the cytosol to the mitochondria. Here, we studied the role of malate-aspartate shuttle (MAS)-dependent substrate supply in OXPHOS responses to changing Ca2+ concentrations in isolated brain and heart mitochondria, synaptosomes, fibroblasts, and thymocytes from WT and MCU KO mice and the isolated working rat heart. Our results indicate that extramitochondrial Ca2+ controls up to 85% of maximal pyruvate-driven OXPHOS rates, mediated by the activity of the complete MAS, and that intramitochondrial Ca2+ accounts for the remaining 15%. Of note, the complete MAS, as applied here, included besides its classical NADH oxidation reaction the generation of cytosolic pyruvate. Part of this largely neglected mechanism has previously been described as the "mitochondrial gas pedal." Its implementation into OXPHOS control models integrates seemingly contradictory results and warrants a critical reappraisal of metabolic control mechanisms in health and disease.

Cardiac, biochemical and histopathological analysis reveals impaired heart function in hypertensive rats with apical periodontitis.

AIM: To investigate the association between experimentally induced apical periodontitis (AP) and heart function in hypertensive rats. METHODOLOGY: Forty-eight normotensive Wistar albino and spontaneously hypertensive (SHR) rats were divided into four equal groups: control (C), normotensive with AP (AP), SHR and SHR with AP (SHR + AP). AP was induced on the first right mandibular molars by exposing the pulp chambers to the oral environment for four weeks and confirmed radiographically. Thereafter, the animals were sacrificed by cervical dislocation, whilst hearts were isolated and perfused according to the Langendorff technique gradually increasing coronary perfusion pressures 40-120 cmH2 O. The hemimandibles were analysed radiographically (mm2 and pixels) to verify the presence of AP. Biomarkers of cardiac oxidative stress (OS) were determined in coronary venous effluent and cardiac tissue homogenate. Cardiac tissue was analysed histopathologically for signs of heart damage (oedema, fibrosis and necrosis). All data were analysed by Kruskal-Wallis and one-way anova tests (p < .05). RESULTS: The levels of the maximum left ventricular pressure development rate of the SHR + AP group were significantly increased compared to the AP and C groups, and of the SHR group compared with the C group (p < .05). The levels of the minimum left ventricular pressure development rate of the SHR + AP group were significantly decreased compared to the AP, SHR and C groups, and of the SHR group compared to the C group (p < .05). The radiographic AP area was significantly larger in the SHR + AP group than in the AP group (p < .01). The levels of superoxide anion were significantly higher in the SHR + AP group than in the AP, SHR and C groups (p < .05). The activities of superoxide dismutase in cardiac tissue homogenate were significantly lower in the SHR + AP and AP groups compared with the SHR and C groups (p < .05). CONCLUSIONS: In rats, AP was associated with impaired cardiodynamics, disturbed cardiac OS, antioxidant defence and cardiac pathologic changes in hypertensive conditions. Hypertension was associated with an increase in the AP radiographic area. Further studies should confirm whether root canal treatment can have a cardioprotective effect and reduce cardiac OS in hypertensive conditions.

Flaxseed and evening primrose oil slightly affect systolic and diastolic function of isolated heart in male but not in female rats.

Considering that sex related differences in cardiac response to flaxseed (FSO) and evening primrose oil (EPO) are insufficiently known present investigation assessed the effect of these two oils, on the cardiac function of isolated rat hearts and the possible role of sex in this. The present study was carried out on 60 adult male Wistar albino rats randomly divided into 6 groups: male rats treated with EPO, dose of 10 mg/kg/day; female rats treated with EPO, dose of 10 mg/kg/day; male rats treated with FSO, dose of 300 mg/kg/day; female rats treated with FSO, dose of 300 mg/kg/day; control group of female rats treated with regular laboratory diet for animals; control group of male rats treated with regular laboratory diet for animals. Using the Langendorff technique, markers of the heart function were evaluated: the maximum and minimum rates of pressure development in the left ventricle (LV; dP/dtmax, dP/dtmin), systolic and diastolic left ventricular pressure (SLVP, DLVP, respectively), heart rate (HR) and coronary flow (CF). Male rats treated with EPO had significantly higher (p = 0.016) mean values of dP/dtmax, dP/dtmin, SLVP and DLVP (average increase for all CPPs 20%, 25%, 30% and 110%, respectively), compared to the group of male rats treated with FSO (p = 0.914). Our study results indicate that both types of PUFA oils only slightly changed the function of the isolated rat heart in male but not in female rats. Nevertheless, the difference between oil treatments was found in male rats who had stronger cardiac response after supplementation with EPO.

Subcellular Localization of Connexin 26 in Cardiomyocytes and in Cardiomyocyte-Derived Extracellular Vesicles.

Connexins (Cxs) are a family of membrane-spanning proteins, expressed in vertebrates and named according to their molecular weight. They are involved in tissue homeostasis, and they function by acting at several communication levels. Cardiac Cxs are responsible for regular heart function and, among them, Cx26 and Cx43 are widely expressed throughout the heart. Cx26 is present in vessels, as well as in cardiomyocytes, and its localization is scattered all over the cell aside from at the intercalated discs as is the case for the other cardiac Cxs. However, having been found in cardiomyocytes only recently, both its subcellular localization and its functional characterization in cardiomyocytes remain poorly understood. Therefore, in this study we aimed to obtain further data on the localization of Cx26 at the subcellular level. Our TEM immunogold analyses were performed on rat heart ventricles and differentiated H9c2 cardiac cell sections as well as on differentiated H9c2 derived extracellular vesicles. The results confirmed the absence of Cx26 at intercalated discs and showed the presence of Cx26 at the level of different subcellular compartments. The peculiar localization at the level of extracellular vesicles suggested a specific role for cardiac Cx26 in inter-cellular communication in an independent gap junction manner.

[Morphological signs of neurogenic inflammation in the heart of rats during aging.]

Using histological methods of staining with toluidine blue, hematoxylin-eosin and immunohistochemical reactions for the PGP 9,5 protein, tyrosine hydroxylase (TH), Iba-1 protein, cellular changes in different parts of the heart of Wistar rats at the age of 18-23 months were studied. In the connective tissue of the heart base, focal inflammatory infiltrates were found, near which PGP 9.5+ and TH+ plexuses, consisting of parasympathetic and sympathetic nerve fibers, were detected. In the area of the valvular heart apparatus, at the border of the anneau fibreux and the myocardium of the right atrium, pathological changes in nerve structures were found: degeneration of nerve fibers and granular destruction varicose axons of the terminal plexus. A close relationship has been established between axons of the terminal nervous network and cells of inflammatory infiltrates and blood capillaries. The features of the localization of neurocellular inflammatory complexes consisting of nerve fibers, blood capillaries and cells participating in the local inflammatory process (mast cells, histiocytes, monocytes, fibroblasts, plasma cells) in various parts of the myocardium in old animals are described. The chronic nature of neurogenic inflammation in the heart during aging has been established.

[Effects of ultrafine particulates on cardiac function in rat isolated heart].

OBJECTIVE: To evaluate whether ultrafine particulates (UFPs) have direct deleterious effects on cardiac function through activating MAPK signaling. METHODS: Langendorff-perfused Sprague-Dawley rat hearts were randomly divided into 2 groups (n=10/each group). In control group, the rat hearts were perfused with Tyrode's buffer for 40 min; in UFPs-treated group, the hearts were perfused with UFPs at a concentration of 12.5 mg/L. Cardiac function was determined by measuring left ventricular developed pressure (LVDP), left ventricular peak rate of contraction and relaxation (±dp/dtmax) and coronary flow (CF). The levels of malondialdehyde (MDA), superoxide dismutase (SOD), total anti-oxidant capacity (TAOC) were detected in order to evaluate cardiac oxidative stress via the thiobarbituric acid assay, water soluble tetrazolium salt assay and colorimetry, respectively. The expressions of p-p38 MAPK, p-ERKs and p-JNKs in the myocardium were observed using immunohistochemical staining and Western blots. RESULTS: No significant changes in cardiac function were detected before and after the perfusion in control group while UFPs perfused hearts showed a decline in cardiac function in a time-dependent manner (all P < 0.05). In UFPs-treated group, LVDP, +dp/dtmax, -dp/dtmax and CF were statistically reduced from (82.6±2.1) mmHg, (1 624±113) mmHg/s, (1 565±116) mmHg/s, (12.0±0.2) mL/min to (56.8±4.4) mmHg, (1 066±177) mmHg/s, (1 082±134) mmHg/s, (8.7±0.3) mL/min (all P < 0.05), respectively. Furthermore, The comparison between the two groups observed that UFPs perfusion caused a significant decrease in cardiac function at 30 and 40 min compared with the control group (all P < 0.05). At the end of the perfusion, the level of MDA was increased from (0.98±0.14) nmol/L to (1.95±0.18) nmol/L, while SOD and TAOC were reduced from (12.50±1.87) U/mL and (6.83±1.16) U/mL to (6.50 ±1.04) U/mL and (3.67±0.82) U/mL (all P < 0.001) in UFPs group, respectively. In coincidence with these changes, immunohistochemistry and Western blots results showed that the levels of p-p38 MAPK, p-ERKs and p-JNKs in the myocardium significantly increased in UFPs group as compared with control group (all P < 0.05). CONCLUSION: The results of this study demonstrated that the short-term exposure of UFPs to the isolated rat hearts has direct and acute toxic effects on cardiac function, probably related to attenuation of anti-oxidative capacity and activation of MAPK signaling pathways.

Garlic Derived Diallyl Trisulfide in Experimental Metabolic Syndrome: Metabolic Effects and Cardioprotective Role.

This study aimed to examine the effects of diallyl trisulfide (DATS), the most potent polysulfide derived from garlic, on metabolic syndrome and myocardial function in rats with metabolic syndrome (MetS). For that purpose, we used 36 male Wistar albino rats divided into control rats, rats with MetS and MetS rats treated with 40 mg/kg of DATS every second day for 3 weeks. In the first part, we studied the impact of DATS on MetS control and found that DATS significantly raised H2S, decreased homocysteine and glucose levels and enhanced lipid and antioxidative, while reducing prooxidative parameters. Additionally, this polysulfide improved cardiac function. In the second part, we investigated the impact of DATS on ex vivo induced ischemia/reperfusion (I/R) heart injury and found that DATS consumption significantly improved cardiodynamic parameters and prevented oxidative and histo-architectural variation in the heart. In addition, DATS significantly increased relative gene expression of eNOS, SOD-1 and -2, Bcl-2 and decreased relative gene expression of NF-κB, IL-17A, Bax, and caspases-3 and -9. Taken together, the data show that DATS can effectively mitigate MetS and have protective effects against ex vivo induced myocardial I/R injury in MetS rat.

Protective efficacy of dinitrosyl iron complexes with reduced glutathione in cardioplegia and reperfusion.

Disturbed homeostasis of nitric oxide (NO) is one of the causes of myocardial ischemia/reperfusion (I/R) injury during open-heart surgery. This study was designed to explore mechanisms of action of dinitrosyl iron complexes with reduced glutathione ({(GS-)2Fe+(NO+)2}+, DNIC-GS) added to crystalloid cardioplegia or reperfusion solution in isolated working rat hearts. Hearts of male Wistar rats were subjected to cardioplegic arrest by St. Thomas' Hospital cardioplegic solution (STH) and normothermic global ischemia followed by reperfusion. DNIC-GS were used with STH or during early reperfusion. Lactate dehydrogenase (LDH) activity in the coronary effluent and myocardial contents of adenine nucleotides, phosphocreatine, and lactate were determined spectrophotometrically. Reactive oxygen species (ROS) formation in the coronary effluent and myocardial DNIC content was assessed by EPR technique. Cardioplegia or reperfusion with DNIC-GS significantly improved recovery of coronary flow and cardiac function compared with control. Carboxy-[2-(4-carboxyphenyl)-4,4,5,5-tetramethyl-imidozoline-1-oxy-3-oxide] (C-PTIO), a selective NO scavenger, reduced/abolished protective action of DNIC-GS. Enhanced recovery of cardiac function with DNIC-GS reduced LDH release in the coronary effluent, augmented recovery of myocardial energy state, and decreased formation of ROS-generating systems at reperfusion. Beneficial effects of DNIC-GS were related to the transfer of [Fe(NO)2] cores to thiol groups of myocardial proteins to form intracellular DNIC pools. The study concluded that DNIC-GS is a promising adjunct agent for metabolic and antioxidant protection of the heart during cardioplegic arrest and reperfusion.

Surgical and physiological challenges in the development of left and right heart failure in rat models.

Rodent surgical animal models of heart failure (HF) are critically important for understanding the proof of principle of the cellular alterations underlying the development of the disease as well as evaluating therapeutics. Robust, reproducible rodent models are a prerequisite to the development of pharmacological and molecular strategies for the treatment of HF in patients. Due to the absence of standardized guidelines regarding surgical technique and clear criteria for HF progression in rats, objectivity is compromised. Scientific publications in rats rarely fully disclose the actual surgical details, and technical and physiological challenges. This lack of reporting is one of the main reasons that the outcomes specified in similar studies are highly variable and associated with unnecessary loss of animals, compromising scientific assessment. This review details rat circulatory and coronary arteries anatomy, the surgical details of rat models that recreate the HF phenotype of myocardial infarction, ischemia/reperfusion, left and right ventricular pressure, and volume overload states, and summarizes the technical and physiological challenges of creating HF. The purpose of this article is to help investigators understand the underlying issues of current HF models in order to reduce variable results and ensure successful, reproducible models of HF.

Heart defibrillation: relationship between pacing threshold and defibrillation probability.

BACKGROUND: Considering the clinical importance of the ventricular fibrillation and that the most used therapy to reverse it has a critical side effect on the cardiac tissue, it is desirable to optimize defibrillation parameters to increase its efficiency. In this study, we investigated the influence of stimuli duration on the relationship between pacing threshold and defibrillation probability. RESULTS: We found out that 0.5-ms-long pulses had a lower ratio of defibrillation probability to the pacing threshold, although the higher the pulse duration the lower is the electric field intensity required to defibrillate the hearts. CONCLUSION: The appropriate choice of defibrillatory shock parameters is able to increase the efficiency of the defibrillation improving the survival chances after the occurrence of a severe arrhythmia. The relationship between pulse duration and the probability of reversal of fibrillation shows that this parameter cannot be underestimated in defibrillator design since different pulse durations have different levels of safety.

The impact of high-intensity interval training and moderate-intensity continuous training regimes on cardiodynamic parameters in isolated heart of normotensive and hypertensive rats.

This study aimed to assess the impact of high-intensity interval training (HIIT) vs. moderate-intensity continuous training (MIT) on cardiodynamic parameters in isolated rat heart. Wistar albino rats were randomly assigned to groups according to running protocol: sedentary control, MIT, and HIIT; spontaneous hypertensive rat (SHR) sedentary control, SHR + MIT, and SHR + HIIT. HIIT groups performed the running in 5 sprints × 45-55 m/min for 30-90 s, with 2 min of rest after each sprint, while MIT groups performed the running of 10-15 m/min for 1 h with 3 min of rest every 100 m; both protocols were implemented 5 days/week over 4 weeks with 1 week of adaptation before protocols started. Isolated rat hearts were perfused according to Langendorff technique at gradually increased coronary perfusion pressures (40-120 cmH2O). Using a sensor placed in the left ventricle, we registered maximum and minimum rate of pressure development in the left ventricle, systolic and diastolic left ventricular pressure, and heart rate. Coronary flow was measured flowmetrically. MIT was connected with cardiac depression in normotensive conditions, while HIIT leads to cardiac depression in hypertensive rats. HIIT induced more significant increase of contractile and relaxation parameters of the isolated rat heart, especially in hypertensive animals.

Cisplatin and cisplatin analogues perfusion through isolated rat heart: the effects of acute application on oxidative stress biomarkers.

Drug-induced oxidative stress can occur in numerous tissues and organ systems (liver, kidney, ear, nervous system, and cardiovascular system). Cancer therapy with cisplatin is associated with side effects to which oxidative stress may contribute. We have compared the influences of cisplatin (reference compound) and its' analogues (dichloro(1,2-diaminocyclohexane)platinum(II) and chloro(2,2':6',2″-terpyridine)platinum(II)) in a model of isolated rat heart using the Langendorff technique. The production of oxidative stress biomarkers, antioxidant enzymes, myocardial damage, and expression of Bax, OH-1, and SODs were studied. Cisplatin and the analogues were perfused at concentration of 10-6 and 10-5 M during 30 min. The results of this study showed that examined platinum complexes had different ability to induce oxidative stress of isolated perfused rat heart. Varying the carrier ligands, such as 1,2-diaminocyclohexane and 2,2':6',2″-terpyridine, related to amino ligands (cisplatin) directly influenced the strength to induce production of oxidative stress biomarkers. Introducing 2,2':6',2″-terpyridine ligands provoked the smallest changes in antioxidant enzymes activity, lipid peroxidation, and expression of heme oxygenase-1, that undoubtedly indicated that this complex had the lowest impact on redox status in heart tissue. These findings may be useful in synthesis of novel platinum analogues with lower potential for oxidative stress induction. However, the fact that platinum complexes could induce toxic effects in the heart by other mechanisms should be taken into the consideration.

Effects of homocysteine and its related compounds on oxygen consumption of the rat heart tissue homogenate: the role of different gasotransmitters.

The objective of this study was to investigate in vitro effects of 10 µM DL-homocysteine (DL-Hcy), DL-homocysteine thiolactone-hydrochloride (DL-Hcy TLHC), and L-homocysteine thiolactone-hydrochloride (L-Hcy TLHC) on the oxygen consumption of rat heart tissue homogenate, as well as the involvement of the gasotransmitters NO, H2S and CO in the effects of the most toxic homocysteine compound, DL-Hcy TLHC. The possible contribution of the gasotransmitters in these effects was estimated by using the appropriate inhibitors of their synthesis (N ω-nitro-L-arginine methyl ester (L-NAME), DL-propargylglycine (DL-PAG), and zinc protoporphyrin IX (ZnPPR IX), respectively). The oxygen consumption of rat heart tissue homogenate was measured by Clark/type oxygen electrode in the absence and presence of the investigated compounds. All three homocysteine-based compounds caused a similar decrease in the oxygen consumption rate compared to control: 15.19 ± 4.01%, 12.42 ± 1.01%, and 16.43 ± 4.52% for DL-Hcy, DL-Hcy TLHC, or L-Hcy TLHC, respectively. All applied inhibitors of gasotransmitter synthesis also decreased the oxygen consumption rate of tissue homogenate related to control: 13.53 ± 1.35% for L-NAME (30 µM), 5.32 ± 1.23% for DL-PAG (10 µM), and 5.56 ± 1.39% for ZnPPR IX (10 µM). Simultaneous effect of L-NAME (30 µM) or ZnPPR IX (10 µM) with DL-Hcy TLHC (10 µM) caused a larger decrease of oxygen consumption compared to each of the substances individually. However, when DL-PAG (10 µM) was applied together with DL-Hcy TLHC (10 µM), it attenuated the effect of DL-Hcy TLHC from 12.42 ± 1.01 to 9.22 ± 1.58%. In conclusion, cardiotoxicity induced by Hcy-related compounds, which was shown in our previous research, could result from the inhibition of the oxygen consumption, and might be mediated by the certain gasotransmitters.