Transcardiac serotonin concentration is increased in selected patients with limiting angina and complex coronary lesion morphology

Role of Vasoactive Hormone-Induced Signal Transduction in Cardiac Hypertrophy and Heart Failure

Heart failure is the common concluding pathway for a majority of cardiovascular diseases and is associated with cardiac dysfunction. Since heart failure is invariably preceded by adaptive or maladaptive cardiac hypertrophy, several biochemical mechanisms have been proposed to explain the development of cardiac hypertrophy and progression to heart failure. One of these includes the activation of different neuroendocrine systems for elevating the circulating levels of different vasoactive hormones such as catecholamines, angiotensin II, vasopressin, serotonin and endothelins. All these hormones are released in the circulation and stimulate different signal transduction systems by acting on their respective receptors on the cell membrane to promote protein synthesis in cardiomyocytes and induce cardiac hypertrophy. The elevated levels of these vasoactive hormones induce hemodynamic overload, increase ventricular wall tension, increase protein synthesis and the occurrence of cardiac remodeling. In addition, there occurs an increase in proinflammatory cytokines and collagen synthesis for the induction of myocardial fibrosis and the transition of adaptive to maladaptive hypertrophy. The prolonged exposure of the hypertrophied heart to these vasoactive hormones has been reported to result in the oxidation of catecholamines and serotonin via monoamine oxidase as well as the activation of NADPH oxidase via angiotensin II and endothelins to promote oxidative stress. The development of oxidative stress produces subcellular defects, Ca2+-handling abnormalities, mitochondrial Ca2+-overload and cardiac dysfunction by activating different proteases and depressing cardiac gene expression, in addition to destabilizing the extracellular matrix upon activating some metalloproteinases. These observations support the view that elevated levels of various vasoactive hormones, by producing hemodynamic overload and activating their respective receptor-mediated signal transduction mechanisms, induce cardiac hypertrophy. Furthermore, the occurrence of oxidative stress due to the prolonged exposure of the hypertrophied heart to these hormones plays a critical role in the progression of heart failure.

Comparative Effectiveness and Safety of Ticagrelor Versus Clopidogrel for Elderly Chinese Patients Undergoing Percutaneous Coronary Intervention: A Single-Center Retrospective Cohort Study

BACKGROUND

Taking ischemic and bleeding risks into consideration, insufficient data exist on dual antiplatelet therapy after percutaneous coronary intervention in elderly Chinese patients with coronary artery disease.

OBJECTIVE

We aimed to investigate the effectiveness and safety of ticagrelor in comparison with clopidogrel on a background of aspirin for elderly Chinese patients with coronary artery disease 12 months after percutaneous coronary intervention.

METHODS

A single-center retrospective cohort study was conducted. Selected from patients with coronary artery disease aged ≥ 75 years from January 2010 to July 2019, 908 eligible subjects receiving dual antiplatelet therapy after percutaneous coronary intervention for up to 12 months were consecutively enrolled in the study. The included patients received ticagrelor in combination with aspirin (n = 264) or clopidogrel in combination with aspirin (n = 644). Effectiveness endpoints were evaluated by the major adverse cardiovascular events, encompassing all-cause death, non-fatal myocardial infarction, and clinically driven revascularization. The safety endpoints were recorded as the incidence of Bleeding Academic Research Consortium bleeding.

RESULTS

The patients who were treated with ticagrelor were slightly younger than those who were treated with clopidogrel (79.1 ± 3.7 vs 80.7 ± 4.5 years, p < 0.01). The ticagrelor cohort contained a higher percentage of patients undergoing a prior percutaneous coronary intervention (37.9% vs 24.5%, p < 0.01), and a lower percentage of smokers (19.3% vs 27.2%, p < 0.05), compared with the clopidogrel cohort. The levels of glucose, total cholesterol, and low-density lipoprotein-cholesterol in the ticagrelor group were higher while the level of triglycerides and high-density lipoprotein-cholesterol were lower (p < 0.05) than those in the clopidogrel group. Left main percutaneous coronary intervention was performed more frequently among the ticagrelor-treated patients (23.5% vs 9.3%, p < 0.01), while patients in the clopidogrel group underwent more left circumflex percutaneous coronary intervention (34.3% vs 23.1%, p < 0.01). We found that ticagrelor was associated with a lower incidence of major adverse cardiovascular events than clopidogrel using the inverse probability of treatment weighting model (odds ratio, 0.493; 95% confidence interval 0.356-0.684). There was no difference in terms of the risk of Bleeding Academic Research Consortium bleeding between the two groups (p > 0.05).

CONCLUSIONS

Ticagrelor was associated with a lower incidence of major adverse cardiovascular events than clopidogrel at 12 months in elderly Chinese patients with coronary artery disease, without a significant increase of Bleeding Academic Research Consortium bleeding events.

Effects of Cyproheptadine on Mitral Valve Remodeling and Regurgitation After Myocardial Infarction

BACKGROUND

Ischemic mitral regurgitation (MR) is primarily caused by left ventricle deformation, but leaflet thickening with fibrotic changes are also observed in the valve. Increased levels of 5-hydroxytryptamine (5-HT; ie, serotonin) are described after myocardial infarction (MI); 5-HT can induce valve fibrosis through the 5-HT type 2B receptor (5-HT2BR).

OBJECTIVES

This study aims to test the hypothesis that post-MI treatment with cyproheptadine (5-HT2BR antagonist) can prevent ischemic MR by reducing the effect of serotonin on mitral biology.

METHODS

Thirty-six sheep were divided into 2 groups: inferior MI and inferior MI treated with cyproheptadine (0.5 mg/kg/d). Animals were followed for 90 days. Blood 5-HT, infarct size, left ventricular volume and function, MR fraction and mitral leaflet size were assessed. In a complementary in vitro study, valvular interstitial cells were exposed to pre-MI and post-MI serum collected from the experimental animals.

RESULTS

Increased 5-HT levels were observed after MI in nontreated animals, but not in the group treated with cyproheptadine. Infarct size was similar in both groups (11 ± 3 g vs 9 ± 5 g; P = 0.414). At 90 days, MR fraction was 16% ± 7% in the MI group vs 2% ± 6% in the cyproheptadine group (P = 0.0001). The increase in leaflet size following MI was larger in the cyproheptadine group (+40% ± 9% vs +22% ± 12%; P = 0.001). Mitral interstitial cells overexpressed extracellular matrix genes when treated with post-MI serum, but not when exposed to post-MI serum collected from treated animals.

CONCLUSIONS

Cyproheptadine given after inferior MI reduces post-MI 5-HT levels, prevents valvular fibrotic remodeling, is associated with larger increase in mitral valve size and less MR.

Elucidating the metabolic characteristics of pancreatic β-cells from patients with type 2 diabetes (T2D) using a genome-scale metabolic modeling

Diabetes is a global health problem caused primarily by the inability of pancreatic β-cells to secrete adequate insulin. Despite extensive research, the identity of factors contributing to the dysregulated metabolism-secretion coupling in the β-cells remains elusive. The present study attempts to capture some of these factors responsible for the impaired β-cell metabolism-secretion coupling that contributes to diabetes pathogenesis. The metabolic-flux profiles of pancreatic β-cells were predicted using genome-scale metabolic modeling for ten diabetic patients and ten control subjects. Analysis of these flux states shows reduction in the mitochondrial fatty acid oxidation and mitochondrial oxidative phosphorylation pathways, that leads to decreased insulin secretion in diabetes. We also observed elevated reactive oxygen species (ROS) generation through peroxisomal fatty acid β-oxidation. In addition, cellular antioxidant defense systems were found to be attenuated in diabetes. Our analysis also uncovered the possible changes in the plasma metabolites in diabetes due to the β-cells failure. These efforts subsequently led to the identification of seven metabolites associated with cardiovascular disease (CVD) pathogenesis, thus establishing its link as a secondary complication of diabetes.

Influence of Serotonin 5-HT4 Receptors on Responses to Cardiac Stressors in Transgenic Mouse Models

The current study aimed to deepen our knowledge on the role of cardiac 5-HT4 receptors under pathophysiological conditions. To this end, we used transgenic (TG) mice that overexpressed human 5-HT4a receptors solely in cardiac myocytes (5-HT4-TG mice) and their wild-type (WT) littermates that do not have functional cardiac 5-HT4 receptors as controls. We found that an inflammation induced by lipopolysaccharide (LPS) was detrimental to cardiac function in both 5-HT4-TG and WT mice. In a hypoxia model, isolated left atrial preparations from the 5-HT4-TG mice went into contracture faster during hypoxia and recovered slower following hypoxia than the WT mice. Similarly, using isolated perfused hearts, 5-HT4-TG mice hearts were more susceptible to ischemia compared to WT hearts. To study the influence of 5-HT4 receptors on cardiac hypertrophy, 5-HT4-TG mice were crossbred with TG mice overexpressing the catalytic subunit of PP2A in cardiac myocytes (PP2A-TG mice, a model for genetically induced hypertrophy). The cardiac contractility, determined by echocardiography, of the resulting double transgenic mice was attenuated like in the mono-transgenic PP2A-TG and, therefore, largely determined by the overexpression of PP2A. In summary, depending on the kind of stress put upon the animal or isolated tissue, 5-HT4 receptor overexpression could be either neutral (genetically induced hypertrophy, sepsis) or possibly detrimental (hypoxia, ischemia) for mechanical function. We suggest that depending on the underlying pathology, the activation or blockade of 5-HT4 receptors might offer novel drug therapy options in patients.

Effects of M-1, a Major Metabolite of Sarpogrelate, on 5-HT-Induced Constriction of Isolated Human Internal Thoracic Artery

Sarpogrelate, a selective 5-hydroxytryptamine (5-HT)_2A receptor antagonist, inhibits 5-HT-induced platelet aggregation and vasoconstriction. It improves ischemic symptoms in patients with arteriosclerosis obliterans. M-1 is a major metabolite of sarpogrelate, and has been reported to show a higher affinity for the 5-HT_2A receptor on platelets than sarpogrelate. However, the effects of M-1 on 5-HT-induced constrictive response in human blood vessels have not been investigated. The internal thoracic artery (ITA) is the key conduit for coronary artery bypass grafting (CABG). 5-HT has been implicated as playing an important role in the pathogenesis of vasospasm. Thus, in the present study, the effects of M-1 on 5-HT-induced vasoconstriction were examined in isolated human endothelium denuded ITA. M-1 inhibited 5-HT-induced vasoconstriction in a concentration-dependent manner. At the highest concentration, M-1 almost completely inhibited the 5-HT-induced vasoconstriction. Expression of 5-HT_2A and 5-HT_1B receptor proteins in the membrane fraction of ITA smooth muscle cells was confirmed by Western blot analysis. Individually, supramaximal concentrations of sarpogrelate and SB224289, a selective 5-HT_1B receptor antagonist, only partially inhibited the 5-HT-induced vasoconstriction. However, simultaneous pretreatment with both these antagonists almost completely inhibited the 5-HT-induced vasoconstriction. The inhibitory effect of M-1 pretreatment mimicked the inhibitory effect of simultaneous pretreatment with sarpogrelate and SB224289. These results suggest that M-1 has antagonistic effects not only on the 5-HT_2A receptor but also on the 5-HT_1B receptor in human ITA smooth muscle cells. M-1 may be useful as a lead compound for the development of drugs for the treatment of 5-HT-induced vasospasms in CABG.

Serotonin: a platelet hormone modulating cardiovascular disease

Cardiovascular diseases and depression are significant health burdens and increasing evidence suggests a causal relationship between them. The incidence of depression among patients suffering from cardiovascular disease is markedly elevated, and depression itself is an established cardiovascular risk factor. Serotonin 5-hydroxytryptamin (5-HT), a biogenic amine acting as a neurotransmitter and a peripheral hormone, is involved in the pathogenesis of both, cardiovascular disease and depression. Novel cardiovascular functions of 5-HT have recently been described and will be summarized in this review. 5-HT has a broad spectrum of functions in the cardiovascular system, yet the clinical or experimental data are partly conflicting. There is further research needed to characterize the clinical effects of 5-HT in particular tissues to enable targeted pharmacological therapies.

Dopamine in the Pathophysiology of Preeclampsia and Gestational Hypertension: Monoamine Oxidase (MAO) and Catechol-O-methyl Transferase (COMT) as Possible Mechanisms

Purpose of the Review

Hypertension in pregnancy is the global health burden. Amongst the hypertensive disorders of pregnancy, preeclampsia and gestational hypertension are the world's leading disorders that lead to both maternal and fetal morbidity and mortality.

Recent Findings

Dopamine inactive metabolites, namely, monoamine oxidase (MAO) and catechol-O-methyl transferase (COMT), have been reported to be associated with hypertensive disorders of pregnancy such preeclampsia and gestational hypertension.

Summary

This review discusses the involvement of MAO and COMT in the pathophysiology of both conditions in order to have a better understanding on the pathogenesis of both conditions, suggesting promising therapeutic interventions and subsequently reducing maternal and fetal morbidity and mortality.

Inhibition of 5-Hydroxytryptamine Receptor 2B Reduced Vascular Restenosis and Mitigated the β-Arrestin2-Mammalian Target of Rapamycin/p70S6K Pathway

BACKGROUND

As a monoamine neurotransmitter, 5-hydroxytryptamine (5-HT) or serotonin modulates mood, appetite, and sleep. Besides, 5-HT also has important peripheral functions. 5-HT receptor 2B (5-HT2BR) plays a key role in cardiovascular diseases, such as pulmonary arterial hypertension and cardiac valve disease. Percutaneous intervention has been used to restore blood flow in occlusive vascular disease. However, restenosis remains a significant problem. Herein, we investigated the role of 5-HT2BR in neointimal hyperplasia, a key pathological process in restenosis.

METHODS AND RESULTS

The expression of 5-HT2BR was upregulated in wire-injured mouse femoral arteries. In addition, BW723C86, a selective 5-HT2BR agonist, promoted the injury response during restenosis. 5-HT and BW723C86 stimulated migration and proliferation of rat aortic smooth muscle cells. Conversely, LY272015, a selective antagonist, attenuated the 5-HT-induced smooth muscle cell migration and proliferation. In vitro study showed that the promigratory effects of 5-HT2BR were mediated through the activation of mammalian target of rapamycin (mTOR)/p70S6K signaling in a β-arrestin2-dependent manner. Inhibition of mammalian target of rapamycin or p70S6K mitigated 5-HT2BR-mediated smooth muscle cell migration. Mice with deficiency of 5-HT2BR showed significantly reduced neointimal formation in wire-injured arteries.

CONCLUSIONS

These results demonstrated that activation of 5-HT2BR and β-arrestin2-biased downstream signaling are key pathological processes in neointimal formation, and 5-HT2BR may be a potential target for the therapeutic intervention of vascular restenosis.

Analysis of Serotonin Molecules on Silver Nanocolloids-A Raman Computational and Experimental Study

Combined theoretical and experimental analysis of serotonin by quantum chemical density functional calculations and surface-enhanced Raman spectroscopy, respectively, is presented in this work to better understand phenomena related to this neurotransmitter’s detection and monitoring at very low concentrations specific to physiological levels. In addition to the successful ultrasensitive analyte detection on silver nanoparticles for concentrations as low as 10⁻¹¹ molar, the relatively good agreement between the simulated and experimentally determined results indicates the presence of all serotonin molecular forms, such as neutral, ionic, and those oxidized through redox reactions. Obvious structural molecular deformations such as bending of lateral amino chains are observed for both ionic and oxidized forms. Not only does this combined approach reveal more probable adsorption of serotonin into the silver surface through hydroxyl/oxygen sites than through NH/nitrogen sites, but also that it does so predominantly in its neutral (reduced) form, somewhat less so in its ionic forms, and much less in its oxidized forms. If the development of opto-voltammetric biosensors and their effective implementation is envisioned for the future, this study provides some needed scientific background for comprehending changes in the vibrational signatures of this important neurotransmitter.

Protective effects of fluvoxamine against ischemia/reperfusion injury in isolated, perfused guinea-pig hearts

Serotonin (5-hydroxytryptamine; 5-HT) is known to be activated during ischemia-reperfusion and triggers contractile dysfunction and pathological apoptosis. Here, the beneficial effects of the selective serotonin reuptake inhibitor (SSRI) fluvoxamine was demonstrated on ischemia-reperfusion injury in guinea-pig hearts perfused using the Langendorff technique. The recovery (%) of left ventricular developed pressure (LVDP) by fluvoxamine (5×10(-8) M) was 95.4% (control: 32%), which was consistent with the inhibition of mitochondrial Ca(2+)([Ca(2+)]m) uptake induced by changes in the Ca(2+) content and acidification of the perfusate, and similar to reperfusion following global ischemia in Langendorff-perfused hearts. Fluvoxamine inhibited the increase in [Ca(2+)]m induced by changes in the Ca(2+) content of the perfusate in perfused preparations of mitochondria, which was similar to the results obtained with the mitochondrial permeability transition pore (MPTP) opener atractyroside. The terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end labeling (TUNEL)-positive cells were significantly less in fluvoxamine-treated hearts than in control hearts, with decreases in caspase-3 activity. These results suggest that SSRI inhibits opening of the MPTP by preventing [Ca(2+)]m overload-induced apoptosis related to the endogenous accumulation of 5-HT in ischemia-reperfusion hearts.

A serotonin-induced N-glycan switch regulates platelet aggregation

Serotonin (5-HT) is a multifunctional signaling molecule that plays different roles in a concentration-dependent manner. We demonstrated that elevated levels of plasma 5-HT accelerate platelet aggregation resulting in a hypercoagulable state in which the platelet surface becomes occupied by several glycoproteins. Here we study the novel hypothesis that an elevated level of plasma 5-HT results in modification of the content of N-glycans on the platelet surface and this abnormality is associated with platelet aggregation. Mass spectrometry of total surface glycoproteins on platelets isolated from wild-type mice infused for 24 hours with saline or 5-HT revealed that the content of glycoproteins on platelets from 5-HT-infused mice switched from predominantly N-acetyl-neuraminic acid (Neu5Ac) to N-glycolyl-neuraminic acid (Neu5Gc). Cytidine monophosphate-N-acetylneuraminate hydroxylase (CMAH) synthesizes Neu5Gc from Neu5Ac. Up-regulation of Neu5Gc content on the platelet surface resulted from an increase in the catalytic function, not expression, of CMAH in platelets of 5-HT-infused mice. The highest level of Neu5Gc was observed in platelets of 5-HT-infused, 5-HT transporter-knock out mice, suggesting that the surface delineated 5-HT receptor on platelets may promote CMAH catalytic activity. These new findings link elevated levels of plasma 5-HT to altered platelet N-glycan content, a previously unrecognized abnormality that may favor platelet aggregation.

Impact of elevated plasma serotonin on global gene expression of murine megakaryocytes

Background

Serotonin (5-HT) is a biogenic amine that also acts as a mitogen and a developmental signal early in rodent embryogenesis. Genetic and pharmacological disruption of 5-HT signaling causes various diseases and disorders via mediating central nervous system, cardiovascular system, and serious abnormalities on a growing embryo. Today, neither the effective modulators on 5-HT signaling pathways nor the genes affected by 5-HT signal are well known yet.

Methodology/Principal Findings

In an attempt to identify the genes altered by 5-HT signaling pathways, we analyzed the global gene expression via the Illumina array platform using the mouse WG-6 v2.0 Expression BeadChip containing 45,281 probe sets representing 30,854 genes in megakaryocytes isolated from mice infused with 5-HT or saline. We identified 723 differentially expressed genes of which 706 were induced and 17 were repressed by elevated plasma 5-HT.

Conclusions/Significance

Hierarchical gene clustering analysis was utilized to represent relations between groups and clusters. Using gene ontology mining tools and canonical pathway analyses, we identified multiple biological pathways that are regulated by 5-HT: (i) cytoskeletal remodeling, (ii) G-protein signaling, (iii) vesicular transport, and (iv) apoptosis and survival. Our data encompass the first extensive genome-wide based profiling in the progenitors of platelets in response to 5-HT elevation in vivo.

Serotonin: from top to bottom

Serotonin is a monoamine neurotransmitter, which is phylogenetically conserved in a wide range of species from nematodes to humans. In mammals, age-related changes in serotonin systems are known risk factors of age-related diseases, such as diabetes, faecal incontinence and cardiovascular diseases. A decline in serotonin function with aging would be consistent with observations of age-related changes in behaviours, such as sleep, sexual behaviour and mood all of which are linked to serotonergic function. Despite this little is known about serotonin in relation to aging. This review aims to give a comprehensive analysis of the distribution, function and interactions of serotonin in the brain; gastrointestinal tract; skeletal; vascular and immune systems. It also aims to demonstrate how the function of serotonin is linked to aging and disease pathology in these systems. The regulation of serotonin via microRNAs is also discussed, as are possible applications of serotonergic drugs in aging research and age-related diseases. Furthermore, this review demonstrates that serotonin is potentially involved in whole organism aging through its links with multiple organs, the immune system and microRNA regulation. Methods to investigate these links are discussed.

The cardiac ventricular 5-HT4 receptor is functional in late foetal development and is reactivated in heart failure

A positive inotropic responsiveness to serotonin, mediated by 5-HT₄ and 5-HT_2A receptors, appears in the ventricle of rats with post-infarction congestive heart failure (HF) and pressure overload-induced hypertrophy. A hallmark of HF is a transition towards a foetal genotype which correlates with loss of cardiac functions. Thus, we wanted to investigate whether the foetal and neonatal cardiac ventricle displays serotonin responsiveness. Wistar rat hearts were collected day 3 and 1 before expected birth (days -3 and -1), as well as day 1, 3, 5 and 113 (age matched with Sham and HF) after birth. Hearts from post-infarction HF and sham-operated animals (Sham) were also collected. Heart tissue was examined for mRNA expression of 5-HT₄, 5-HT_2A and 5-HT_2B serotonin receptors, 5-HT transporter, atrial natriuretic peptide (ANP) and myosin heavy chain (MHC)-α and MHC-β (real-time quantitative RT-PCR) as well as 5-HT-receptor-mediated increase in contractile function exvivo (electrical field stimulation of ventricular strips from foetal and neonatal rats and left ventricular papillary muscle from adult rats in organ bath). Both 5-HT₄ mRNA expression and functional responses were highest at day -3 and decreased gradually to day 5, with a further decrease to adult levels. In HF, receptor mRNA levels and functional responses reappeared, but to lower levels than in the foetal ventricle. The 5-HT_2A and 5-HT_2B receptor mRNA levels increased to a maximum immediately after birth, but of these, only the 5-HT_2A receptor mediated a positive inotropic response. We suggest that the 5-HT₄ receptor is a representative of a foetal cardiac gene program, functional in late foetal development and reactivated in heart failure.

Down-regulation of the serotonin transporter in hyperreactive platelets counteracts the pro-thrombotic effect of serotonin

An elevated plasma concentration of serotonin ([5-HT]) is a common feature of cardiovascular disease often associated with enhanced platelet activation and thrombosis. Whether elevated in vivo plasma 5-HT per se represents an independent risk factor for platelet hyperreactivity or only is an epiphenomenon of cardiovascular disease is poorly understood. We examined in vitro and in vivo platelet function following a 24h elevation of plasma [5-HT] in mice. In vivo administration of 5-HT using osmotic minipumps increased plasma [5-HT] in treated mice compared to control mice instrumented with saline loaded pumps. 5-HT infusion did not increase systolic blood pressure, but markers of platelet activation including P-selectin and (PE)Jon/A staining were increased and these findings coincided with the enhanced aggregation of isolated platelets in response to type I fibrillar collagen. Tail bleeding times and the time to occlusion following chemical damage to the carotid artery were shortened in 5-HT-infused mice. 5-HT-infused mice were treated with paroxetine (Prx) to block 5-HT uptake via the serotonin transporter (SERT). Prx lowered platelet [5-HT] and attenuated platelet activation and aggregation. These results and our biochemical indices of enhanced 5-HT intracellular signaling in the platelets of 5-HT-infused mice reveal a mechanistic link between elevated plasma [5-HT], abnormal intracellular 5-HT signaling and accentuated platelet aggregation. Although a down-regulation of the serotonin transporter (SERT) on the platelet surface may counteract the pro-thrombotic influence of elevated plasma [5HT], this compensatory mechanism may fail to prevent the increased thrombotic risk caused by elevated plasma [5-HT].

Mechanism of sarpogrelate action in improving cardiac function in diabetes

Although sarpogrelate, a 5-HT(2A) receptor antagonist, has been reported to exert beneficial effects in diabetes, the mechanisms of its action are not understood. In this study, diabetes was induced in rats by an injection of streptozotocin (65 mg/kg) and the animals were assessed 7 weeks later. Decreased serum insulin as well as increased serum glucose, cholesterol, and triglyceride levels in diabetic animals were associated with increased blood pressure and heart/body weight ratio. Impaired cardiac performance in diabetic animals was evident by decreased heart rate, left ventricular developed pressure, rate of pressure development, and rate of pressure decay. Treatment of diabetic animals with sarpogrelate (5 mg/kg) or insulin (10 units/kg) daily for 6 weeks attenuated the observed changes in serum insulin, glucose, and lipid levels as well as blood pressure and cardiac function by varying degrees. Protein content for membrane glucose transporters (GLUT-1 and GLUT-4) was depressed in diabetic heart; the observed alteration in GLUT-4 was partially prevented by both sarpogrelate and insulin, whereas that in GLUT-1 was attenuated by sarpogrelate only. Incubation of myoblast cells with sarpogrelate and insulin stimulated glucose uptake; these effects were additive. 5-hydroxytryptamine was found to inhibit glucose-induced insulin release from the pancreas; this effect was prevented by sarpogrelate. These results suggest that sarpogrelate may improve cardiac function in chronic diabetes by promoting the expression of membrane glucose transporters as well as by releasing insulin from the pancreas.

Molecular mechanisms of SERT in platelets: regulation of plasma serotonin levels

The serotonin transporter (SERT) on platelets is a primary mechanism for serotonin (5HT) uptake from the blood plasma. Alteration in plasma 5HT level is associated with a number of cardiovascular diseases and disorders. Therefore, the regulation of the transporter's activity represents a key mechanism to stabilize the concentration of plasma 5HT. There is a biphasic relationship between plasma 5HT elevation, loss of surface SERT, and depletion of platelet 5HT. Specifically, in platelets, plasma membrane SERT levels and platelet 5HT uptake initially rise as plasma 5HT levels are increased but then fall below normal as the plasma 5HT level continues to rise. Therefore, we propose that elevated plasma 5HT limits its own uptake in platelets by down-regulating SERT as well as modifying the characteristics of SERT partners in the membrane trafficking pathway. This review will summarize current findings regarding the biochemical mechanisms by which elevated 5HT downregulates the expression of SERT on the platelet membrane. Intriguing aspects of this regulation include the intracellular interplay of SERT with the small G protein Rab4 and the concerted 5HT-mediated phosphorylation of vimentin.

Regulation of cardiac afferent excitability in ischemia

The heart at the time of Sir William Harvey originally was thought to be an insensate organ. Today, however, we know that this organ is innervated by sensory nerves that course centrally though mixed nerve pathways that also contain parasympathetic or sympathetic motor nerves. Angina or cardiac pain is now well recognized as a pressure-like pain that occurs during myocardial ischemia when coronary artery blood flow is interrupted. Sympathetic (or spinal) afferent fibers that are either finely myelinated or unmyelinated are responsible for the transmission of information to the brain that ultimately allows the perception of angina as well as activation of the sympathetic nervous system, resulting in tachycardia, hypertension, and sometimes arrhythmias. Although early studies defined the importance of the vagal and sympathetic cardiac afferent systems in reflex autonomic control, until recently there has been little appreciation of the mechanisms of activation of the sensory endings. This review examines the role of a number of chemical mediators and their sources that are activated by the ischemic process. In this regard, patients with ischemic syndromes, particularly myocardial infarction and unstable angina, are known to have platelet activation, which leads to release of a number of chemical mediators, including serotonin, histamine, and thromboxane A(2), all of which stimulate ischemically sensitive cardiac spinal afferent endings in the ventricles through specific receptor-mediated processes. Furthermore, protons from lactic acid, bradykinin, and reactive oxygen species, especially hydroxyl radicals, individually and frequently in combination, stimulate these endings during ischemia. Cyclooxygenase products appear to sensitize the endings to the action of bradykinin and histamine. These studies of the chemical mechanisms of activation of cardiac sympathetic afferent endings during ischemia have the potential to provide targeted therapies that can modify the angina and the deleterious reflex responses that have the potential to exacerbate ischemia and myocardial cell death.

Serotonin induces vasoconstriction of smooth muscle cell-rich neointima through 5-hydroxytryptamine2A receptor in rabbit femoral arteries

BACKGROUND

Smooth muscle cell (SMC)-rich intima is a morphological feature of atherosclerotic lesions that is observed in eroded plaque and spastic arteries. Arteries with SMC-rich intima are susceptible to vasoconstriction or vasospasm against some vasoactive agents.

OBJECTIVE

The present study evaluates the contribution of SMC-rich intima to thrombogenic vasoconstriction.

METHODS

We established SMC-rich neointima by damaging rabbit femoral arteries using balloons and then measured the isometric tension of the femoral strips against 5-hydroxytryptamine (5-HT), adenosine diphosphate, adenosine triphosphate and thrombin.

RESULTS

Among these agents, only 5-HT induced a hypercontractile response of the injured arteries with SMC-rich neointima, compared with non-injured arteries. Smooth muscle cells of both the neointima and media expressed 5-HT(2A) receptor, and sarpogrelate, a selective 5-HT(2A) receptor antagonist significantly inhibited the hypercontraction. Furthermore, 5-HT induced contraction of separated neointima and hypercontraction of separated media compared with non-injured media. Sarpogrelate and fasudil, a specific Rho-kinase inhibitor, significantly suppressed such contraction of both the neointima and media of injured arteries.

CONCLUSIONS

These results suggest that 5-HT plays a crucial role in thrombogenic vasoconstriction, and that SMC-rich intima as well as media directly contributes to the hypercontractile response of atherosclerotic vessels through the 5-HT(2A) receptor and the Rho-kinase pathway.

Regulation of Coronary Blood Flow During Exercise

Exercise is the most important physiological stimulus for increased myocardial oxygen demand. The requirement of exercising muscle for increased blood flow necessitates an increase in cardiac output that results in increases in the three main determinants of myocardial oxygen demand: heart rate, myocardial contractility, and ventricular work. The approximately sixfold increase in oxygen demands of the left ventricle during heavy exercise is met principally by augmenting coronary blood flow (∼5-fold), as hemoglobin concentration and oxygen extraction (which is already 70–80% at rest) increase only modestly in most species. In contrast, in the right ventricle, oxygen extraction is lower at rest and increases substantially during exercise, similar to skeletal muscle, suggesting fundamental differences in blood flow regulation between these two cardiac chambers. The increase in heart rate also increases the relative time spent in systole, thereby increasing the net extravascular compressive forces acting on the microvasculature within the wall of the left ventricle, in particular in its subendocardial layers. Hence, appropriate adjustment of coronary vascular resistance is critical for the cardiac response to exercise. Coronary resistance vessel tone results from the culmination of myriad vasodilator and vasoconstrictors influences, including neurohormones and endothelial and myocardial factors. Unraveling of the integrative mechanisms controlling coronary vasodilation in response to exercise has been difficult, in part due to the redundancies in coronary vasomotor control and differences between animal species. Exercise training is associated with adaptations in the coronary microvasculature including increased arteriolar densities and/or diameters, which provide a morphometric basis for the observed increase in peak coronary blood flow rates in exercise-trained animals. In larger animals trained by treadmill exercise, the formation of new capillaries maintains capillary density at a level commensurate with the degree of exercise-induced physiological myocardial hypertrophy. Nevertheless, training alters the distribution of coronary vascular resistance so that more capillaries are recruited, resulting in an increase in the permeability-surface area product without a change in capillary numerical density. Maintenance of α- and ß-adrenergic tone in the presence of lower circulating catecholamine levels appears to be due to increased receptor responsiveness to adrenergic stimulation. Exercise training also alters local control of coronary resistance vessels. Thus arterioles exhibit increased myogenic tone, likely due to a calcium-dependent protein kinase C signaling-mediated alteration in voltage-gated calcium channel activity in response to stretch. Conversely, training augments endothelium-dependent vasodilation throughout the coronary microcirculation. This enhanced responsiveness appears to result principally from an increased expression of nitric oxide (NO) synthase. Finally, physical conditioning decreases extravascular compressive forces at rest and at comparable levels of exercise, mainly because of a decrease in heart rate. Impedance to coronary inflow due to an epicardial coronary artery stenosis results in marked redistribution of myocardial blood flow during exercise away from the subendocardium towards the subepicardium. However, in contrast to the traditional view that myocardial ischemia causes maximal microvascular dilation, more recent studies have shown that the coronary microvessels retain some degree of vasodilator reserve during exercise-induced ischemia and remain responsive to vasoconstrictor stimuli. These observations have required reassessment of the principal sites of resistance to blood flow in the microcirculation. A significant fraction of resistance is located in small arteries that are outside the metabolic control of the myocardium but are sensitive to shear and nitrovasodilators. The coronary collateral system embodies a dynamic network of interarterial vessels that can undergo both long- and short-term adjustments that can modulate blood flow to the dependent myocardium. Long-term adjustments including recruitment and growth of collateral vessels in response to arterial occlusion are time dependent and determine the maximum blood flow rates available to the collateral-dependent vascular bed during exercise. Rapid short-term adjustments result from active vasomotor activity of the collateral vessels. Mature coronary collateral vessels are responsive to vasodilators such as nitroglycerin and atrial natriuretic peptide, and to vasoconstrictors such as vasopressin, angiotensin II, and the platelet products serotonin and thromboxane A2. During exercise, ß-adrenergic activity and endothelium-derived NO and prostanoids exert vasodilator influences on coronary collateral vessels. Importantly, alterations in collateral vasomotor tone, e.g., by exogenous vasopressin, inhibition of endogenous NO or prostanoid production, or increasing local adenosine production can modify collateral conductance, thereby influencing the blood supply to the dependent myocardium. In addition, vasomotor activity in the resistance vessels of the collateral perfused vascular bed can influence the volume and distribution of blood flow within the collateral zone. Finally, there is evidence that vasomotor control of resistance vessels in the normally perfused regions of collateralized hearts is altered, indicating that the vascular adaptations in hearts with a flow-limiting coronary obstruction occur at a global as well as a regional level. Exercise training does not stimulate growth of coronary collateral vessels in the normal heart. However, if exercise produces ischemia, which would be absent or minimal under resting conditions, there is evidence that collateral growth can be enhanced. In addition to ischemia, the pressure gradient between vascular beds, which is a determinant of the flow rate and therefore the shear stress on the collateral vessel endothelium, may also be important in stimulating growth of collateral vessels.

Sumatriptan provokes coronary artery spasm in patients with variant angina: Possible involvement of serotonin 1B receptor

BACKGROUND

Serotonin (5HT) can induce coronary artery spasm (CAS) in patients with variant angina (VA). We have previously reported that 5HT(1B) and 5HT(2A) receptors gene were expressed in human coronary arterial smooth muscle cells and that isolated coronary artery from a patient with VA showed the supersensitivity to sumatriptan (SMT), a 5HT(1B/1D) receptor agonist. The aim of the present study was to determine whether SMT can provoke CAS directly or indirectly through platelet aggregation in patients with VA.

METHODS

We evaluated the effects of intracoronary infusion of graded concentrations of SMT on coronary arteries in 9 patients, including 5 documented VA and 4 participants with atypical chest pain as control.

RESULTS

SMT provoked CAS in all patients with VA. SMT could not induce CAS in control. SMT (10(-4) M) caused significant contractions (%diameter of baseline; median [interquartile range], 0 [0-18.4]% in VA, as compared with control (proximal segments; 92.6 [77.9-118.9]%, p<0.05 vs. VA, distal segments; 92.9 [65.3-158.5]%, p<0.01 vs. VA). In control, minor dilation occurred at SMT concentration up to 10(-5) M. SMT could induce in vitro platelet aggregation neither in healthy subjects nor in patients with VA.

CONCLUSIONS

These findings suggest that activation of 5HT(1B) receptor by SMT can induce CAS directly in patients with VA without platelet activation. This is the first report directly demonstrating the effect of 5HT(1B) receptor activation on human coronary arteries in vivo.

Sarpogrelate, a specific 5HT2-receptor antagonist, improves the coronary microcirculation in coronary artery disease

BACKGROUND

Serotonin (5-hydroxytryptamine: 5-HT) reduces the coronary blood flow (CBF) as a product of aggregating platelets. Sarpogrelate, a specific 5HT2-receptor antagonist, has been reported to increase the coronary collateral flow in humans: however, its effect on the microcirculation is still not fully understood.

HYPOTHESIS

This study was undertaken to determine whether sarpogrelate might improve the microcirculation in coronary artery disease (CAD).

METHODS

To investigate the effect of sarpogrelate on the microcirculation in CAD, we measured CBF in 15 patients with CAD but no significant stenosis in the left anterior descending artery (LAD). The patients were randomly allocated to two groups, including those receiving oral administration of 200 mg of sarpogrelate (SPG, 8 patients, age 61 +/- 6 years) and those receiving no medication (controls, 7 patients, age 57 +/- 8 years). Prior to and 1 h after the administration of sarpogrelate, or in controls at 1-h intervals, the average peak velocity (APV) at baseline and hyperemia was measured by an intracoronary Doppler guidewire. Systemic blood pressure (SBP) and cardiac output (CO) were also measured.

RESULTS

In the patients receiving SPG, the medication significantly increased the baseline (18 +/- 9 to 19 +/- 10 cm/s, p < 0.05) and maximal APV (55 +/- 9 to 64 +/- 31 cm/s, p<0.05). However, no significant changes were observed in SBP and CO after the administration of SPG. In the control group, there were no significant differences in baseline and hyperemic APV.

CONCLUSION

Sarpogrelate increased both baseline and maximal CBF without changing the systemic hemodynamics. These findings thus support that SPG improves the microcirculation by antagonizing the vasoconstrictive products of the aggregating platelets in CAD.

Determinants of Ischemic Mitral Regurgitation in Patients with Chronic Anterior Wall Myocardial Infarction: A Real Time Three-Dimensional Echocardiography Study

OBJECTIVE

We sought to elucidate the geometric determinants of ischemic mitral regurgitation (IMR) in patients with chronic anterior myocardial infarction (MI).

MATERIALS AND METHODS

In 16 patients with anterior MI only (Group A) and 18 patients with both anterior and inferoposterior MI (Group B), three parallel equidistant anteroposterior (AP) planes (medial, central, lateral) perpendicular to the mitral valvular commissure-commissure plane were generated. The systolic tenting area of the mitral valve (MVTa) and the angles between the annular plane and leaflets (anterior, Aalpha; posterior, Palpha) on the AP planes were measured. The left ventricular end-systolic and end-diastolic volumes, and end-diastolic and end-systolic mitral annular area (MAAs) were obtained.

RESULT

The regurgitant orifice area (ROA) was significantly smaller in Group A than Group B (0.08 +/- 0.09 vs 0.20 +/- 0.18 cm(2), P < 0.05). In the total of 34 patients, the medial MVTa (P < 0.001), MAAs (P < 0.05) and the spherical index (P < 0.05) were three independent determinants of ROA while the left ventricular volumes were not. MAAs was the only independent determinant of ROA in Group A, while the medial MVTa was in Group B. Palpha (P < 0.05) and MVTa (P = 0.06) tended to be larger in the medial than the lateral side in Group B, while no differences were found in Group A.

CONCLUSION

The geometry of the mitral valve apparatus was more important than the left ventricular volumes in determining the severity of IMR in patients with anterior MI. The posteromedial side tenting could play a critical role in causing significant IMR when the inferoposterior MI coexists with anterior MI.

5-HT2 receptor blocker sarpogrelate prevents downregulation of antiapoptotic protein Bcl-2 and protects the heart against ischemia–reperfusion injury

Even though reperfusion is the treatment of choice in patients admitted with acute myocardial infarction, reperfusion itself has been demonstrated to activate various pathological factors especially following procedures of cardiac revascularization. 5-hydroxytryptamine (5HT) is one such factor activated during reperfusion and is known to trigger the post ischemic contractile dysfunction and pathological apoptosis. Here we demonstrate the potential effects of the 5-HT(2)A antagonist sarpogrelate in protecting the myocardium against reperfusion injury of heart. Male Wistar rats weighing between 220 and 240 g were subjected to 30 min left coronary artery (LCA) occlusion and 120 min reperfusion. Sarpogrelate (4 mg/kg) was infused intravenously for 30 min either before LCA occlusion or at reperfusion. Following reperfusion the samples were collected for infarction area, immunohistochemistry, western blotting and myocardial metabolite analysis. Sarpogrelate infusion before ischemia resulted in (a) significant recovery of post ischemic cardiac functions (LVDP, EDP), (b) significant reduction in the infarct size among the risk area after triphenyl tetrazolium chloride staining (p<0.001), (c) decreased tissue water content (p<0.05), (d) well preserved myocardial ATP (p<0.05), (e) reduction in Bcl-2 downregulation and caspase 3 activation and (g) less prevalence of apoptotic cells (3.1+/-0.4% to 15.2+/-0.6%, drug versus control). Treating the rats with sarpogrelate during reperfusion also showed similar results. This study thus demonstrates the protective effects of sarpogrelate and supports the role for 5-HT2A inhibition in preventing the reperfusion injury of the heart.

5-Hydroxytryptamine receptors in the human cardiovascular system

The human cardiovascular system is exposed to plasma 5-hydroxytryptamine (5-HT, serotonin), usually released from platelets. 5-HT can produce harmful acute and chronic effects. The acute cardiac effects of 5-HT consist of tachycardia (preceded on occasion by a brief reflex bradycardia), increased atrial contractility and production of atrial arrhythmias. Acute inotropic, lusitropic and arrhythmic effects of 5-HT on human ventricle become conspicuous after inhibition of phosphodiesterase (PDE) activity. Human cardiostimulation is mediated through 5-HT4 receptors. Atrial and ventricular PDE3 activity exerts a protective role against potentially harmful cardiostimulation. Chronic exposure to high levels of 5-HT (from metastatic carcinoid tumours), the anorectic drug fenfluramine and its metabolites, as well as the ecstasy drug 3,4-methylenedioxymethamphetamine (MDMA) and its metabolite 3,4-methylenedioxyamphetamine (MDA) are associated with proliferative disease and thickening of cardiac valves, mediated through 5-HT2B receptors. 5-HT2B receptors have an obligatory physiological role in murine cardiac embryology but whether this happens in humans requires research. Congenital heart block (CHB) is, on occasion, associated with autoantibodies against 5-HT4 receptors. Acute vascular constriction by 5-HT is usually shared by 5-HT1B and 5-HT2A receptors, except in intracranial arteries which constrict only through 5-HT1B receptors. Both 5-HT1B and 5-HT2A receptors can mediate coronary artery spasm but only 5-HT1B receptors appear involved in coronary spasm of patients treated with triptans or with Prinzmetal angina. 5-HT2A receptors constrict the portal venous system including oesophageal collaterals in cirrhosis. Chronic exposure to 5-HT can contribute to pulmonary hypertension through activation of constrictor 5-HT1B receptors and proliferative 5-HT2B receptors, and possibly through direct intracellular effects.

Inhibition of 5-hydroxytryptamine receptor prevents occlusive thrombus formation on neointima of the rabbit femoral artery

BACKGROUND

Thrombus propagation on disrupted plaque is a major cause of acute coronary events and serious complication after coronary intervention. 5-Hydroxytryptamine (5-HT) is a potent vasoactive and platelet-aggregating substance that is predominantly mediated by 5-HT2A receptor. However, the roles of 5-HT2A receptor in occlusive thrombus formation on disrupted plaque remain obscure.

OBJECTIVE

We investigated the role of 5-HT2A receptor in thrombus formation using a rabbit model of repeated balloon-injury.

METHODS

Three weeks after a first balloon-injury of the femoral arteries, luminal diameter, neointimal growth, and vasoconstriction by 5-HT in vitro were examined. Thrombus propagation and the role of 5-HT2A receptor after a second balloon-injury were evaluated using sarpogrelate, a selective 5-HT2A receptor antagonist.

RESULTS

Three weeks after the first balloon-injury, luminal stenosis was evident in the femoral arteries, where the neointima expressed tissue factor and 5-HT2A receptor. The hypercontractile response of the stenotic arteries to 5-HT was significantly reduced by sarpogrelate. Balloon-injury of the neointima with substantially reduced blood flow promoted the formation of occlusive thrombus that was immunoreactive against glycoprotein IIb-IIIa, 5-HT2A receptor and fibrin. Intravenous injection of sarpogrelate significantly inhibited ex vivo platelet aggregation induced by adenosine 5'-diphosphate, thrombin and collagen alone as well as with 5-HT, and significantly prevented occlusive thrombus formation in vivo.

CONCLUSIONS

The 5-HT2A receptor appears to play a crucial role in occlusive thrombus formation in diseased arteries via platelet aggregation and vasoconstriction. Inhibition of 5-HT2A receptor might help reduce the onset of acute coronary events and of acute coronary occlusion after the intervention.

Comparison of plasma serotonin levels in patients with variant angina pectoris versus healed myocardial infarction

Patients with variant angina pectoris showed greater serotonin plasma levels than did control subjects and patients with healed myocardial infarction. The levels also tended to be greater in those with >1 episode/month than in those with fewer episodes. Moreover, patients with variant angina pectoris also had greater levels of nitrite and nitrate plasma levels than did control subjects or patients with healed myocardial infarction, partly, perhaps, as a compensatory mechanism.

Protective effects of sarpogrelate, a 5-HT2A antagonist, against postischemic myocardial dysfunction in guinea-pig hearts

The protective effects of sarpogrelate (SG), a 5-HT2A antagonist, were investigated in perfused guinea-pig Langendorff hearts subjected to ischemia and reperfusion. Changes in cellular levels of high phosphorous energy, NO and Ca2+ in the heart together with simultaneous recordings of left ventricular developed pressure (LVDP) were monitored using an nitric oxide (NO) electrode, fluorometry and 31P-NMR. The recovery of LVDP from ischemia by reperfusion was 30.1% in the control, while the treatment with SG (5 x 10(-7) M) in pre- and post-ischemia hearts produced a gradual increase to 73.1 and 53.6%, respectively. At the final stage of ischemia, the intracellular concentration of Ca2+ ([Ca2+]i) and release of NO increased with no twitching and remained at a high steady level. The addition of SG increased the transient NO signal (TNO) level at the end of ischemia compared with the control, but [Ca2+]i during ischemia decreased. Meanwhile, mitochondrial Ca2+ uptake on acidification or Ca2+ content changes of the perfusate was suppressed by pre-treatment with SG or the KATP channel opener diazoxide, but not the KATP channel blocker 5-HD. The myocardial NO elevated with 5-HT in normal Langendorff hearts was suppressed by the treatment with SG. Therefore, the existence of the 5HT2A receptor in a Langendorff heart was anticipated. By in vitro EPR, SG was found to directly quench the hydroxy radical. Thus, these findings suggested that the 5-HT2A receptor induced in ischemia-reperfusion plays an important role in the mitochondrial KATP channel of hearts in close relation with NO and active oxygen radicals.

Effect of the Serotonin Blocker Sarpogrelate on Circulating Interleukin-18 Levels in Patients with Diabetes and Arteriosclerosis Obliterans

We aimed to evaluate the effect of treatment with sarpogrelate, a serotonin 2A receptor antagonist, on circulating interleukin (IL)-18 levels in patients with diabetes and arteriosclerosis obliterans. Patients received sarpogrelate (100 mg 3 times daily) for 2 months. We evaluated the degree of cryaesthesia (a feeling of cold in the foot and toes) as the clinical outcome, and measured circulating IL-18, IL-6 and lipid protein concentrations. An improvement in clinical outcome occurred after initiation of sarpogrelate therapy;a significant decrease in IL-18 levels was observed after 2 months of therapy. Levels of IL-6 and lipid proteins, including triglyceride, total cholesterol and high-density lipoprotein cholesterol, were not significantly altered by treatment. Our data suggest that by reducing circulating IL-18 levels, sarpogrelate treatment may contribute to the inhibition of arteriosclerosis obliterans progression in patients with diabetes.

Eccentric Dosing of Nitrates Does Not Increase Cardiac Events in Patients with Healed Myocardial Infarction

This study was performed to investigate the risk of cardiac events by eccentric or continuous dosing of nitrates in patients with healed myocardial infarction. A total of 573 patients with healed myocardial infarction were assigned to one of two groups: a nitrate-treatment (n =239) and a nontreatment (n =334) group. The nitrate-treatment group was further subdivided into a group receiving eccentric dosing of nitrates (n =153) and a group receiving continuous dosing of nitrates (n =86). The mean observation period was 11.2+/-8.2 months. The cardiac events investigated were nonfatal and fatal recurrent myocardial infarction, death from congestive heart failure, sudden death, worsening angina and rebound angina. Baseline characteristics were also compared among the three groups to determine any effects on outcome. Among the patients receiving eccentric or continuous dosing of nitrates, the rates of cardiac events were 12.7/1,000 person.year and 67.4/1,000 person.year, respectively, whereas the rate was 19.7/1,000 person.year in the nontreated patients. The incidence of cardiac events was significantly greater in patients receiving continuous dosing of nitrates than in the nontreated patients (p <0.05). Continuous dosing of nitrates thus increases cardiac events, and while eccentric dosing of nitrates does not increase them, it is also not effective at preventing them in patients with healed myocardial infarction.

Bimodality of cardiac vagal afferent C-fibres in the rat

Vagal afferent C-fibres from the heart constitute an important input to the neurogenic cardiovascular regulation. These fibres respond to altered cardiac filling pressures and to chemical stimuli. In rats, we tested whether cardiac vagal afferent C-fibres react exclusively to one stimulus (chemical or mechanical) or whether the fibres are bimodal, i.e. responsive to either kind of stimulus. As a mechanical stimulus, an indwelling balloon was inflated in the aorta to increase left ventricular end-diastolic pressure. The serotonin 5HT(3) receptor agonist phenylbiguanide was injected into the pericardial sac as a chemical stimulus. An increase of fibre activity by more than two standard deviations compared with control was considered a response to a stimulus. Most fibres (42 out of 57) responded to both stimuli and were categorized as bimodal, 9 fibres were solely mechanosensitive and 6 were solely chemosensitive. Hence, the majority of cardiac vagal C-fibres are likely to be bimodal, responding to both cardiac filling pressure and serotonin 5HT(3) receptor stimulation. Our results emphasize the potential role of endogenous mediators in the afferent limb of cardiac reflexes.

The role of 5-HT on the cardiovascular and renal systems and the clinical potential of 5-HT modulation

The main peripheral sources of 5-hydroxytryptamine (5-HT) are as a neurotransmitter and local hormone in the gastrointestinal tract, and stored in circulating platelets and pulmonary neuroepithelial bodies. 5-HT has been shown to have many possible physiological and pathophysiological roles on the cardiovascular and renal systems. Thus, 5-HT may contribute to valvular heart disease, coronary artery disease, pulmonary hypertension, pulmonary embolism, pre-eclampsia, peripheral vascular disease and diabetic nephropathy. Consequently, modulators of the 5-HT system have diverse clinical potential. For instance, selective 5-HT subtype 3 receptor (5-HT(3)) antagonists may have potential in the treatment of the pain associated with myocardial infarction. MCI-9042 (sarpogrelate) or other 5-HT(2A) antagonists may have clinical potential for the treatment of vasospastic angina, ischaemic heart disease, reperfusion injury and hindlimb ischaemia. Several modulators of 5-HT (5-HT transporter inhibitors, 5-HT(1B) and (2B) antagonists) may have potential alone or in combination in the treatment of pulmonary hypertension. In hypertension, agonists at the 5-HT(7) and antagonists at the 5-HT(2B) may reduce blood pressure, and in diabetes, sarpogrelate may protect against nephropathy.

Quantitation of papillary muscle function with tissue and strain Doppler echocardiography measures papillary muscle contractile functions

It is well known that papillary muscle dysfunction may cause mitral regurgitation, however, there is not a standard technique to measure the papillary muscle function. The aim of this study is to investigate papillary muscle function by using tissue and strain rate Doppler echocardiography.

METHOD

A study group (SG) of 42 patients (12 females, 30 males, mean age: 53.8 +/- 10.9 years) with coronary artery disease who have segmental left ventricular dysfunction and mitral regurgitation, and as a control group (CG) 20 patients (6 females, 14 males, mean age 52.5 +/- 10.2 years) who have no coronary artery disease and mitral regurgitation were studied. A subgroup 20 patients (7 females, 13 males, mean age 42.5 +/- 7.5 years) who have rheumatic mitral regurgitation was included to the study. The patients who have left ventricular and mitral annular dilatation were not included into the study. Longitudinal wall motion of mid-inferior segment (one point) and posterior papillary muscle (two point) of the left ventricle was assessed by tissue and strain rate Doppler echocardiography from the apical two-chamber view. Systolic tissue velocity (Sm), strain rate (SR), and strain (S) were measured from the two points in all patients.

RESULTS

Comparing the one point values Sm, SR, and S were found less in SG than CG (respectively 4.2 +/- 1.4 vs 11.3 +/- 1.9 cm/sec, -1.0 +/- 0.4 vs -1.7 +/- 0.3 s-1, -13.5 +/- 5.0 vs -18.1 +/- 3.9%; P < 0.001 for all). Comparing the two point values Sm, SR and S were found less in SG than CG (respectively 2.8 +/- 1.2 vs 3.7 +/- 2.0 cm/sec, -0.8 +/- 0.4 vs -1.6 +/- 0.3 s-1, -9.7 +/- 4.6 vs -15.8 +/- 3.7%; P < 0.001 for all). Systolic mitral annulus, left ventricular systolic and diastolic dimensions were similar in two groups. Comparing the CG and subgroup, there were no significant differences with respect to Sm, SR, and S measured from the two points.

CONCLUSIONS

Papillary muscle function may be assessed quantitatively by using tissue and strain rate Doppler echocardiography. Tissue velocity, strain rate, and strain values were found decreased in dysfunctional papillary muscle.

Activated platelets contribute to stimulation of cardiac afferents during ischaemia in cats: role of 5-HT(3) receptors

Myocardial ischaemia activates blood platelets and cardiac sympathetic afferents, which mediate chest pain and cardiovascular reflex responses. We have demonstrated that activated platelets stimulate ischaemically sensitive cardiac sympathetic afferents. Platelets absorb and release 5-hydroxytryptamine (5-HT) when they are activated. In the present study we hypothesized that, by releasing 5-HT, activated platelets stimulate cardiac afferents during ischaemia through a 5-HT(3) receptor mechanism. Platelet-rich plasma (PRP) and platelet-poor plasma (PPP) were obtained from cats. Activation of platelets in PRP was induced by thrombin (5 units ml(-1)) or collagen (2 mg kg(-1)). Using high-performance liquid chromatography, we observed that the concentration of 5-HT was increased significantly in suspensions of platelets activated with thrombin (PRP+thrombin, 28 +/- 1.7 microM) or collagen (PRP+collagen, 27 +/- 2.5 microM) compared with suspensions of unactivated platelets (PRP+saline, 2.3 +/- 0.8 microM) and PPP. During myocardial ischaemia and reperfusion, tirofiban, a specific inhibitor of platelet glycoprotein (GP) IIb-IIIa receptors (100 microg kg(-1), I.V., followed by 5 microg kg(-1) min(-1)), significantly reduced the increase in the concentration of 5-HT in cardiac venous plasma from ischaemic region. Nerve activity of single-unit cardiac afferents was recorded from the left sympathetic chain (T2-T5) in anaesthetized cats. Eighty ischaemically sensitive and seven ischaemically insensitive cardiac afferents were identified. Tirofiban reduced the ischaemia-related increase in activity of seven cardiac sympathetic afferents by 50 %. Injection of 1.5 ml of PRP+collagen or PRP+thrombin into the left atrium (LA) increased activity of 16 cardiac afferents. Tropisetron (300 microg kg(-1), I.V.), a selective 5-HT(3) receptor antagonist, eliminated the afferent's responses to platelets activated with collagen or thrombin. Moreover, LA injection of 5-HT (20-40 microg kg(-1)) and PBG (100 microg kg(-1)), a 5-HT(3) receptor agonist, stimulated nine ischaemically sensitive cardiac sympathetic afferents, significantly increasing the activity of these afferents. However, injection of alpha-M-5-HT (100 microg kg(-1), LA), a 5-HT(2) receptor agonist, stimulated only two of the nine ischaemically sensitive cardiac afferents, and thus did not significantly alter impulse activity of this group of afferents. Both the 5-HT(1) (5-CT, 100 microg kg(-1), LA) and 5-HT(4) receptor agonists (SC53116, 100 microg kg(-1), LA) did not stimulate any of the nine afferents tested. Tropisetron (300 microg kg(-1), I.V.) also eliminated the response of seven ischaemically sensitive cardiac afferents to exogenous 5-HT and attenuated the ischaemia-related increase in activity of nine cardiac sympathetic afferents by 41 %. Conversely, LA injection of 5-HT (40 microg kg(-1)) did not stimulate any of seven ischaemically insensitive cardiac afferents, although this group of afferents consistently responded to bradykinin (3 microg, LA). These data indicate that during myocardial ischaemia the activated platelets stimulate cardiac sympathetic afferents, at least in part, through a 5-HT(3) receptor mechanism.

The role of serotonin in ischemic cellular damage and the infarct size-reducing effect of sarpogrelate, a 5-hydroxytryptamine-2 receptor blocker, in rabbit hearts

OBJECTIVE

We aimed to clarify the relation between sarpogrelate (SG), a 5-hydroxytryptamine (5-HT)-2 receptor blocker, and myocardial interstitial serotonin or infarct size during ischemia and reperfusion.

BACKGROUND

In cardiac tissues serotonin is rich in vascular platelets, mast cells, sympathetic nerve endings, and the receptors are present in platelets and cardiomyocytes.

METHODS

The myocardial interstitial serotonin levels were measured using a microdialysis technique during 30-min ischemia with and without SG in in vivo as well as isolated rabbit hearts. Other rabbits underwent 30 min of ischemia and 48 h of reperfusion, and the effect of SG on the infarct size was investigated in the absence and presence of a selective protein kinase C (PKC) inhibitor, chelerythrine (5 mg/kg, intravenously), or a mitochondrial adenosine triphosphate sensitive potassium (KATP) channel blocker, 5-hydroxydecanoate (5-HD) (5 mg/kg, intravenously). In another series, the effect of SG on PKC isoforms in cytosol and membrane fraction was assessed after a 20-min global ischemia in isolated rabbit hearts.

RESULTS

Interstitial serotonin levels were markedly increased during 30-min ischemia in in vivo and isolated hearts, and the increases were inhibited by SG in each. The infarct size was reduced by SG (27 +/- 2% vs. 40 +/- 3% of control). This effect was blocked by chelerythrine and 5-HD, respectively. Sarpogrelate further enhanced the ischemia-induced translocation of PKC-epsilon to the membrane fraction.

CONCLUSIONS

Sarpogrelate reduces the myocardial infarct size by inhibiting the serotonin release followed by enhancement of PKC-epsilon translocation and opening of the mitochondrial KATP channel in ischemic myocytes.