Heart protection by combination therapy with esmolol and milrinone at late-ischemia and early reperfusion

Esmolol upregulates the α7 nAChR/STAT3/NF-κB pathway by decreasing the ubiquitin and increasing the ChAT+CD4+ T lymphocyte to alleviate inflammation in septic cardiomyopathy

Esmolol has been demonstrated to mitigate inflammation damage and T lymphocyte apoptosis in septic cardiomyopathy. It has been established that the activation of α7 nicotinic acetylcholine receptor (nAChR) by cluster of differentiation 4(CD4) + T lymphocytes expressing choline acetyltransferase (ChAT) can prevent excessive inflammation and reduce splenocyte apoptosis in septic cardiomyopathy. Given the similar anti-inflammatory effects, we hypothesized that esmolol might be associated with α7 nAChR and thereby exert its cardioprotective functions. In the cecal ligation puncture (CLP)-induced rat septic cardiomyopathy model, esmolol was found to attenuate myocardial injury as evidenced by Hematoxylin and Eosin (HE) staining, terminal deoxynucleotidyl transferase dUTP nick end labelling (TUNEL) assay, and the reduced concentration of interleukin (IL)-1, IL-6, and Tumor Necrosis Factor (TNF)-α detected by enzyme-linked immunosorbent assay (ELISA). Western blotting (WB) revealed that esmolol enhanced the expression of α7 nAChR, elevated the level of Phosphorylated-Signal transducer and activator of transcription 3 (P-STAT3)/STAT3, and decreased the level of Nuclear factor-κB (NF-κB), which led to the reduction of plasma IL-1, IL-6, and TNF-α. Methyl lycaconitine Citrate (MLA, an α7 nAChR inhibitor) suppressed the level of P-STAT3/STAT3, while stattic (a STAT3 inhibitor) inhibited the level of P-STAT3/STAT3 and up-regulated the expression of NF-κB. Real-time quantitative PCR (RT-qPCR) results indicated no significant difference in the mRNA level of α7 nAChR, but immunofluorescence and WB results verified the upregulation of α7 nAChR by esmolol and the reduction of ubiquitin induced by esmolol. In the spleen, esmolol decreased splenocyte apoptosis and increased the expression of α7 nAChR as shown by immunofluorescence. In isolated CD4+ T cells obtained through magnetic cell separation, esmolol enhanced the expression of ChAT mRNA. In conclusion, esmolol upregulates α7 nAChR by decreasing ubiquitin and increasing ChAT+CD4+ T lymphocytes and then increases the P-STAT3/STAT3 which inhibits NF-κB thus alleviating inflammation in septic cardiomyopathy.

Peroxisome proliferator-activated receptor gamma ( PPARG )-mediated myocardial salvage in acute myocardial infarction managed with left ventricular unloading and coronary reperfusion

Ischemic heart disease and acute myocardial infarction (AMI) is a leading cause of morbidity and mortality. Improvements have been made in coronary interventions to restore blood flow, but ischemia/reperfusion (I/R) injury significantly impacts clinical outcomes. We previously reported that activation of percutaneous mechanical unloading of the left ventricle (LV) with a transvalvular axial-flow device simultaneously with reperfusion improves myocardial salvage. However, the underlying mechanisms, potential adjuvant pharmacological interventions and the timing of the use of LV unloading as a cardioprotective approach in AMI are not well understood. This study investigated a) the mechanisms associated with improved myocardial salvage, b) a pharmacological intervention, and c) the timing of LV unloading. Following 90 minutes of ischemia, adult swine were subjected to reperfusion alone, simultaneous unloading with reperfusion, upfront unloading with delayed reperfusion, upfront reperfusion with delayed unloading, or reperfusion with concurrent use of esmolol and milrinone. Compared to controls, the simultaneous group had a 47% increase in myocardial salvage following AMI. This was associated with increased expression of neutrophil degranulation, macrophage activation, iNOS signaling, wound healing, and PPAR signaling. From these pathways, PPARG (peroxisome proliferator-activated receptor gamma) emerged as a potential cardioprotective gene that was uniquely overexpressed in the simultaneously unloaded and reperfused myocardium. Next, we showed PPARG agonism with rosiglitazone reduces mitochondrial oxygen demand in cardiomyocytes and in vivo, improves myocardial salvage following I/R injury in C57BL6/J mice. Thiazolidinediones (TZDs), such as rosiglitazone could be investigated as therapies combined with simultaneous LV unloading and coronary interventions to mitigate reperfusion injury.

GRAPHICAL ABSTRACT

A model-agnostic framework to enhance knowledge graph-based drug combination prediction with drug-drug interaction data and supervised contrastive learning

Combination therapies have brought significant advancements to the treatment of various diseases in the medical field. However, searching for effective drug combinations remains a major challenge due to the vast number of possible combinations. Biomedical knowledge graph (KG)-based methods have shown potential in predicting effective combinations for wide spectrum of diseases, but the lack of credible negative samples has limited the prediction performance of machine learning models. To address this issue, we propose a novel model-agnostic framework that leverages existing drug-drug interaction (DDI) data as a reliable negative dataset and employs supervised contrastive learning (SCL) to transform drug embedding vectors to be more suitable for drug combination prediction. We conducted extensive experiments using various network embedding algorithms, including random walk and graph neural networks, on a biomedical KG. Our framework significantly improved performance metrics compared to the baseline framework. We also provide embedding space visualizations and case studies that demonstrate the effectiveness of our approach. This work highlights the potential of using DDI data and SCL in finding tighter decision boundaries for predicting effective drug combinations.

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.

Albumin Nanoparticle Formulation for Heart-Targeted Drug Delivery: In Vivo Assessment of Congestive Heart Failure

Congestive heart failure is a fatal cardiovascular disease resulting in tissue necrosis and loss of cardiac contractile function. Inotropic drugs such as milrinone are commonly used to improve the myocardial contractility and heart function. However, milrinone is associated with severe side effects and lower circulation time. In this article, a novel protein nanoparticle formulation for heart-targeted delivery of milrinone has been designed and tested. The formulation was prepared using albumin protein conjugated with the targeting ligand, angiotensin II peptide to form nanoparticles following the ethanol desolvation method. The formulation was characterized for size, charge, and morphology and tested in a rat model of congestive heart failure to study pharmacokinetics, biodistribution, and efficacy. The overall cardiac output parameters were evaluated comparing the formulation with the control non-targeted drug, milrinone lactate. This formulation exhibited improved pharmacokinetics with a mean retention time of 123.7 min, half-life of 101.3 min, and clearance rate of 0.24 L/(kg*h). The targeted formulation also significantly improved ejection fraction and fractional shortening parameters thus improving cardiac function. This study demonstrates a new approach in delivering inotropic drugs such as milrinone for superior treatment of congestive heart failure.

Combination of the Phosphodiesterase Inhibitors Sildenafil and Milrinone Induces Cardioprotection With Various Conditioning Strategies

Ischemic preconditioning and postconditioning are strong measures preserving the heart against ischemia-reperfusion injury in experimental setting but are too invasive and impractical for clinical routine. The cardioprotective effects of ischemic preconditioning and postconditioning can be imitated pharmacologically, for example, with the phosphodiesterase inhibitors sildenafil and milrinone. We hypothesize that sildenafil-induced preconditioning is concentration dependent and further that a combined treatment of "nonprotective" versus "protective" concentrations of sildenafil and milrinone leads to a significant infarct size reduction. Experiments were performed on isolated hearts of male Wistar rats, randomized into 12 groups, mounted onto a Langendorff system, and perfused with Krebs-Henseleit buffer. All hearts underwent 33 minutes ischemia and 60 minutes of reperfusion. For determination of a concentration-dependent effect of sildenafil, hearts were perfused with increasing concentrations of sildenafil (0.1-1 µM) over 10 minutes before ischemia. In a second series of experiments, hearts were treated with 0.3 µM sildenafil or 1 µM milrinone as the "protective" concentrations. A higher concentration of respective drugs did not further reduce infarct size. In addition, a combination of "protective" and "nonprotective" concentrations of sildenafil and milrinone was applied. Sildenafil and milrinone in lower concentrations led to significant infarct size reduction, whereas combining both substances in cardioprotective concentrations did not enhance this effect. Sildenafil in a concentration of 0.3 µM induces myocardial protection. Furthermore, treatment with sildenafil and milrinone in lower concentrations had an equally strong cardioprotective effect regarding infarct size reduction compared with the administration of "protective" concentrations.

Polymer Conjugation of Docosahexaenoic Acid Potentiates Cardioprotective Therapy in Preclinical Models of Myocardial Ischemia/Reperfusion Injury

While coronary angioplasty represents an effective treatment option following acute myocardial infarction, the reperfusion of the occluded coronary artery can prompt ischemia-reperfusion (I/R) injury that significantly impacts patient outcomes. As ω-3 polyunsaturated fatty acids (PUFAs) have proven, yet limited cardioprotective abilities, an optimized polymer-conjugation approach is reported that improves PUFAs bioavailability to enhance cardioprotection and recovery in animal models of I/R-induced injury. Poly-l-glutamic acid (PGA) conjugation improves the solubility and stability of di-docosahexaenoic acid (diDHA) under physiological conditions and protects rat neonatal ventricular myocytes from I/R injury by reducing apoptosis, attenuating autophagy, inhibiting reactive oxygen species generation, and restoring mitochondrial membrane potential. Enhanced protective abilities are associated with optimized diDHA loading and evidence is provided for the inherent cardioprotective potential of PGA itself. Pretreatment with PGA-diDHA before reperfusion in a small animal I/R model provides for cardioprotection and limits area at risk (AAR). Furthermore, the preliminary findings suggest that PGA-diDHA administration in a swine I/R model may provide cardioprotection, limit edema and decrease AAR. Overall, the evaluation of PGA-diDHA in relevant preclinical models provides evidence for the potential of polymer-conjugated PUFAs in the mitigation of I/R injury associated with coronary angioplasty.

Pharmacological postconditioning: a molecular aspect in ischemic injury

OBJECTIVE

Ischaemia/reperfusion (I/R) injury is defined as the damage to the tissue which is caused when blood supply returns to tissue after ischaemia. To protect the ischaemic tissue from irreversible injury, various protective agents have been studied but the benefits have not been clinically applicable due to monotargeting, low potency, late delivery or poor tolerability.

KEY FINDINGS

Strategies involving preconditioning or postconditioning can address the issues related to the failure of protective therapies. In principle, postconditioning (PoCo) is clinically more applicable in the conditions in which there is unannounced ischaemic event. Moreover, PoCo is an attractive beneficial strategy as it can be induced rapidly at the onset of reperfusion via series of brief I/R cycles following a major ischaemic event or it can be induced in a delayed manner. Various pharmacological postconditioning (pPoCo) mechanisms have been investigated systematically. Using different animal models, most of the studies on pPoCo have been carried out preclinically.

SUMMARY

However, there is a need for the optimization of the clinical protocols to quicken pPoCo clinical translation for future studies. This review summarizes the involvement of various receptors and signalling pathways in the protective mechanisms of pPoCo.

Milrinone-Induced Pharmacological Preconditioning in Cardioprotection: Hints for a Role of Mitochondrial Mechanisms

The activation of mitochondrial calcium-sensitive potassium (mBK_Ca) channels is crucially involved in cardioprotection induced by preconditioning. For milrinone (Mil)-induced preconditioning, the involvement of mBK_Ca-channels and further mitochondrial signaling is unknown. We hypothesize that (1) Mil-induced preconditioning is concentration-dependent and (2) that the activation of mBK_Ca-channels, release of reactive oxygen species (ROS), and the mitochondrial permeability transition pore (mPTP) could be involved. Isolated hearts of male Wistar rats were perfused with Krebs-Henseleit buffer and underwent 33 min of ischemia followed by 60 min of reperfusion. For determination of a concentration-dependent effect of Mil, hearts were perfused with different concentrations of Mil (0.3–10 µM) over 10 min before ischemia. In a second set of experiments, in addition to controls, hearts were pretreated with the lowest protective concentration of 1 µM Mil either alone or combined with the mBK_Ca-channel blocker paxilline (Pax + Mil), or paxilline alone (Pax). In additional groups, Mil was administered with and without the ROS scavenger N-2-mercaptopropionylglycine (MPG + Mil, MPG) or the mPTP inhibitor cyclosporine A (MPG + Mil + CsA, CsA + Mil), respectively. Infarct sizes were determined by triphenyltetrazolium chloride (TTC) staining. The lowest and most cardioprotective concentration was 1 µM Mil (Mil 1: 32 ± 6%; p < 0.05 vs. Con: 63 ± 8% and Mil 0.3: 49 ± 6%). Pax and MPG blocked the infarct size reduction of Mil (Pax + Mil: 53 ± 6%, MPG + Mil: 59 ± 7%; p < 0.05 vs. Mil: 34 ± 6%) without having an effect on infarct size when administered alone (Pax: 53 ± 7%, MPG: 58 ± 5%; ns vs. Con). The combined administration of CsA completely restored the MPG-inhibited cardioprotection of Mil (MPG + Mil + CsA: 35 ± 7%, p < 0.05 vs. MPG + Mil). Milrinone concentration-dependently induces preconditioning. Cardioprotection is mediated by the activation of mBK_Ca-channels, release of ROS and mPTP inhibition.

Multitarget Strategies to Reduce Myocardial Ischemia/Reperfusion Injury: JACC Review Topic of the Week

Many treatments have been identified that confer robust cardioprotection in experimental animal models of acute ischemia and reperfusion injury. However, translation of these cardioprotective therapies into the clinical setting of acute myocardial infarction (AMI) for patient benefit has been disappointing. One important reason might be that AMI is multifactorial, causing cardiomyocyte death via multiple mechanisms, as well as affecting other cell types, including platelets, fibroblasts, endothelial and smooth muscle cells, and immune cells. Many cardioprotective strategies act through common end-effectors and may be suboptimal in patients with comorbidities. In this regard, emerging data suggest that optimal cardioprotection may require the combination of additive or synergistic multitarget therapies. This review will present an overview of the state of cardioprotection today and provide a roadmap for how we might progress towards successful clinical use of cardioprotective therapies following AMI, focusing on the rational combination of judiciously selected, multitarget therapies. This paper emerged as part of the discussions of the European Union (EU)-CARDIOPROTECTION Cooperation in Science and Technology (COST) Action, CA16225.

Stimulation of the Beta2 Adrenergic Receptor at Reperfusion Limits Myocardial Reperfusion Injury via an Interleukin-10-Dependent Anti-Inflammatory Pathway in the Spleen

BACKGROUND

In addition to the airway-relaxing effects, β2 adrenergic receptor (β2AR) agonists are also found to have broad anti-inflammatory effects. The current study was conducted to define the role of β2AR agonists in limiting myocardial ischemia/reperfusion injury (IRI).

METHODS AND RESULTS

Adult male wild-type (WT) and interleukin (IL)-10 knockout (KO) mice underwent a 40-min left coronary artery ligation and 60-min reperfusion. A selective β2AR agonist, Clenbuterol, at doses of 0.1 μg or 1 μg/g weight i.v. 5 min before reperfusion, significantly reduced myocardial infarct size (IS) by 28% and 39% (vs. control, P<0.05) in WT mice respectively, but had no protective effect in IL-10 KO mice. Inhalational therapy with nebulized Clenbuterol, Albuterol, Salmeterol or Arformoterol immediately before ischemia significantly reduced IS (P<0.05) in WT mice. Splenectomy similarly reduced IS as Clenbuterol-treated mice, but intravenous Clenbuterol did not further reduce IS in splenectomized mice. In splenectomized WT mice, acute transfer of isolated splenocytes, not the Clenbuterol-pretreated splenocytes, restored the myocardial IS to the level of intact mice. Intravenous Clenbuterol significantly increased splenic protein levels of β2AR, phosphorylated Akt and IL-10 and plasma IL-10, and inhibited the expression of pro-inflammatory mRNAs.

CONCLUSIONS

Both intravenous and inhalational β2AR agonists exert a cardioprotective effect against IRI by activating the anti-inflammatory β2AR-IL-10 pathway.

Milrinone-Induced Postconditioning Requires Activation of Mitochondrial Ca2+-sensitive Potassium (mBKCa) Channels

OBJECTIVES

Cardioprotection by postconditioning requires activation of mitochondrial large-conductance Ca2+-sensitive potassium (mBKCa) channels. The involvement of these channels in milrinone-induced postconditioning is unknown. The authors determined whether cardioprotection by milrinone-induced postconditioning involves activation of mBKCa channels in the rat heart in vitro.

DESIGN

Randomized, prospective, blinded laboratory investigation.

SETTING

Experimental laboratory.

PARTICIPANTS

Male Wistar rats.

INTERVENTIONS

Hearts of male Wistar rats were randomized, placed on a Langendorff system, and perfused with Krebs-Henseleit buffer at a constant pressure of 80 mmHg. All hearts were subjected to 33 minutes of global ischemia and 60 minutes of reperfusion. At the onset of reperfusion, hearts were perfused with different concentrations of milrinone (0.3-100 μM) for determination of a dose-effect curve. In a second set of experiments, 3 μM milrinone was administered in combination with the mBKCa channel inhibitor paxilline (1 μM). Infarct size was determined by triphenyltetrazoliumchloride staining.

MEASUREMENTS AND MAIN RESULTS

In control animals, infarct size was 37 ± 7%. Milrinone at a concentration of 3 μM reduced infarct size to 22 ± 7% (p < 0.05 v control). Higher milrinone concentrations did not confer stronger protection. Paxilline completely blocked milrinone-induced cardioprotection whereas paxilline alone had no effect on infarct size.

CONCLUSIONS

This study shows that activation of mBKCa channels plays a pivotal role in milrinone-induced postconditioning.

Reduction of chlorpyrifos-induced toxicity in human lymphocytes by selected phosphodiesterase inhibitors

One of the most famous and commonly used compounds from organophosphate (OP) family is chlorpyrifos (CP) which is widespreadly used as a powerful insecticide. Previous studies have shown that OPs induce oxidative stress, inflammation and apoptosis by generating the free radicals. The protective effects of three members of phosphodiesterase inhibitor (PDEI) family, including rolipram (RLP), milrinon (MLR) and pentoxifylline (PTX) were evaluated in the human lymphocytes against CP's toxicity. In this case, the level of oxidative stress biomarkers, the viability of the cells and the rate of apoptosis by flow cytometry were investigated. The results of this study revealed that CP makes a significant increase in the level of inflammatory and oxidative stress markers such as meyloperoxidase (MPO), lipid peroxidation (LPO), total thiol molecules (TTM) and total antioxidant potential (TAP), and also makes an enhancement in the rate of apoptosis process. On the other hand, PDEIs and specifically the combination of them restored the negative effects of CP and significantly prevented the apoptosis and oxidative stress imbalance. It is concluded that these PDEIs have positive effects in attenuation, recovery, and protection of CP-induced toxicity in the human lymphocytes.

An electrocardiographic, molecular and biochemical approach to explore the cardioprotective effect of vasopressin and milrinone against phosphide toxicity in rats

The present study was conducted to identify the protective effect of vasopressin (AVP) and milrinone on cardiovascular function, mitochondrial complex activities, cellular ATP reserve, oxidative stress, and apoptosis in rats poisoned by aluminum phosphide (AlP). Rats were divided into five groups (n = 12) including control, AlP (12.5 mg/kg), AlP + AVP (2.0 Units/kg), AlP + milrinone (0.25 mg/kg) and AlP + AVP + milrinone. After treatment, the animals were connected to an electronic cardiovascular monitoring device to monitor electrocardiographic (ECG) parameter. Finally, oxidative stress biomarkers, mitochondrial complex activities, ADP/ATP ratio and apoptosis were evaluated on the heart tissues. Results indicated that AlP administration induced ECG abnormalities along with a decline in blood pressure and heart rate. AVP and milrinone significantly ameliorated these changes in all treated groups. Considerable protective effects on oxidative stress biomarkers, complex IV activity, ADP/ATP ratio and caspase-3 and -9 activities in treated groups were also found. These findings were supported by flow cytometry assay of cardiomyocytes. In conclusion, administration of AVP and milrinone, not only improve cardiovascular functions in AlP poisoned rats in the short time, but after a long time can also restore mitochondrial function and ATP level and reduce the oxidative damage, which prevent cardiomyocytes from entering the apoptotic phase.

Sustained release of milrinone delivered via microparticles in a rodent model of myocardial infarction

OBJECTIVE

The aim of the present study was to construct a new drug delivery system for milrinone using microparticles. This novel technology enhances drug bioavailability and decreases toxicity, with future implications for the treatment of end-stage heart failure.

METHODS

Polylactic-co-glycolic acid microparticles (PLGA-MPs) loaded with milrinone were prepared using a double emulsion-solvent evaporation technique. In vitro release kinetics was evaluated at physiologic conditions. A total of 24 female Lewis rats underwent left coronary artery ligation. One week after ligation, all rats were randomized to 1 of 3 groups (n=8 per group). Group I received an intravenous injection of PLGA-MPs alone; group II, a bolus intravenous injection of milrinone; and group III an intravenous injection of milrinone-PLGA-MPs. All injections were administrated slowly by way of the tail vein over 10 minutes. Transthoracic echocardiography, noninvasive heart rate monitoring, and blood pressure measurements were performed at different predetermined intervals before and for 24 hours after the injection. All rats survived for 24 hours and were then killed by euthanasia. Serum plasma was taken for cytokine assays and determination of milrinone levels using high-performance liquid chromatography.

RESULTS

Group III had a significantly greater left ventricular ejection fraction at 90 minutes and 3, 6, and 12 hours after treatment compared with the other groups. The milrinone plasma level was significantly greater in group III than in the other groups (group I, 0 ng/mL; group II, 1.7±2.4 ng/mL; group III, 9.1±2.2 ng/mL; P<.05). The intercellular adhesion molecule and cytokine-induced neutrophil chemoattractant-1 levels were significantly lower in group III than in the other 2 groups (P<.05).

CONCLUSIONS

Drug encapsulation using microparticles can prolong the effects of milrinone. We propose a new strategy for future drug delivery in patients with end-stage heart failure.

Safety of combination therapy with milrinone and esmolol for heart protection during percutaneous coronary intervention in acute myocardial infarction

PURPOSE

Ischemia/reperfusion injury remains an untreated clinical problem in patients with acute myocardial infarction (AMI) despite significant advances in emergent revascularization through percutaneous coronary intervention (PCI). Pharmacological intervention for infarct size reduction is unavailable. We have identified that the medications milrinone and esmolol, when administered together at the beginning of the reperfusion, significantly decrease infarct size via reducing reperfusion injury in an experimental model. The present study tested the safety of combination therapy of milrinone and esmolol (M + E) in patients with AMI.

METHODS

Sixteen subjects with AMI requiring PCI were consecutively recruited. M + E was intravenously infused simultaneously for 10 min started at 5 min before anticipated angioplasty balloon inflation. Another 16 consecutively recruited AMI patients requiring PCI served as a placebo arm treated per routine clinical protocol. Blood pressure (BP) and heart rate (HR) were monitored continuously during PCI.

RESULTS

M + E combination therapy resulted in a trend of non-significant reduction in BP compared with a control group. There was a modest but significant increase in HR at the later phase of M + E infusion compared with a control group. No significant cardiac arrhythmia was induced during M + E infusion.

CONCLUSIONS

The combination therapy with M + E produces a minimal change in hemodynamics and appears safe as an adjunctive therapy to PCI in AMI patients. Further studies are warranted.

Milrinone and levosimendan during porcine myocardial ischemia -- no effects on calcium overload and metabolism

BACKGROUND

Although inotropic stimulation is considered harmful in the presence of myocardial ischaemia, both calcium sensitisers and phosphodiesterase inhibitors may offer cardioprotection. We hypothesise that these cardioprotective effects are related to an acute alteration of myocardial metabolism. We studied in vivo effects of milrinone and levosimendan on calcium overload and ischaemic markers using left ventricular microdialysis in pigs with acute myocardial ischaemia.

METHODS

Anaesthetised juvenile pigs, average weight 36 kg, were randomised to one of three intravenous treatment groups: milrinone 50 μg/kg bolus plus infusion 0.5 μg/kg/min (n = 7), levosimendan 24 μg/kg plus infusion 0.2 μg/kg/min (n = 7), or placebo (n = 6) for 60 min prior to and during a 45 min acute regional coronary occlusion. Systemic and myocardial haemodynamics were assessed, and microdialysis was performed with catheters positioned in the left ventricular wall. (45) Ca(2+) was included in the microperfusate in order to assess local calcium uptake into myocardial cells. The microdialysate was analysed for glucose, lactate, pyruvate, glycerol, and for (45) Ca(2+) recovery.

RESULTS

During ischaemia, there were no differences in microdialysate-measured parameters between control animals and milrinone- or levosimendan-treated groups. In the pre-ischaemic period, arterial blood pressure decreased in all groups while myocardial oxygen consumption remained stable.

CONCLUSIONS

These findings reject the hypothesis of an immediate energy-conserving effect of milrinone and levosimendan during acute myocardial ischaemia. On the other hand, the data show that inotropic support with milrinone and levosimendan does not worsen the metabolic parameters that were measured in the ischaemic myocardium.

Hyperglycemia raises the threshold of levosimendan- but not milrinone-induced postconditioning in rat hearts

Background

The authors examined whether milrinone and levosimendan could exert cardiac postconditioning effects in rats under normoglycemia and hyperglycemia, and whether the effects could be mediated by mitochondrial permeability transition pore (mPTP).

Methods

Wistar rats underwent 30-min coronary artery occlusion followed by 2-h reperfusion. The rats received milrinone or levosimendan just before reperfusion under normoglycemic or hyperglycemic conditions with or without atractyloside, an mPTP opener.

Results

Under normoglycemia, both 30 μg/kg milrinone (29 ± 12%) and 10 μg/kg levosimendan (33 ± 13%) reduced infarct size compared with that in the control (58 ± 7%). Under hyperglycemia, milrinone (34 ± 13%) reduced infarct size at the same dose as under normoglycemia. In contrast, neither 10 nor 30 μg/kg levosimendan protected hyperglycemic hearts, and only 100 μg/kg levosimendan (32 ± 9%) reduced infarct size compared with that in the hyperglycemic control (58 ± 13%). All of these cardioprotective effects under normoglycemia and hyperglycemia are abolished by atractyloside.

Conclusion

Milrinone and levosimendan exert postconditioning effects via inhibition of mPTP opening. Hyperglycemia raises the threshold of levosimendan-induced postconditioning, while milrinone-induced postconditioning is not influenced by hyperglycemia.