Ventricular Developed Pressure Research Articles

Exercise Preconditioning Preserves Cardiac Function and Enhances Cardiac Recovery Following Dobutamine Stimulation in Doxorubicin-Treated Rat Hearts.

Exercise preconditioning has been shown to protect against doxorubicin (DOX)-induced cardiac dysfunction when hearts are maintained under resting conditions. However, it is unclear whether this exercise-induced protective effect is maintained when the heart is challenged with the β 1 -adrenergic receptor agonist dobutamine (DOB), which mimics acute exercise stress. Fischer 344 rats were randomly assigned to sedentary (SED) or voluntary wheel running (WR) groups for 10 weeks. At week 11, rats were treated with either 15 mg/kg DOX or saline. Five days later, ex vivo cardiac function was assessed using an isolated working heart model at baseline, during the infusion of 7.5 μg·kg -1 ·min -1 DOB, and during recovery. DOB infusion significantly increased left ventricular developed pressure (LVDP), maximal (dP/dt max ) and minimal (dP/dt min ) rate of left ventricular pressure development, and heart rate in all groups ( P < 0.05). SED + DOX also showed a lower baseline and recovery LVDP than WR + DOX (83 ± 12 vs. 109 ± 6 mm Hg baseline, 76 ± 11 vs. 100 ± 10 mm Hg recovery, P < 0.05). WR + DOX showed higher dP/dt max and lower dP/dt min when compared with SED + DOX during DOB infusion (7311 ± 1481 vs. 5167 ± 1436 mm Hg/s and -4059 ± 1114 vs.-3158 ± 1176 mm Hg/s, respectively). SED + DOX dP/dt max was significantly lower during baseline and during recovery when compared with all other groups ( P < 0.05). These data suggest that exercise preconditioning preserved cardiac function after DOX exposure even when the heart is challenged with DOB, and it appeared to preserve the heart's ability to recover from this functional challenge.

Discovery of a novel cardiac-specific myosin modulator using artificial intelligence-based virtual screening

Direct modulation of cardiac myosin function has emerged as a therapeutic target for both heart disease and heart failure. However, the development of myosin-based therapeutics has been hampered by the lack of targeted in vitro screening assays. In this study we use Artificial Intelligence-based virtual high throughput screening (vHTS) to identify novel small molecule effectors of human β-cardiac myosin. We test the top scoring compounds from vHTS in biochemical counter-screens and identify a novel chemical scaffold called ‘F10’ as a cardiac-specific low-micromolar myosin inhibitor. Biochemical and biophysical characterization in both isolated proteins and muscle fibers show that F10 stabilizes both the biochemical (i.e. super-relaxed state) and structural (i.e. interacting heads motif) OFF state of cardiac myosin, and reduces force and left ventricular pressure development in isolated myofilaments and Langendorff-perfused hearts, respectively. F10 is a tunable scaffold for the further development of a novel class of myosin modulators.

Dexmedetomidine Preconditioning Attenuates Myocardial Ischemia/Reperfusion Injury in Rats by Suppressing Mitophagy Via Activating Α2-Adrenergic Receptor.

Dexmedetomidine (DEX), a specific α2-adrenergic receptor agonist, is protective against myocardial ischemia/reperfusion injury (MIRI). However, the association between DEX preconditioning-induced cardioprotection and mitophagy suppression remains unclear. Hence, we aimed to investigate whether DEX preconditioning alleviates MIRI by suppressing mitophagy via α2-adrenergic receptor activation. Sixty isolated rat hearts were treated with or without DEX before inducing ischemia and reperfusion; an α2-adrenergic receptor antagonist, yohimbine (YOH), was also administered before ischemia, alone or with DEX. The heart rate (HR), left ventricular diastolic pressure (LVDP), left ventricular end-diastolic pressure (LVEDP), maximal and minimal rate of left ventricular pressure development (±dp/dtmax), and myocardial infarction size were measured. The mitochondrial ultrastructure and autophagosomes were assessed using transmission electron microscopy. Mitochondrial membrane potential and reactive oxygen species (ROS) levels were measured using JC-1 and dichloride hydrofluorescein diacetate assays, respectively. The expression levels of the mitophagy-associated proteins Beclin1, LC3II/I ratio, p62, PINK1, and Parkin were detected by western blotting. Compared with the control group, in the ischemia/reperfusion group, the HR, LVDP, and ±dp/dtmax were remarkably decreased (p< 0.05), whereas LVEDP and infarct sizes were significantly increased (p< 0.05). DEX preconditioning significantly improved cardiac dysfunction reduced myocardial infarction size, maintained mitochondrial structural integrity, increased mitochondrial membrane potential, inhibited autophagosomes formation, and decreased ROS production and Beclin1, LC3II/I ratio, PINK1, Parkin, and p62 expression(p< 0.05). When DEX and YOH were combined, YOH canceled the effect of DEX, whereas the use of YOH alone had no effect. Therefore, DEX preconditioning was cardioprotective against MIRI in rats by suppressing mitophagy via α2-adrenergic receptor activation.

Tricyclic hydrocarbon fluorene attenuates ventricular ionic currents and pressure development in the navaga cod

The release of polycyclic aromatic hydrocarbons (PAHs) into the environment due to oil and diesel fuel spills is a serious threat to Arctic fish populations. PAHs produce multiple toxic effects in fish, but disturbance of electrical and contractile activity of the heart seems to be the most negative effect. Our study focused on the effects of fluorene, a tricyclic PAH resembling the well-investigated tricyclic phenanthrene, on major ionic currents and action potential (AP) waveform in isolated ventricular myocytes and on contractile activity in isolated whole hearts of polar navaga cod (Eleginus nawaga). Among the studied currents, the repolarizing rapid delayed rectifier K+ current IKr demonstrated the highest sensitivity to fluorene with IC50 of 0.54 μM. The depolarizing inward currents, INa and ICaL, were inhibited with 10 μM fluorene by 20.2 ± 2.8 % and 27.9 ± 8.4 %, respectively, thereby being much less sensitive to fluorene than IKr. Inward rectifier IK1 current was insensitive to fluorene (up to 10 μM). While 3 μM fluorene prolonged APs, 10 μM also slowed the AP upstroke. Resting membrane potential was not affected by any tested concentrations. In isolated heart experiments 10 μM fluorene caused modest depression of ventricular contractile activity. Thus, we have demonstrated that fluorene, a tricyclic PAH present in high quantities in crude oil, strongly impacts electrical activity with only slight effects on contractile activity in the heart of the polar fish, the navaga cod.

Effects of dandelion root on rat heart function and oxidative status

This study aimed to examine the effects of dandelion root on rat heart function and oxidative status. At the beginning of the experimental protocol, Wistar albino rats were randomly classified into two groups (10 rats per group): 1. control group – animals that drank tap water; 2. experimental group – animals that drank dandelion root for four weeks. Every morning for four weeks, the animals received freshly boiled dandelion root in a volume of 250 ml. At the end of the dandelion administration, animals were sacrificed, and their hearts were isolated and retrogradely perfused according to the Langendorff technique at a gradually increasing perfusion pressure between 40 – 120 cm H2O. The following myocardial function parameters were measured: maximum rate of left ventricular pressure development (dp/dt max), minimum rate of left ventricular pressure development (dp/dt min), systolic left ventricular pressure (SLVP), diastolic left ventricular pressure (DLVP), heart rate (HR). In addition, the coronary flow (CF) was measured flowmetrically. Finally, blood samples were collected after sacrificing to determine oxidative stress biomarkers: nitrite (NO2−), superoxide anion radical (O2−), hydrogen peroxide (H2O2), the index of lipid peroxidation (TBARS), reduced glutathione (GSH), catalase (CAT) and superoxide dismutase (SOD). The present pioneer results indicated that dandelion root did not manifest a negative impact on functional aspects of isolated rat heart. In addition, dandelion consumption was not associated with promising results in terms of maintaining systemic redox balance.

N-terminal truncated cardiac troponin I enhances Frank-Starling response by increasing myofilament sensitivity to resting tension.

Cardiac troponin I (cTnI) of higher vertebrates has evolved with an N-terminal extension, of which deletion via restrictive proteolysis occurs as a compensatory adaptation in chronic heart failure to increase ventricular relaxation and stroke volume. Here, we demonstrate in a transgenic mouse model expressing solely N-terminal truncated cTnI (cTnI-ND) in the heart with deletion of the endogenous cTnI gene. Functional studies using ex vivo working hearts showed an extended Frank-Starling response to preload with reduced left ventricular end diastolic pressure. The enhanced Frank-Starling response effectively increases systolic ventricular pressure development and stroke volume. A novel finding is that cTnI-ND increases left ventricular relaxation velocity and stroke volume without increasing the end diastolic volume. Consistently, the optimal resting sarcomere length (SL) for maximum force development in cTnI-ND cardiac muscle was not different from wild-type (WT) control. Despite the removal of the protein kinase A (PKA) phosphorylation sites in cTnI, β-adrenergic stimulation remains effective on augmenting the enhanced Frank-Starling response of cTnI-ND hearts. Force-pCa relationship studies using skinned preparations found that while cTnI-ND cardiac muscle shows a resting SL-resting tension relationship similar to WT control, cTnI-ND significantly increases myofibril Ca2+ sensitivity to resting tension. The results demonstrate that restrictive N-terminal deletion of cTnI enhances Frank-Starling response by increasing myofilament sensitivity to resting tension rather than directly depending on SL. This novel function of cTnI regulation suggests a myofilament approach to utilizing Frank-Starling mechanism for the treatment of heart failure, especially diastolic failure where ventricular filling is limited.

Exercise Preconditioning Preserves Cardiac Function and Enhances Cardiac Recovery Following Dobutamine Stimulation in Doxorubicin‐Treated Rat Hearts

Doxorubicin (DOX) is a chemotherapeutic drug used to treat a wide range of cancers, and its use is limited by cardiotoxicity. Exercise preconditioning has been shown to protect against DOX‐induced cardiac dysfunction when hearts are maintained under resting conditions. However, it is unclear whether this exercise‐induced protective effect is maintained when the heart is challenged during an acute exercise bout. It was hypothesized that preconditioning protects the heart against DOX cardiotoxicity when it is challenged with the β1‐adrenergic receptor agonist dobutamine (DOB), which mimics acute exercise stress.Fischer 344 rats were randomly assigned to sedentary (SED) or voluntary wheel running (WR) groups for 10 weeks. At week 11, rats were treated with either 15 mg/kg DOX or saline (SAL). Five days later, ex vivo cardiac function was assessed using an isolating working heart model at baseline, during the infusion of 7.5 μg/kg/min DOB, and during recovery.DOB infusion significantly increased left ventricular developed pressure (LVDP), maximal (dP/dtmax) and minimal (dP/dtmin) rate of left ventricular pressure development, and heart rate in all groups (p&lt;0.05). During the recovery phase (i.e., after DOB washout) LVDP was significantly lower than baseline in all groups except for SED+DOX (baseline vs. recovery: SED+SAL: 97±2 vs. 84±5 mmHg; WR+SAL: 116±7 vs. 90±7 mmHg; SED+DOX: 83±5 vs. 76±4 mmHg; WR+DOX: 109+2 vs. 100±4 mmHg, p&lt;0.05). SED+DOX also showed a lower baseline and recovery LVDP than WR+DOX (83±5 vs. 109±2 mmHg baseline, 76±4 vs. 100±4 mmHg recovery, p&lt;0.05). WR+DOX showed higher dP/dtmax and lower dP/dtmin when compared to SED+DOX during DOB infusion (7311±605 vs. 5167±508 mmHg/s and ‐4059±454 vs. ‐3158±416 mmHg/s, respectively). SED+DOX dP/dtmax was significantly lower during DOB infusion and during recovery when compared to all other groups (p&lt;0.05). During DOB and recovery, +DOX groups showed lower HR values than +SAL groups (p&lt;0.05).These data demonstrate that exercise preconditioning preserved cardiac function after DOX exposure even when the heart is challenged, and it appeared to preserve the heart’s ability to recovery from this functional challenge. Cardioprotection seems to extend beyond rest into conditions which challenge cardiac function. These observations support the premise that exercise training can protect against cardiac dysfunction that may occur during acute exercise in cancer patients undergoing DOX treatment.

Teriflunomide treatment exacerbates cardiac ischemia reperfusion injury in isolated rat hearts.

PurposePrevious work suggests that Dihydroorotate dehydrogenase (DHODH) inhibition via teriflunomide (TERI) may provide protection in multiple disease models. To date, little is known about the effect of TERI on the heart. This study was performed to assess the potential effects of TERI on cardiac ischemia reperfusion injury.MethodsMale and female rat hearts were subjected to global ischemia (25 min) and reperfusion (120 min) on a Langendorff apparatus. Hearts were given either DMSO (VEH) or teriflunomide (TERI) for 5 min prior to induction of ischemia and during the reperfusion period. Left ventricular pressure, ECG, coronary flow, and infarct size were determined using established methods. Mitochondrial respiration was assessed via respirometry.ResultsPerfusion of hearts with TERI led to no acute effects in any values measured across 500 pM–50 nM doses. However, following ischemia–reperfusion injury, we found that 50 nM TERI-treated hearts had an increase in myocardial infarction (p < 0.001). In 50 nM TERI-treated hearts, we also observed a marked increase in the severity of contracture (p < 0.001) at an earlier time-point (p = 0.004), as well as reductions in coronary flow (p = 0.037), left ventricular pressure development (p = 0.025), and the rate-pressure product (p = 0.008). No differences in mitochondrial respiration were observed with 50 nM TERI treatment (p = 0.24–0.87).ConclusionThis study suggests that treatment with TERI leads to more negative outcomes following cardiac ischemia reperfusion, and administration of TERI to at-risk populations should receive special considerations.

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

To investigate the association between experimentally induced apical periodontitis (AP) and heart function in hypertensive rats. 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 40-120cmH2 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). 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). 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.

Liraglutide restores late cardioprotective effects of remote preconditioning in diabetic rats via activation of hydrogen sulfide and nuclear factor erythroid 2-related factor 2 signaling pathway.

ABSTRACTPurposeThe present study explored the influence of liraglutide on remote preconditioning-mediated cardioprotection in diabetes mellitus along with the role of nuclear factor erythroid 2-related factor 2 (Nrf2), hypoxia inducible factor (HIF-1α) and hydrogen sulfide (H2S).MethodsStreptozotocin was given to rats to induce diabetes mellitus and rats were kept for eight weeks. Four cycles of ischemia and reperfusion were given to hind limb to induce remote preconditioning. After 24 h, hearts were isolated and subjected to 30 min of ischemia and 120 min of reperfusion on Langendorff system. Liraglutide was administered along with remote preconditioning. Cardiac injury was assessed by measuring the release of creatine kinase (CK-MB), cardiac troponin (cTnT) and development of left ventricular developed pressure. After ischemia-reperfusion, hearts were homogenized to measure the nuclear cytoplasmic ratio of Nrf2, H2S and HIF-1α levels.ResultsIn diabetic rats, there was more pronounced injury and the cardioprotective effects of remote preconditioning were not observed. Administration of liraglutide restored the cardioprotective effects of remote preconditioning in a dose-dependent manner. Moreover, liraglutide increased the Nrf2, H2S and HIF-1α levels in remote preconditioning-subjected diabetic rats.ConclusionsLiraglutide restores the lost cardioprotective effects of remote preconditioning in diabetes by increasing the expression of Nrf2, H2S and HIF-1α.

The effect of hyperbaric oxygenation on cardiodynamics and oxidative stress in rats with sepsis

Background/Aim. Dysfunctions at the cellular, tissue, and organ level, which can result in death, are caused by metabolic changes and affection on the regulation of gene transcription and micro- and macrocirculation. The aim of the present study was to assess the impact of hyperbaric oxygenation (HBO) on isolated heart as well as on the oxidative status of rats with sepsis. Methods. The investigation included male Wistar albino rats classified into three groups: the first group was a control group (CTRL); the second group included animals exposed only to the induction of sepsis without HBO treatment (the Sepsis group), while the third group included animals treated with HBO after the induction of sepsis (the Sepsis + HBO group). For the induction of sepsis, fecal peritonitis model was used (3 mL/kg of fecal suspension administered intraperitoneally). After the induction of sepsis, the rats were exposed twice a day (on 12 hours) to HBO treatment at 2.8 atmospheres absolute (ATA) for 90 minutes over a period of 3 days. 72 h after the confirmation of sepsis, the animals were sacrificed and the hearts were retrogradely perfused on the Langendorff apparatus at a gradually increased coronary perfusion pressure (CPP = 40?120 cm H2O). The following parameters of heart function were continuously recorded: maximum and minimum rate of left ventricular pressure development (dp/dt max, dp/dt min); systolic and diastolic left ventricular pressure (SLVP and DLVP); heart rate (HR). Coronary flow (CF) was measured flowmetrically. Following oxidative stress markers were measured: nitrites (NO2?), superoxide anion radical (O2?), hydrogen peroxide (H2O2), index of lipid peroxidation (TBARS), activity of superoxide dismutase (SOD) and catalase (CAT) and the level of reduced glutathione (GSH). Results. There were no significant differences in dp/dt max, dp/dt min, SLVP and HR between the groups. CF was statistically significantly higher (p &lt; 0.01) in the sepsis group. The values of all cardiac oxidative markers were lower in the sepsis + HBO group (p &lt; 0.05), while systemic pro-oxidative and antioxidative parameters were unchanged. Conclusion. Our results showed that HBO treatment was not associated with improved cardiac function and coronary perfusion, while expressed promising beneficial effects on cardiac oxidative stress.

The influence of folic acid-induced acute kidney injury on cardiac function and redox status in rats.

The aim of this study was to evaluate the influence of acute kidney injury caused by high doses of folic acid on cardiac function and markers of oxidative stress in serum and isolated rat heart. Isolated hearts of Wistar albino rats (divided into two groups: control and folic acid group) were perfused according to Langendorff technique at basal coronary perfusion pressure CPP of 70cm H2O. After a stabilization period, CPP was lowered to 60cm H2O and then gradually increased to 80, 100, 120 and finally decreased to 40cm H2O in order to establish coronary autoregulation. For each perfusion pressure value, the left ventricular function parameters were determined. Samples of coronary venous effluent were collected for determination of coronary flow and biomarkers of oxidative stress. The blood samples were collected in order to examine the values of serum urea, creatinine, Na, K, and parameters of oxidative stress and antioxidant defense system. Heart and kidney tissue samples were collected for histopathological examination. Folic acid group showed reduction of systolic and diastolic left ventricular pressure and increase of coronary flow and minimum left ventricular pressure development rate. In coronary flow, folic acid group showed increased levels of TBARS and reduction of H2O2 and NO2-. Serum ROS concentrations were lower in rats treated with folic acid, particularly levels of TBARS and NO2- in which values were significantly lower. The parameters of systemic antioxidative stress were at significantly high levels especially SOD and GSH. This study is the experimental confirmation of cardio-renal syndrome type 3, which represents the acute kidney injury that causes a damage of a heart function. The data suggest that negative effects of acute kidney injury on myocardium do not necessarily involve oxidative stress, which may lead to future investigations which will be based on inflammation as a one of the important factors in the organ crosstalk.

Ischemia and reperfusion injury following cardioplegic arrest is attenuated by age and testosterone deficiency in male but not female mice

BackgroundCardiovascular disease increases with age in both sexes. Treatment can require cardiac surgery, where the hearts are pre-treated with protective cardioplegic solution before ischemia and reperfusion (I/R). While endogenous estrogen is beneficial in I/R, whether testosterone is involved is uncertain and whether age modifies responses to I/R is unclear. We investigated sex- and age-specific differences in I/R injury in the hearts pre-treated with clinically relevant cardioplegic solution.MethodsThe hearts were isolated from young (6–9 months) and old (20–28 months) mice of both sexes and perfused (Langendorff) with Krebs-Henseleit buffer (15 min, 37 °C), followed by St. Thomas’ two cardioplegia (6 min, 6–7 °C), global ischemia (90 min, 23–24 °C), and reperfusion (30 min, 37 °C). The hearts were perfused with triphenyltetrazolium chloride to quantify infarct area. Testosterone’s role was investigated in gonadectomized (GDX, 6–9 months) male mice; serum testosterone and estradiol were measured with ELISA assays.ResultsLeft ventricular developed pressure (LVDP) recovered to 67.3 ± 7.4% in the old compared to 21.8 ± 9.2% in the young male hearts (p < 0.05). Similar results were seen for rates of pressure development (+dP/dt) and decay (−dP/dt). Infarct areas were smaller in the old male hearts (16.6 ± 1.6%) than in the younger hearts (55.8 ± 1.2%, p < 0.05). By contrast, the hearts from young and old females exhibited a similar post-ischemic functional recovery and no age-dependent difference in infarcts. There was a sex difference in the young group, where ventricular function (LVDP, +dP/dt, −dP/dt) recovered better and infarcts were smaller in females than males. Estradiol levels were highest in young females. Testosterone was high in young males but low in females and old males, which suggested beneficial effects of low testosterone. Indeed, the hearts from GDX males exhibited much better recovery of LVDP in reperfusion than that from intact males (values were 64.4 ± 7.5 % vs. 21.8 ± 9.2%; p < 0.05). The GDX hearts also had smaller infarcts than the hearts from intact males (p < 0.05).ConclusionsAlthough age had no effect on susceptibility to I/R injury after cardioplegic arrest in females, it actually protected against injury in older males. Our findings indicate that low testosterone may be protective against I/R injury following cardioplegic arrest in older males.

Transgenic expression of carbonic anhydrase III in cardiac muscle demonstrates a mechanism to tolerate acidosis.

Carbonic anhydrase III (CAIII) is abundant in liver, adipocytes, and skeletal muscles, but not heart. A cytosolic enzyme that catalyzes conversions between CO2 and in the regulation of intracellular pH, its physiological role in myocytes is not fully understood. Mouse skeletal muscles lacking CAIII showed lower intracellular pH during fatigue, suggesting its function in stress tolerance. We created transgenic mice expressing CAIII in cardiomyocytes that lack endogenous CAIII. The transgenic mice showed normal cardiac development and life span under nonstress conditions. Studies of ex vivo working hearts under normal and acidotic conditions demonstrated that the transgenic and wild-type mouse hearts had similar pumping functions under normal pH. At acidotic pH, however, CAIII transgenic mouse hearts showed significantly less decrease in cardiac function than that of wild-type control as shown by higher ventricular pressure development, systolic and diastolic velocities, and stroke volume via elongating the time of diastolic ejection. In addition to the effect of introducing CAIII into cardiomyocytes on maintaining homeostasis to counter acidotic stress, the results demonstrate the role of carbonic anhydrases in maintaining intracellular pH in muscle cells as a potential mechanism to treat heart failure.

Anti-arrhythmic and cardio-protective effects of atorvastatin and a potent pyridoindole derivative on isolated hearts from rats with metabolic syndrome.

Aims of this study were to investigate the anti-arrhythmic and cardio-protective effect of atorvastatin and of a new pyridoindole derivative (SMe1EC2) on isolated and perfused hearts while following the Langendorff principles. Metabolic syndrome is a widely distributed condition progressing to cardiovascular disease. Many of the metabolic syndrome patients take (HMG)-co-enzyme A (CoA) reductase inhibitors with potential cardio-protective effects. SMe1EC2 is a promising new drug, exerting many positive effects in experimental settings. Rats with induced metabolic syndrome were treated with atorvastatin (25 mg/kg) and SMe1EC2 (25 mg/kg and 0.5 mg/kg, respectively) daily for 3 weeks. After the treatment, the hearts were isolated and perfused according to Langendorff. Both atorvastatin and SMe1EC2 improved cardiac function by elevating the left ventricular developed pressure (VLDP) and cardiac contractility. Both SMe1EC2-treated groups improved LVDP during reperfusion, significantly increased ‒dP/dt, and moderately elevated +dP/dt values. The treatment with both atorvastatin and SMe1EC2 (25 mg/kg) significantly reduced malignant arrhythmia in comparison to control group and group treated with SMe1EC2 0.5 mg/kg. Owing to its anti-arrhythmic and cardio-protective effects, atorvastatin and SMe1EC2 could be of benefit to patients suffering from metabolic syndrome (Tab. 3, Fig. 3, Ref. 41).

Vitamin B complex mitigates cardiac dysfunction in high-methionine diet-induced hyperhomocysteinemia.

This research is designed to test the hypothesis that elevated homocysteine (Hcy) levels in vivo, caused by a deficit in vitamin B complex, promote changes in cardiac function and redox status that lead to heart failure. In order to conduct the study, we used adult male Wistar albino rats (n=30; 4weeks old; 100±15g body weight). Hyperhomocysteinaemia (HHcy) in these animals was achieved by dietary manipulation. For 4weeks, the animals were fed with a standard rodent chow (control, CF), a diet enriched in methionine with no deficiency in B vitamins (i.e., folic acid, B6 and B12) (HMNV) or a diet enriched in methionine and deficient in B vitamins (HMLV). After 28days of dietary manipulation, all animals were killed. The rat hearts were isolated and retrogradely perfused according to the Langendorff technique at a gradually increasing perfusion pressure. We found a negative correlation between elevated serum Hcy and total body and heart weight. The maximum rate of left ventricular pressure development was significantly increased in the HMNV group compared with in the other groups. Systolic left ventricular pressure was significantly changed in all groups. HHcy induces remodelling of the cardiac tissues, as moderate HHcy is associated with more prominent interstitial and perivascular fibrosis. Our results suggest that a high methionine diet without vitamin B complex causes profound negative effects associated with HHcy.

Effect of sevoflurane preconditioning on function of sarcoplasmic reticulum in cardiomyocytes during ischemia-reperfusion in isolated rat hearts

Objective To evaluate the effect of sevoflurane preconditioning on the function of sarcoplasmic reticulum in cardiomyocytes during ischemia-reperfusion (I/R) in isolated rat hearts. Methods Healthy adult male Sprague-Dawley rats, weighing 270-300 g, were anesthetized with intraperitoneal pentobarbital.Their hearts were excised and perfused in a Langendorff apparatus with K-H solution saturated with 95% O2-5% CO2 at 37 ℃.Twenty-four isolated rat hearts successfully perfused in the Langendorff apparatus were divided into 3 groups (n=8 each) using a random number table: control group (group C), I/R group and sevoflurane preconditioning group (group SP). Myocardial ischemia was induced by interrupting perfusion for 30 min followed by 120 min reperfusion.In group SP, the hearts were perfused with 2.4% sevoflurane for 10 min starting from 10 min before ischemia.Left ventricular developed pressure (LVDP) and left ventricular end-diastolic pressure (LVEDP) were recorded at 5, 10, 15, 30 and 60 min of reperfusion.Coronary effluent was collected at 10 min before reperfusion for measurement of the levels of lactate dehydrogenase (LDH) and cardiac troponin I (cTnI). Myocardial specimens were obtained at 120 min of reperfusion for examination of the pathological changes (using HE staining) and for determination of myocardial infarct size (by TTC staining), sarcoendoplasmic reticulum Ca2+ -ATPase (SERCA2a) activity (with a spectrophotometer) and expression of Bcl-2, Bax and SERCA2a (by Western blot). Results Compared with group C, LVDP was significantly decreased and LVEDP was increased at each time point, myocardial infarct size was increased, the levels of LDH and cTnI in coronary effluent were increased, the expression of Bax was up-regulated, the expression of Bcl-2 and SERCA2a was down-regulated, and the activity of SERCA2a was decreased in group I/R (P<0.01). Compared with group I/R, LVDP was significantly increased and LVEDP was decreased at each time point, myocardial infarct size was decreased, the levels of LDH and cTnI in coronary effluent were decreased, the expression of Bax was down-regulated, the expression of Bcl-2 and SERCA2a was up-regulated, the activity of SERCA2a was increased (P<0.01), and the pathological changes were significantly attenuated in group SP. Conclusion The mechanism by which sevoflurane preconditioning reduces I/R injury in isolated rat hearts may be related to improving the function of sarcoplasmic reticulum in cardiomyocytes. Key words: Anesthetics, inhalation; Ischemic preconditioning; Myocardial reperfusion injury; Sarcoplasmic reticulum

A protocol to study ex vivo mouse working heart at human-like heart rate

Genetically modified mice are widely used as experimental models to study human heart function and diseases. However, the fast rate of normal mouse heart at 400–600bpm limits its capacity of assessing kinetic parameters that are important for the physiology and pathophysiology of human heart that beats at a much slower rate (75–180bpm). To extend the value of mouse models, we established a protocol to study ex vivo mouse working hearts at a human-like heart rate. In the presence of 300μM lidocaine to lower pacemaker and conductive activities and prevent arrhythmia, a stable rate of 120–130bpm at 37°C is achieved for ex vivo mouse working hearts. The negative effects of decreased heart rate on force-frequency dependence and lidocaine as a myocardial depressant on intracellular calcium can be compensated by using a higher but still physiological level of calcium (2.75mM) in the perfusion media. Multiple parameters were studied to compare the function at the human-like heart rate with that of ex vivo mouse working hearts at the standard rate of 480bpm. The results showed that the conditions for slower heart rate in the presence of 300μM lidocaine did not have depressing effect on left ventricular pressure development, systolic and diastolic velocities and stroke volume with maintained positive inotropic and lusitropic responses to β-adrenergic stimulation. Compared with that at 480bpm, the human-like heart rate increased ventricular filling and end diastolic volume with enhanced Frank-Starling responses. Coronary perfusion was increased from longer relaxation time and interval between beats whereas cardiac efficiency was significantly improved. Although the intrinsic differences between mouse and human heart remain, this methodology for ex vivo mouse hearts to work at human-like heart rate extends the value of using genetically modified mouse models to study cardiac function and human heart diseases.

Endothelial Nitric Oxide Synthase-Induced Hypertrophy and Vascular Dysfunction Contribute to the Left Ventricular Dysfunction in Caveolin-1−/− Mice

BackgroundCaveolin-1 (Cav1)−/− mice display impaired development of left ventricular pressure and increased left ventricular wall thickness but no dilated ventricle; these are typical findings in patients with heart failure with preserved ejection fraction (HfpEF). Aiming to clarify if dysfunctional endothelial nitric oxide synthase (eNOS) influences cardiomyocyte contractility, cardiac conduction system, or afterload/vascular resistance, we studied Cav1−/−/eNOS−/− mice. MethodsCardiac function was assessed in vivo by pressure-volume-catheterization of the left ventricle, echocardiography and electrocardiography. In addition, isolated tissue experiments were performed to evaluate cardiomyocyte contractility (atria) and vessel morphology and function (aorta). Histology, immunoblotting and quantitative polymerase chain reaction were applied to characterise radical formation and oxidative stress in the heart. ResultsCardiac hypertrophy was completely reversed in Cav1−/−/eNOS−/− mice. The impaired pump function in Cav1−/− mice was significantly improved in Cav1−/−/eNOS−/− mice, but no complete alignment with eNOS−/− controls was achieved, indicating an additional eNOS-independent mechanism contributing to HFpEF in Cav1−/− mice. It is unlikely that frequently occurring arrhythmias contributed to HFpEF in Cav1−/− mice. In contrast, numerous eNOS-dependent and eNOS-independent vascular abnomalities could explain the cardiac phenotypes of Cav1−/− mice. ConclusionsSynergistic effects between eNOS-related cardiac hypertrophy and vascular hypercontractility appear to underlie the left ventricular dysfunction in Cav1−/−mice. These findings provide insights relevant to the poorly understood pathophysiology of HFpEF.

The autonomic nervous system and cardiac GLP-1 receptors control heart rate in mice

ObjectivesGlucagon-like peptide-1 (GLP-1) is secreted from enteroendocrine cells and exerts a broad number of metabolic actions through activation of a single GLP-1 receptor (GLP-1R). The cardiovascular actions of GLP-1 have garnered increasing attention as GLP-1R agonists are used to treat human subjects with diabetes and obesity that may be at increased risk for development of heart disease. Here we studied mechanisms linking GLP-1R activation to control of heart rate (HR) in mice. MethodsThe actions of GLP-1R agonists were examined on the control of HR in wild type mice (WT) and in mice with cardiomyocyte-selective disruption of the GLP-1R (Glp1rCM−/−). Complimentary studies examined the effects of GLP-1R agonists in mice co-administered propranolol or atropine. The direct effects of GLP-1R agonism on HR and ventricular developed pressure were examined in isolated perfused mouse hearts ex vivo, and atrial depolarization was quantified in mouse hearts following direct application of liraglutide to perfused atrial preparations ex vivo. ResultsDoses of liraglutide and lixisenatide that were equipotent for acute glucose control rapidly increased HR in WT and Glp1rCM−/− mice in vivo. The actions of liraglutide to increase HR were more sustained relative to lixisenatide, and diminished in Glp1rCM−/− mice. The acute chronotropic actions of GLP-1R agonists were attenuated by propranolol but not atropine. Neither native GLP-1 nor lixisenatide increased HR or developed pressure in perfused hearts ex vivo. Moreover, liraglutide had no direct effect on sinoatrial node firing rate in mouse atrial preparations ex vivo. Despite co-localization of HCN4 and GLP-1R in primate hearts, HCN4-directed Cre expression did not attenuate levels of Glp1r mRNA transcripts, but did reduce atrial Gcgr expression in the mouse heart. ConclusionsGLP-1R agonists increase HR through multiple mechanisms, including regulation of autonomic nervous system function, and activation of the atrial GLP-1R. Surprisingly, the isolated atrial GLP-1R does not transduce a direct chronotropic effect following exposure to GLP-1R agonists in the intact heart, or isolated atrium, ex vivo. Hence, cardiac GLP-1R circuits controlling HR require neural inputs and do not function in a heart-autonomous manner.