Local platelet activation causes vasoconstriction of large epicardial canine coronary arteries in vivo. Thromboxane A2 and serotonin are possible mediators

Imaging the time course, morphology, neuronal tissue compression, and resolution of cerebral microhemorrhages in mice using intravital two-photon microscopy: insights into arteriolar, capillary, and venular origin

Cerebral microhemorrhages (CMHs, microbleeds), a manifestation of age-related cerebral small vessel disease, contribute to the pathogenesis of cognitive decline and dementia in older adults. Histological studies have revealed that CMHs exhibit distinct morphologies, which may be attributed to differences in intravascular pressure and the size of the vessels of origin. Our study aimed to establish a direct relationship between the size/morphology of CMHs and the size/anatomy of the microvessel of origin. To achieve this goal, we adapted and optimized intravital two-photon microscopy-based imaging methods to monitor the development of CMHs in mice equipped with a chronic cranial window upon high-energy laser light-induced photodisruption of a targeted cortical arteriole, capillary, or venule. We assessed the time course of extravasation of fluorescently labeled blood and determined the morphology and size/volume of the induced CMHs. Our findings reveal striking similarities between the bleed morphologies observed in hypertension-induced CMHs in models of aging and those originating from different targeted vessels via multiphoton laser ablation. Arteriolar bleeds, which are larger (> 100 μm) and more widely dispersed, are distinguished from venular bleeds, which are smaller and exhibit a distinct diffuse morphology. Capillary bleeds are circular and smaller (< 10 μm) in size. Our study supports the concept that CMHs can occur at any location in the vascular tree, and that each type of vessel produces microbleeds with a distinct morphology. Development of CMHs resulted in immediate constriction of capillaries, likely due to pericyte activation and constriction of precapillary arterioles. Additionally, tissue displacement observed in association with arteriolar CMHs suggests that they can affect an area with a radius of ~ 50 μm to ~ 100 μm, creating an area at risk for ischemia. Longitudinal imaging of CMHs allowed us to visualize reactive astrocytosis and bleed resolution during a 30-day period. Our study provides new insights into the development and morphology of CMHs, highlighting the potential clinical implications of differentiating between the types of vessels involved in the pathogenesis of CMHs. This information may help in the development of targeted interventions aimed at reducing the risk of cerebral small vessel disease-related cognitive decline and dementia in older adults.

Hepatic transcript profiling in beef cattle: Effects of rumen-protected niacin supplementation

The objective of our study was to assess the effect of rumen-protected niacin supplementation on the transcriptome of liver tissue in growing Angus × Simmental steers and heifers through RNA-seq analysis. Consequently, we wanted to assess the known role of niacin in the physiological processes of vasodilation, detoxification, and immune function in beef hepatic tissue. Normal weaned calves (~8 months old) were provided either a control diet or a diet supplemented with rumen-protected niacin (6 g/hd/d) for a 30-day period, followed by a liver biopsy. We observed a significant list of changes at the transcriptome level due to rumen-protected niacin supplementation. Several metabolic pathways revealed potential positive effects to the animal's liver metabolism due to administration of rumen-protected niacin; for example, a decrease in lipolysis, apoptosis, inflammatory responses, atherosclerosis, oxidative stress, fibrosis, and vasodilation-related pathways. Therefore, results from our study showed that the liver transcriptional machinery switched several metabolic pathways to a condition that could potentially benefit the health status of animals supplemented with rumen-protected niacin. In conclusion, based on the results of our study, we can suggest the utilization of rumen-protected niacin supplementation as a nutritional strategy could improve the health status of growing beef cattle in different beef production stages, such as backgrounding operations or new arrivals to a feedlot.

Favorable Vasomotor Function after Drug-Coated Balloon-Only Angioplasty of De Novo Native Coronary Artery Lesions

Balloon-injured coronary segments are known to harbor abnormal vasomotion. We evaluated whether de novo coronary lesions treated using drug-coated balloon (DCB) are prone to vasospasm and how they respond to ergonovine and nitrate. Among 132 DCB angioplasty recipients followed, 89 patients underwent ergonovine provocation test at 6–9 months follow-up. Within-subject ergonovine- and nitrate-induced diameter changes were compared among three different sites: DCB-treated vs. angiographically normal vs. segment showing prominent vasoreactivity (spastic). No patient experienced clinically refractory vasospastic angina or symptom-driven revascularization during follow-up. Ergonovine induced vasospasm in seven patients; all were multifocal spasm either involving (n = 2) or rather sparing DCB-treated segments (n = 5). None showed focal spasm that exclusively involved DCB-treated lesions. Among 27 patients with vasospastic features, DCB-treated segments showed less vasoconstriction than spastic counterparts (p < 0.001). A total of 110 DCB-treated lesions were analyzed to assess vasomotor function. Vasomotor function, defined as a combined constrictor and dilator response, was comparable between DCB-treated and angiographically normal segments (p = 0.173), while significant differences were observed against spastic counterparts (p < 0.001). In our study, DCB-treated lesions were not particularly vulnerable to vasospasm and were found to have vasomotor function similar to angiographically normal segments, supporting safety of DCB-only strategy in treating de novo native coronary lesions.

Endothelial Dysfunction in Atherosclerotic Cardiovascular Diseases and Beyond: From Mechanism to Pharmacotherapies

The endothelium, a cellular monolayer lining the blood vessel wall, plays a critical role in maintaining multiorgan health and homeostasis. Endothelial functions in health include dynamic maintenance of vascular tone, angiogenesis, hemostasis, and the provision of an antioxidant, anti-inflammatory, and antithrombotic interface. Dysfunction of the vascular endothelium presents with impaired endothelium-dependent vasodilation, heightened oxidative stress, chronic inflammation, leukocyte adhesion and hyperpermeability, and endothelial cell senescence. Recent studies have implicated altered endothelial cell metabolism and endothelial-to-mesenchymal transition as new features of endothelial dysfunction. Endothelial dysfunction is regarded as a hallmark of many diverse human panvascular diseases, including atherosclerosis, hypertension, and diabetes. Endothelial dysfunction has also been implicated in severe coronavirus disease 2019. Many clinically used pharmacotherapies, ranging from traditional lipid-lowering drugs, antihypertensive drugs, and antidiabetic drugs to proprotein convertase subtilisin/kexin type 9 inhibitors and interleukin 1β monoclonal antibodies, counter endothelial dysfunction as part of their clinical benefits. The regulation of endothelial dysfunction by noncoding RNAs has provided novel insights into these newly described regulators of endothelial dysfunction, thus yielding potential new therapeutic approaches. Altogether, a better understanding of the versatile (dys)functions of endothelial cells will not only deepen our comprehension of human diseases but also accelerate effective therapeutic drug discovery. In this review, we provide a timely overview of the multiple layers of endothelial function, describe the consequences and mechanisms of endothelial dysfunction, and identify pathways to effective targeted therapies. SIGNIFICANCE STATEMENT: The endothelium was initially considered to be a semipermeable biomechanical barrier and gatekeeper of vascular health. In recent decades, a deepened understanding of the biological functions of the endothelium has led to its recognition as a ubiquitous tissue regulating vascular tone, cell behavior, innate immunity, cell-cell interactions, and cell metabolism in the vessel wall. Endothelial dysfunction is the hallmark of cardiovascular, metabolic, and emerging infectious diseases. Pharmacotherapies targeting endothelial dysfunction have potential for treatment of cardiovascular and many other diseases.

Changes in serum serotonin levels in patients with acute coronary syndrome and stable angina undergoing percutaneous coronary intervention

OBJECTIVE

Activated platelets release serotonin, causing platelet aggregation and vasoconstriction. Serotonin levels were investigated in patients with acute coronary syndrome (ACS) and chronic stable angina (CSA) treated with percutaneous coronary intervention (PCI).

METHODS

Consecutive patients undergoing PCI for either ACS or CSA were enrolled between July 2009 and April 2010. Patients were pre-treated with dual antiplatelet agents (aspirin and clopidogrel) before PCI. Serum serotonin levels, measured at baseline, pre- and post-PCI, and at 90 min, and 6, 12, 24 and 48 h following PCI, were compared between ACS and CSA groups.

RESULTS

Sixty-three patients with ACS and 60 with CSA were included. Overall baseline characteristics were similar between the two groups. Serotonin levels at post-PCI (55.2 ± 120.0 versus 20.1 ± 24.0) and at peak (regardless of timepoint; 94.0 ± 170.9 versus 38.8 ± 72.3) were significantly higher in the ACS versus CSA group. At 90 min and 6, 24 and 48 h post-PCI, serum serotonin was numerically, but not significantly, higher in patients with ACS. Serotonin levels fluctuated in both groups, showing an initial rise and fall, rebound at 24 h and drop at 48 h post-PCI.

CONCLUSIONS

In patients undergoing PCI, serum serotonin was more elevated in patients with ACS than those with CSA, suggesting the need for more potent and sustained platelet inhibition, particularly in patients with ACS.

Serotonin uptake via plasma membrane monoamine transporter during myocardial ischemia-reperfusion in the rat heart in vivo

Serotonin (5-HT) accumulates in the heart during myocardial ischemia and induces deleterious effects on the cardiomyocytes through receptor-dependent and monoamine oxidase-dependent pathways. We aimed to clarify the involvement of extra-neuronal monoamine transporters in the clearance of 5-HT during ischemia and reperfusion in the heart. Using a microdialysis technique in the anesthetized Wistar rat heart, we monitored myocardial interstitial 5-HT and 5-hydroxyindole acetic acid (5-HIAA) concentration by means of electro-chemical detection coupled with high-performance liquid chromatography (HPLC-ECD). Effects of inhibitors of the plasma membrane monoamine transporter (PMAT) and the organic cation transporter 3 (OCT3) (decynium-22 and corticosterone) on the 5-HT and 5-HIAA concentrations during baseline, coronary occlusion, and reperfusion were investigated. Basal dialysate 5-HT concentration were increased by local administration of decynium-22, but not by corticosterone. Addition of fluoxetine, a serotonin transporter (SERT) inhibitor further increased the 5-HT concentration upon during administration of decynium-22. Decynium-22 elevated the background level of 5-HT during coronary occlusion and maintained 5-HT concentration at a high level during reperfusion. Production of 5-HIAA in the early reperfusion was significantly suppressed by decynium-22. These results indicate that PMAT and SERT independently regulate basal level of interstitial 5-HT, and PMAT plays a more important role in the clearance of 5-HT during reperfusion. These data suggest the involvement of PMAT in the monoamine oxidase-dependent deleterious pathway in the heart.

Mechanisms of electrical vasoconstriction

BACKGROUND

Electrical vasoconstriction is a promising approach to control blood pressure or restrict bleeding in non-compressible wounds. We explore the neural and non-neural pathways of electrical vasoconstriction in-vivo.

METHODS

Charge-balanced, asymmetric pulses were delivered through a pair of metal disc electrodes. Vasoconstriction was assessed by measuring the diameter of rat saphenous vessels stimulated with low-voltage (20 V, 1 ms) and high-voltage (150 V, 10 μs) stimuli at 10 Hz for 5 min. Activation pathways were explored by topical application of a specific neural agonist (phenylephrine, alpha-1 receptor), a non-specific agonist (KCl) and neural inhibitors (phenoxybenzamine, 25 mg/ml; guanethidine, 1 mg/ml). Acute tissue damage was assessed with a membrane permeability (live-dead) fluorescent assay. The Joule heating in tissue was estimated using COMSOL Multiphysics modeling.

RESULTS

During stimulation, arteries constricted to 41 ± 8% and 37 ± 6% of their pre-stimulus diameter with low- and high-voltage stimuli, while veins constricted to 80 ± 18% and 40 ± 11%, respectively. In arteries, despite similar extent of constriction, the recovery time was very different: about 30 s for low-voltage and 10 min for high-voltage stimuli. Neural inhibitors significantly reduced low-voltage arterial constriction, but did not affect high-voltage arterial or venous constriction, indicating that high-voltage stimuli activate non-neural vasoconstriction pathways. Adrenergic pathways predominantly controlled low-voltage arterial but not venous constriction, which may involve a purinergic pathway. Viability staining confirmed that stimuli were below the electroporation threshold. Modeling indicates that heating of the blood vessels during stimulation (< 0.2 °C) is too low to cause vasoconstriction.

CONCLUSIONS

We demonstrate that low-voltage stimuli induce reversible vasoconstriction through neural pathways, while high-voltage stimuli activate non-neural pathways, likely in addition to neural stimulation. Different stimuli providing precise control over the extent of arterial and venous constriction as well as relaxation rate could be used to control bleeding, perfusion or blood pressure.

Activation of the Serotonin Pathway is Associated with Poor Outcome in COPD Exacerbation: Results of a Long-Term Cohort Study

BACKGROUND/INTRODUCTION

Indoleamine 2,3-dioxygenase (IDO) metabolizes tryptophan to kynurenine. An increase of its activity is associated with severity in patients with pneumonia. In chronic obstructive pulmonary disease (COPD) patients, an elevation of serotonin has been reported. Experimental models showed that cigarette smoke inhibits monoamine oxidase (MAO) leading to higher levels of serotonin. We investigated the prognostic ability of tryptophan, serotonin, kynurenine, IDO, and tryptophan hydroxylase (TPH) to predict short- and long-term outcomes in patients with a COPD exacerbation.

METHODS

We measured tryptophan, serotonin, and kynurenine on admission plasma samples in patients with a COPD exacerbation from a previous trial by liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS). IDO and TPH were calculated as ratios of kynurenine over tryptophan, and serotonin over tryptophan, respectively. We studied their association with parameters measured in clinical routine at emergency department admission representing inflammation (C-reactive protein [CRP]), infection (procalcitonin [PCT]), oxygenation (SpO₂), as well as patients' clinical outcome, confirmed by structured phone interviews.

RESULTS

Mortality in the 149 included patients was 53.7% within six years of follow-up. While IDO activity showed strong positive correlations, tryptophan was negatively correlated with CRP and PCT. For 30-day adverse outcome defined as death and/or intensive care unit (ICU) admission, a multivariate regression analysis adjusted for age and comorbidities found strong associations for IDO activity (adjusted odds ratios of 31.4 (95%CI 1.1-857), p = 0.041) and TPH (adjusted odds ratios 27.0 (95%CI 2.2-327), p = 0.010). TPH also showed a significant association with mortality at 18 months, (hazard ratio 2.61 (95%CI 1.2-5.8), p = 0.020).

CONCLUSION

In hospitalized patients with a COPD exacerbation, higher IDO and TPH activities independently predicted adverse short-term outcomes and TPH levels were also predictive of 18-month mortality. Whether therapeutic modulation of the serotonin pathway has positive effects on outcome needs further investigation.

Regulation of Coronary Blood Flow

The heart is uniquely responsible for providing its own blood supply through the coronary circulation. Regulation of coronary blood flow is quite complex and, after over 100 years of dedicated research, is understood to be dictated through multiple mechanisms that include extravascular compressive forces (tissue pressure), coronary perfusion pressure, myogenic, local metabolic, endothelial as well as neural and hormonal influences. While each of these determinants can have profound influence over myocardial perfusion, largely through effects on end-effector ion channels, these mechanisms collectively modulate coronary vascular resistance and act to ensure that the myocardial requirements for oxygen and substrates are adequately provided by the coronary circulation. The purpose of this series of Comprehensive Physiology is to highlight current knowledge regarding the physiologic regulation of coronary blood flow, with emphasis on functional anatomy and the interplay between the physical and biological determinants of myocardial oxygen delivery. © 2017 American Physiological Society. Compr Physiol 7:321-382, 2017.

Myocardial interstitial levels of serotonin and its major metabolite 5-hydroxyindole acetic acid during ischemia-reperfusion

The aim of this study was to examine the accumulation of serotonin (5-HT) and degradation of 5-HT taken up into cells in the ischemic region during myocardial ischemia-reperfusion. Using microdialysis technique in anesthetized rats, we monitored myocardial interstitial levels of 5-HT and its metabolite produced by monoamine oxidase (MAO), 5-hydroxyindole acetic acid (5-HIAA), during 30-min coronary occlusion followed by 45-min reperfusion, and investigated the effects of local administration of the MAO inhibitor pargyline and the 5-HT uptake inhibitor fluoxetine. In the vehicle group, the dialysate 5-HT concentration increased from 1.3 ± 0.2 nM at baseline to 29.6 ± 2.8 nM at 22.5-30 min of occlusion, but the dialysate 5-HIAA concentration did not change from baseline (9.9 ± 1.1 nM). Upon reperfusion, the dialysate 5-HT concentration increased further to a peak (34.2 ± 4.2 nM) at 0-7.5 min and then declined. The dialysate 5-HIAA concentration increased to 31.9 ± 5.2 nM at 7.5-15 min of reperfusion and maintained this high level until 45 min. Pargyline markedly suppressed the increase in dialysate 5-HIAA concentration after reperfusion and increased the averaged dialysate 5-HT concentration during the reperfusion period. Fluoxetine suppressed the increase in dialysate 5-HT concentration during occlusion but did not change dialysate 5-HT or 5-HIAA concentration after reperfusion. During ischemia, 5-HT secreted from ischemic tissues accumulates but 5-HT degradation by MAO is suppressed. After reperfusion, degradation of 5-HT taken up into cells is enhanced and contributes to the clearance of accumulated 5-HT. This degradation following cellular uptake is dependent on MAO activity but not the fluoxetine-sensitive uptake transporter.

NEW & NOTEWORTHY

By monitoring myocardial interstitial levels of 5-HT and its metabolite, 5-hydroxyindole acetic acid, we investigated 5-HT kinetics during myocardial ischemia-reperfusion. 5-HT accumulates but 5-HT degradation is suppressed during ischemia. After reperfusion, 5-HT degradation is enhanced and this degradation is dependent on monoamine oxidase activity but not fluoxetine-sensitive uptake transporter.

Partially Defective Store Operated Calcium Entry and Hem(ITAM) Signaling in Platelets of Serotonin Transporter Deficient Mice

BACKGROUND

Serotonin (5-hydroxytryptamin, 5-HT) is an indolamine platelet agonist, biochemically derived from tryptophan. 5-HT is secreted from the enterochromaffin cells into the gastrointestinal tract and blood. Blood 5-HT has been proposed to regulate hemostasis by acting as a vasoconstrictor and by triggering platelet signaling through 5-HT receptor 2A (5HTR2A). Although platelets do not synthetize 5-HT, they take 5-HT up from the blood and store it in their dense granules which are secreted upon platelet activation.

OBJECTIVE

To identify the molecular composite of the 5-HT uptake system in platelets and elucidate the role of platelet released 5-HT in thrombosis and ischemic stroke.

METHODS

5-HT transporter knockout mice (5Htt-/-) were analyzed in different in vitro and in vivo assays and in a model of ischemic stroke.

RESULTS

In 5Htt-/- platelets, 5-HT uptake from the blood was completely abolished and agonist-induced Ca2+ influx through store operated Ca2+ entry (SOCE), integrin activation, degranulation and aggregation responses to glycoprotein VI (GPVI) and C-type lectin-like receptor 2 (CLEC-2) were reduced. These observed in vitro defects in 5Htt-/- platelets could be normalized by the addition of exogenous 5-HT. Moreover, reduced 5-HT levels in the plasma, an increased bleeding time and the formation of unstable thrombi were observed ex vivo under flow and in vivo in the abdominal aorta and carotid artery of 5Htt-/- mice. Surprisingly, in the transient middle cerebral artery occlusion (tMCAO) model of ischemic stroke 5Htt-/- mice showed nearly normal infarct volume and the neurological outcome was comparable to control mice.

CONCLUSION

Although secreted platelet 5-HT does not appear to play a crucial role in the development of reperfusion injury after stroke, it is essential to amplify the second phase of platelet activation through SOCE and plays an important role in thrombus stabilization.

Formation of blood clot on biomaterial implants influences bone healing

The first step in bone healing is forming a blood clot at injured bones. During bone implantation, biomaterials unavoidably come into direct contact with blood, leading to a blood clot formation on its surface prior to bone regeneration. Despite both situations being similar in forming a blood clot at the defect site, most research in bone tissue engineering virtually ignores the important role of a blood clot in supporting healing. Dental implantology has long demonstrated that the fibrin structure and cellular content of a peri-implant clot can greatly affect osteoconduction and de novo bone formation on implant surfaces. This article reviews the formation of a blood clot during bone healing in relation to the use of platelet-rich plasma (PRP) gels. It is implicated that PRP gels are dramatically altered from a normal clot in healing, resulting in conflicting effect on bone regeneration. These results indicate that the effect of clots on bone regeneration depends on how the clots are formed. Factors that influence blood clot structure and properties in relation to bone healing are also highlighted. Such knowledge is essential for developing strategies to optimally control blood clot formation, which ultimately alter the healing microenvironment of bone. Of particular interest are modification of surface chemistry of biomaterials, which displays functional groups at varied composition for the purpose of tailoring blood coagulation activation, resultant clot fibrin architecture, rigidity, susceptibility to lysis, and growth factor release. This opens new scope of in situ blood clot modification as a promising approach in accelerating and controlling bone regeneration.

Contribution of serotonin uptake and degradation to myocardial interstitial serotonin levels during ischaemia-reperfusion in rabbits

AIM

Although deleterious effects of serotonin (5-HT) have been demonstrated during myocardial ischaemia-reperfusion, little information is available on myocardial interstitial 5-HT kinetics. This study evaluated the contribution of 5-HT reuptake and degradation to myocardial interstitial 5-HT levels during ischaemia-reperfusion.

METHODS

Using microdialysis technique in anaesthetized rabbits, we monitored myocardial interstitial 5-HT levels in the ischaemic region during ischaemia (30 min) followed by reperfusion (60 min) and investigated the effects of local infusion of fluoxetine, a 5-HT uptake inhibitor, and/or pargyline, a monoamine oxidase inhibitor.

RESULTS

In vehicle control, dialysate 5-HT concentration increased gradually from 16 ± 3 at baseline to 85 ± 18 nM during 20-30 min of ischaemia. Dialysate 5-HT concentration further increased to 236 ± 47 nM at 0-10 min of reperfusion and then began to decline. Averaged 5-HT concentration was 61 ± 11 during ischaemia and 113 ± 13 nM during reperfusion. Fluoxetine elevated dialysate 5-HT level at baseline and at 10-30 min of reperfusion; it increased averaged dialysate 5-HT concentration by approx. 304% during reperfusion compared to control. Pargyline elevated averaged dialysate 5-HT concentration during ischaemia by approx. 243% and that during reperfusion by approx. 250% compared to control. The changes in dialysate 5-HT concentration by fluoxetine + pargyline were similar to those of fluoxetine alone.

CONCLUSION

The 5-HT reuptake function plays an important role in the clearance of myocardial interstitial 5-HT during reperfusion. When 5-HT reuptake function is intact, degradation of 5-HT by monoamine oxidase contributes to reduce myocardial interstitial 5-HT level throughout ischaemia-reperfusion.

Secretome of apoptotic peripheral blood cells (APOSEC) attenuates microvascular obstruction in a porcine closed chest reperfused acute myocardial infarction model: role of platelet aggregation and vasodilation

Although epicardial blood flow can be restored by an early intervention in most cases, a lack of adequate reperfusion at the microvascular level is often a limiting prognostic factor of acute myocardial infarction (AMI). Our group has recently found that paracrine factors secreted from apoptotic peripheral blood mononuclear cells (APOSEC) attenuate the extent of myocardial injury. The aim of this study was to determine the influence of APOSEC on microvascular obstruction (MVO) in a porcine AMI model. A single dose of APOSEC was intravenously injected in a closed chest reperfused infarction model. MVO was determined by magnetic resonance imaging and cardiac catheterization. Role of platelet function and vasodilation were monitored by means of ELISA, flow cytometry, aggregometry, western blot and myographic experiments in vitro and in vivo. Treatment of AMI with APOSEC resulted in a significant reduction of MVO. Platelet activation markers were reduced in plasma samples obtained during AMI, suggesting an anti-aggregatory capacity of APOSEC. This finding was confirmed by in vitro tests showing that activation and aggregation of both porcine and human platelets were significantly impaired by co-incubation with APOSEC, paralleled by vasodilator-stimulated phosphoprotein (VASP)-mediated inhibition of platelets. In addition, APOSEC evidenced a significant vasodilatory capacity on coronary arteries via p-eNOS and iNOS activation. Our data give first evidence that APOSEC reduces the extent of MVO during AMI, and suggest that modulation of platelet activation and vasodilation in the initial phase after myocardial infarction contributes to the improved long-term outcome in APOSEC treated animals.

Serotonin antagonism improves platelet inhibition in clopidogrel low-responders after coronary stent placement: an in vitro pilot study

Increased residual platelet reactivity remains a burden for coronary artery disease (CAD) patients who received a coronary stent and do not respond sufficiently to treatment with acetylsalicylic acid and clopidogrel. We hypothesized that serotonin antagonism reduces high on-treatment platelet reactivity. Whole blood impedance aggregometry was performed with arachidonic acid (AA, 0.5 mM) and adenosine diphosphate (ADP, 6.5 µM) in addition to different concentrations of serotonin (1-100 µM) in whole blood from 42 CAD patients after coronary stent placement and 10 healthy subjects. Serotonin increased aggregation dose-dependently in CAD patients who responded to clopidogrel treatment: After activation with ADP, aggregation increased from 33.7 ± 1.3% to 40.9 ± 2.0% in the presence of 50 µM serotonin (p<0.05) and to 48.2 ± 2.0% with 100 µM serotonin (p<0.001). The platelet serotonin receptor antagonist ketanserin decreased ADP-induced aggregation significantly in clopidogrel low-responders (from 59.9 ± 3.1% to 37.4 ± 3.5, p<0.01), but not in clopidogrel responders. These results were confirmed with light transmission aggregometry in platelet-rich plasma in a subset of patients. Serotonin hence increased residual platelet reactivity in patients who respond to clopidogrel after coronary stent placement. In clopidogrel low-responders, serotonin receptor antagonism improved platelet inhibition, almost reaching responder levels. This may justify further investigation of triple antiplatelet therapy with anti-serotonergic agents.

Decreased serotonin content and reduced agonist-induced aggregation in platelets of patients chronically medicated with SSRI drugs

BACKGROUND

Chronic treatment with selective serotonin reuptake inhibitors (SSRIs) reduces the risk and severity of cardiovascular diseases. SSRIs block the serotonin transporter, thereby inhibiting serotonin (5-HT) uptake into presynaptic neurons as well as into platelets where 5-HT is stored in dense granules. When 5-HT is released in response to agonists it enhances platelet aggregation induced by injury-related signals. Chronic administration of SSRIs may thus reduce platelet aggregability secondary to depletion of platelets' serotonin stores.

METHODS

The study included ten DSM-IV-TR major depression (MDD) and four obsessive compulsive disorder (OCD) patients and fourteen healthy untreated age- and sex-matched controls. The patients were chronically medicated (6-108 months) with various SSRIs. Platelet serotonin content was assessed in fresh samples of platelet rich plasma (PRP) using radioimmunoassay. ADP, collagen, arachidonic acid and epinephrine were used as inducers of platelet aggregation measured in PRP by turbometric method in a microplate reader.

RESULTS

Lower platelet serotonin content (66%; p<0.05) and lower ADP, collagen or epinephrine-induced platelet aggregation (10-52%; p<0.05) were detected in PRP of SSRI-medicated patients, while no such effect was obtained with arachidonic acid.

LIMITATIONS

The small sample size and the co-treatment with non-SSRI drugs such as benzodiazepines.

CONCLUSION

Patients chronically medicated with SSRIs exhibit lower platelet 5-HT content and reduced platelet aggregation induced by ADP, collagen and epinephrine, but not by arachidonic acid. Our observations may explain the increased bleeding risk associated with chronic SSRI treatment as well as the reported beneficial effect of SSRIs in prevention of recurrent myocardial infarction.

In vivo models for the evaluation of antithrombotics and thrombolytics

The development and application of animal models of thrombosis have played a crucial role in the discovery and validation of novel drug targets and the selection of new agents for clinical evaluation, and have informed dosing and safety information for clinical trials. These models also provide valuable information about the mechanisms of action/interaction of new antithrombotic agents. Small and large animal models of thrombosis and their role in the discovery and development of novel agents are described. Methods and major issues regarding the use of animal models of thrombosis, such as positive controls, appropriate pharmacodynamic markers of activity, safety evaluation, species specificity, and pharmacokinetics, are highlighted. Finally, the use of genetic models of thrombosis/hemostasis and how these models have aided in the development of therapies that are presently being evaluated clinically are presented.

Relationship of admission hematological indexes with myocardial reperfusion abnormalities in acute ST segment elevation myocardial infarction patients treated with primary percutaneous coronary interventions

BACKGROUND

Elevated values of mean platelet volume (MPV) and elevated white blood cell (WBC) count are predictors of an unfavourable outcome among survivors of ST segment elevation myocardial infarction (STEMI). However, their relationship with reperfusion abnormalities is less clear.

OBJECTIVE

To evaluate the value of admission MPV and WBC count in predicting impaired reperfusion in patients with acute STEMI who are treated with primary percutaneous coronary intervention (PCI).

METHODS

Blood samples were obtained on admission from 368 STEMI patients who underwent successful PCI. According to the 60th minute ST segment resolution ratio, patients were divided into impaired reperfusion and reperfusion groups.

RESULTS

Impaired reperfusion was detected in 40% of study patients. Patients in the impaired reperfusion group had a higher admission MPV (9.8+/-1.3 fL versus 8.6+/-1.0 fL; P<0.001) and a higher WBC count (14.4+/-5.5 x 10(9)/L versus 12.1+/-3.8 x 10(9)/L; P<0.001) compared with the patients in the reperfusion group. In regression analysis, MPV (OR 2.21, 95% CI 1.69 to 2.91; P<0.001) and WBC count (OR 1.08, 95% CI 1.02 to 1.15; P=0.01) were found to be independently associated with impaired reperfusion. The best cut-off value of MPV for predicting impaired reperfusion was determined to be 9.05 fL, with a sensitivity of 74% and a specificity of 73%.

CONCLUSIONS

The results indicate that leukocytes and platelets have a role in the mediation of reperfusion injury. In patients with STEMI who are undergoing PCI, admission MPV may be valuable in discriminating a higher-risk patient subgroup and thus, may help in deciding the need for adjunctive therapy to improve the outcome.

Salutary effects of aspirin in coronary artery disease are not limited to its platelet inhibitory effects

Aspirin is widely used in the treatment and prevention of coronary artery disease (CAD). However, other platelet inhibitory agents, which inhibit platelet activation, have not been found to be effective or as effective as aspirin. The discrepancy between the efficacy of these compounds and aspirin suggests that the therapeutic efficacy of aspirin may not be limited to its platelet inhibitory effect. In this review, the basis for a unique place for aspirin in the therapy of patients with CAD is discussed. The author believes that the nonplatelet-mediated effects of aspirin could be more important than the platelet inhibitory effect, or at least may complement the platelet inhibitory effects of aspirin in patients with acute myocardial ischemia and in others undergoing intracoronary procedures.

Correlates of bundle-branch block in patients undergoing primary angioplasty for acute myocardial infarction

BACKGROUND

Early reperfusion therapy has reduced the infarct size and mortality rate in patients with acute myocardial infarction (AMI). The occurrence of bundle-branch block in AMI is related to the amount of myocardial damage and the insult to the conduction system.

HYPOTHESIS

To evaluate the clinical and angiographic factors related to the occurrence of bundle-branch block (BBB) in patients with primary percutaneous transluminal coronary angioplasty (PTCA), we investigated consecutive series of patients with their first Q-wave AMI and successful PTCA.

METHODS

Coronary angiogram at the time of admission, electrocardiogram, and echocardiogram were evaluated in 279 patients with their first Q-wave AMI and successful PTCA.

RESULTS

Bundle-branch block was detected in 26 patients (9%); 16 patients had transient and 10 patients had persistent block, while 16 patients had bifascicular block and 10 patients had right BBB. The patients with BBB had a significantly larger number of left ventricular asynergic segments, higher incidence of total occlusion of infarct-related artery, angiographic no reflow, and pericardial rub than those without BBB. When the multivariate analysis was performed using five clinical markers of infarct severity, angiographic no reflow (F = 20.2, p < 0.001) and total occlusion of infarct-re-lated artery (F = 4.2, p = 0.04) were found to be the significant variables related to BBB.

CONCLUSIONS

Despite successful primary PTCA, absence of antegrade flow in the infarct-related artery at the onset of AMI and/or angiographic no reflow resulted in more severe transmural myocardial damage and, hence, the occurrence of BBB.

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.

Platelet deposition in remote cardiac regions after coronary occlusion

BACKGROUND

Activated platelets might contribute to endothelial dysfunction in non-ischaemic territories during acute myocardial infarction. We assessed platelet deposition, coronary flow reserve and contractile function in remote cardiac regions after transient coronary occlusion and their association with systemic platelet activation.

MATERIALS AND METHODS

In 10 pigs (series A) subjected to 48-min occlusion of the left anterior descending coronary artery (LAD), 99mTc-platelet content in the right coronary artery (RCA) and its dependent myocardium was counted after reflow. In 10 pigs (series B) receiving the same occlusion of the RCA, the hyperaemic response at the LAD and systolic shortening in LAD-dependent myocardium were monitored after reperfusion. P-selectin expression on circulating platelets was assessed in both series by flow cytometry.

RESULTS

In series A, platelet counts in the RCA and non-ischaemic myocardium were correlated with platelet content, polymorphonuclear leukocyte infiltration and infarct size in the reperfused zone, as well as with the percentage of P-selectin-positive platelets after reflow. In series B, a transient reduction in peak hyperaemic response in the LAD and sustained contractile dysfunction in non-ischemic myocardium were observed after releasing the RCA occlusion, these changes being also correlated with platelet activation status.

CONCLUSIONS

Ischaemic injury triggers macro- and microvascular platelet deposition and causes an impairment in coronary flow reserve and contractile function in distant regions of the heart, which are related to activation of circulating platelets.

Hemodynamic factors and atheromatic plaque rupture in the coronary arteries: from vulnerable plaque to vulnerable coronary segment

Coronary plaque disruption with superimposed thrombosis is the underlying pathology in the acute coronary syndromes and sudden death. Coronary plaques are constantly stressed by a variety of mechanical and hemodynamic forces that may precipitate or 'trigger' disruption of vulnerable or, at extreme conditions, even stable plaques. This paper reviews the exciting new evidence on the hemodynamic factors that may play a role in this process and provides the rationale for the introduction of the concept of the vulnerable coronary segment in the study of acute coronary syndromes.

Frequency of slow coronary flow following successful stent implantation and effect of Nitroprusside

Nitroprusside (NTP) is used for the treatment of slow coronary flow (SCF) after coronary interventions. The wide variation in dosage, route, and timing of its administration in the reported studies prevents an objective assessment of its efficacy. We report the incidence and response to a standardized NTP protocol of SCF after successful stent implantation. Selective intracoronary administration of incremental doses (initial bolus of 80 microg incremented by 40 microg) of NPT was assessed in 21 patients who developed SCF in a series of 2,212 consecutive patients who underwent successful stent placement from January to October 2005. SCF was observed only in patients treated for acute myocardial infarction (AMI; 11.5%, 12 of 105) or saphenous vein graft (SVG) stenosis (8.2%, 9 of 109). An intracoronary bolus of nitroglycerin did not restore normal Thrombolysis In Myocardial Infarction (TIMI) flow in any patient. The first 80-microg dose of NTP restored normal TIMI flow in 58% of patients (7 of 12) with AMI and in 44% of patients (4 of 9)with SVG stenosis. The maximal dose (120/160 microg) restored normal TIMI flow in all remaining patients with AMI but in only 1 additional patient with SVG stenosis. At the end of the procedure, the percent decrease in corrected TIMI frame count was significantly larger in patients with AMI (-44+/-10%) than in those with SVG stenosis (-24+/-16%, p=0.02). In a large consecutive series of successful stent procedures, SCF was found only in patients with ST-elevation AMI (11.5%) or with a stenosed SVG (8.2%). In conclusion, the standardized protocol of intracoronary NTP administration succeeded in normalizing SCF in all patients with AMI but in only 5 of 9 patients with SVG stenosis. This latter subgroup requires other therapeutic strategies.

Honokiol up-regulates prostacyclin synthease protein expression and inhibits endothelial cell apoptosis

Honokiol is a bioactive compound extracted from the Chinese medicinal herb Magnolia officinalis. We recently demonstrated that honokiol inhibited arterial thrombosis through stimulation of prostacyclin (PGI2) generation and endothelial cell protection. The current study is designed to investigate its mechanism of stimulation of PGI2 generation and cell protection. 6-keto-PGF1alpha, the stable metabolite of PGI2, in the media of rat aortic endothelial cells was measured with radioimmunoassay kits. Indomethacin, an inhibitor of cyclooxygenase (COX) and tranylcypromine, a prostacyclin synthease inhibitor were used to ascertain the target enzyme affected by honokiol. Prostacyclin synthease protein levels in endothelial cells were determined by Western blot analysis using an anti-PGI2 synthease rabbit polyclonal antibody. Flow cytometry was used to quantify the apoptotic cells and spectrophotometry was used to test the caspase-3 activity. Honokiol (0.376-37.6 microM) increased the level of 6-keto-PGF1alpha in the media of normal endothelial cells. It counteracted the inhibitory effect of tranylcypromine on the PGI2 generation, but did not influence the effect of indomethacin; evidently, honokiol up-regulated the expression of prostacyclin synthease in the endothelial cells. These effects showed perfect concentration-dependent behavior. In addition, at lower concentration (0.376-3.76 microM), honokiol significantly decreased the percentage of apoptotic endothelial cells induced by oxidized low-density lipoprotein (ox-LDL) and significantly lowered the activity of caspase-3 stimulated by ox-LDL. A high dose of honokiol (37.6 microM), however, failed to influence either of them. In conclusion, honokiol augments PGI2 generation in normal endothelial cells; its effect on PGI2 generation attributes to up-regulation of prostacyclin synthease expression; its cell protection may be correlated with its inhibition on apoptosis of endothelial cells. These findings have partly revealed the molecular mechanism of honokiol on inhibiting arterial thrombosis.

Relationship between platelet monoamine oxidase-B (MAO-B) activity and mercury exposure in fish consumers from the Lake St. Pierre region of Que., Canada

Mercury (Hg) is a widespread neurotoxic compound that bio-accumulates in fish and marine mammals. Monoamine oxidase (MAO; EC 1.4.3.4) regulates biogenic amine concentration in the brain and peripheral tissue and has been shown to be a molecular target of Hg compounds in animal models. Blood platelet monoamine oxidase-B (MAO-B) activity may reflect MAO function in the central nervous tissue. Therefore, the objective of this study was to evaluate the relationship between platelet MAO-B and Hg exposure in fish-eating adults (n=127) living along the St. Lawrence River (Lake St. Pierre, Que., Canada). Hg concentrations were determined in blood and hair samples. A significant negative association was observed between platelet MAO-B activity and blood-Hg (r=-0.193, p=0.029) but not with hair-Hg levels (r=-0.125, p=0.169). Multiple linear regression analysis demonstrated that blood-Hg (beta=-4.6, p=0.011) and heavy smoking (beta=-8.5, p=0.001) were associated with reduced platelet MAO activity in the total population. In addition, this reduction in MAO-B activity appeared to be associated with blood-Hg concentrations above 3.4 microg/L (75th percentile). Possible gender related differences were also observed and are discussed. Our results suggest that MAO-B activity in blood platelets may be a useful tool to assess biochemical effects of Hg exposure in human populations. These changes in platelet MAO-B may reflect enzymatic changes in nervous tissue and should be further investigated as a surrogate marker of neurotoxicity.

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.

Beneficial effect of hydroxyfasudil, a specific Rho-kinase inhibitor, on ischemia/reperfusion injury in canine coronary microcirculation in vivo

OBJECTIVES

We examined whether hydroxyfasudil, a specific Rho-kinase inhibitor, exerts cardioprotective effect on coronary ischemia/reperfusion (I/R) injury and, if so, whether nitric oxide (NO) is involved.

BACKGROUND

Recent studies have demonstrated that Rho-kinase is substantially involved in the pathogenesis of cardiovascular diseases; however, it remains to be examined whether it is also involved in ischemia/reperfusion (I/R) injury.

METHODS

Canine subepicardial small arteries (SA, >or=100 microm) and arterioles (A, <100 microm) were observed by a charge-coupled device intravital microscope during I/R. Coronary vascular responses to endothelium-dependent (acetylcholine, intracoronary [IC]) and -independent (papaverine, IC) vasodilators were examined after I/R under the following four conditions: control (n = 7), NO synthase inhibitor alone (N(G)-monomethl-L-arginine [L-NMMA], IC, n = 4), hydroxyfasudil alone (IC, n = 7), and hydroxyfasudil plus L-NMMA (n = 7).

RESULTS

Hydroxyfasudil significantly attenuated serotonin (IC)-induced vasoconstriction of SA (-7 +/- 1% vs. 2 +/- 1%, p < 0.01). Coronary I/R significantly impaired coronary vasodilation to acetylcholine after I/R (SA, p < 0.05; and A, p < 0.01 vs. before I/R) and L-NMMA further reduced the vasodilation, whereas hydroxyfasudil completely preserved the responses. The vasoconstriction by L-NMMA after I/R was significantly improved by hydroxyfasudil in both-sized arteries (both p < 0.01). Expression of endothelial nitric oxide synthase (eNOS) protein in the ischemic endocardium of left anterior descending coronary artery area (as determined by Western blotting) significantly decreased (79 +/- 4%) compared with the nonischemic endocardium of LCX area (100 +/- 7%), which was improved by hydroxyfasudil (105 +/- 6%, p < 0.01). Hydroxyfasudil significantly reduced myocardial infarct size, and hydroxyfasudil with L-NMMA also reduced the infarct size compared with L-NMMA alone.

CONCLUSIONS

Hydroxyfasudil exerts cardioprotective effects on coronary I/R injury in vivo, in which NO-mediated mechanism may be involved through preservation of eNOS expression.

Mental and physical distress is modulated by a polymorphism in the 5-HT transporter gene interacting with social stressors and chronic disease burden

Previous studies have yielded conflicting results as to the putative role of the functional polymorphism of the promoter region of the serotonin transporter gene (SLC6A4) in the etiology of anxiety-related traits and depressive disorders. Recently, a significant gene-environment interaction was found between life stressors, the short allele of the SLC6A4 polymorphism and depression. The aim of the present study was to investigate if such a gene-environment interaction could be replicated within a different population with a different risk structure. A total of 1005 subjects from a general population sample (Study of Health in Pomerania) were genotyped. Mental and physical distress were assessed on 38 items of the modified complaint scale (BL-38). The interaction between the SLC6A4 genotype, social stressors and chronic diseases with regard to the BL-38 score was evaluated by ANOVA. There was no independent association of genotype with mental and physical distress. However, significant interactions between genotype, unemployment and chronic diseases (F = 6.6; df = 3, 671; P < 0.001) were found in females but not in males. The genotype explained 2% of the total variance of the BL-38 score and 9.1% of the explained variance. The results partly confirm previous findings of a significant gene-environment interaction of the short allele, indicating a higher mental vulnerability to social stressors and chronic diseases. The relevance of this finding is sustained by the fact that the sample characteristics and the risk structure were highly different from previous studies.

Amplification of sumatriptan-induced contraction in rabbit saphenous vein but not in basilar artery

The modulation of serotonin (5-HT(1B/1D)) receptor-induced vascular contractility by histamine and U-46619 was compared in the rabbit basilar artery and saphenous vein. In the saphenous vein, histamine (5 x 10(-7) M) significantly increased the potency (from pEC(50) of 6.0 to 6.8) and efficacy (from 52.3% to 88.2%) of sumatriptan. Likewise, U-46619 (5 x 10(-9) M) also increased the potency (from pEC(50) of 5.9 to 6.6) and efficacy (from 51.8% to 92.1%) of sumatriptan in the saphenous vein. In contrast, equieffective concentrations of histamine (10(-7) M) and U-46619 (3 x 10(-9) M) failed to amplify contraction to sumatriptan in the basilar artery. Contraction to sumatriptan was inhibited by nitrendipine (10(-7) M) in the basilar artery but not in the saphenous vein, suggesting that different contractile signaling mechanisms are operating in these tissues. Furthermore, U-46619- and thrombin-induced contractility in the basilar artery were also not amplified by histamine, suggesting that lack of amplification of contraction in the basilar artery was not restricted to sumatriptan but was rather a characteristic of this cerebral vessel. These data suggest that in the in vivo plasma milieu sumatriptan will more markedly contract the peripheral saphenous vein than the basilar artery, a cerebral blood vessel.

Platelets activated by transient coronary occlusion exacerbate ischemia-reperfusion injury in rat hearts

Platelets (Plt) accumulate in reperfused myocardium but their effect on myocardial necrosis has not been established. We tested the hypothesis that the effect of Plt depends on their activation status. Pig Plt were obtained before 48 min of coronary occlusion (pre-CO-Plt), 10 min after reperfusion (R-Plt), or after a 60-min sham operation (sham-Plt). Plt were infused into isolated rat hearts (n = 124) and subsequently submitted to 60 min of ischemia and 60 min of reperfusion. P-selectin expression was higher (P = 0.02) in R-Plt than in pre-CO-Plt or sham-Plt. Lactate dehydrogenase (LDH) release during reperfusion was similar in hearts receiving pre-CO-Plt, sham-Plt, or no Plt, but R-Plt increased LDH release by 60% (P = 0.004). Activation of pre-CO-Plt with thrombin increased P-selectin expression and LDH release (P < 0.001), and these results were unaffected by tirofiban. There was a close correlation between P-selectin expression and LDH release (r = 0.84; P < 0.001), and myocardial Plt accumulation (r = 0.85; P < 0.001). We conclude that the deleterious effect of Plt on reperfused myocardium depends on their activation status as represented by P-selectin expression, which is enhanced by ischemia-reperfusion.

Serotonin 5-HT(3) receptors on mechanosensitive neurons with cardiac afferents

In rats, the mechanosensitive cardiorenal baroreflex influencing renal excretory function might be impaired by serotonin occurring in coronary arteries, e.g., in hypertension. Because the afferent limb of this reflex could be affected, we investigated the responses of nodose ganglion cells (one neuron of reflex) to osmotic, mechanical stress in presence or absence of the serotonin 5-HT(3) receptor agonist phenylbiguanide (PBG). Current-voltage relationships (from -100 to +50 mV) were obtained using cell patch recordings while the cells were exposed to control or hypoosmotic solutions to induce mechanical stress. This protocol was repeated after low doses of PBG (10 microM), angiotensin II (10 nM), or the stretch-activated channel blocker gadolinium (20 microM) were added to the extracellular medium (EM). Hypoosmotic EM induced significant changes in cellular conductance. The full-range current-voltage relationship allowed for the calculation of a mean reversal potential of -13 +/- 1.2 mV with respect to this change in cellular conductance (n = 44). This increase in conductance was impaired after addition of either PBG or gadolinium to the EM,which was statistically evaluated at a voltage of -80 mV, where influences of voltage-gated channels are not likely to interfere with the responses recorded. The serotonin 5-HT(3) receptor antagonist tropisetron (10 nM) prevented the PBG effect on conductance responses. Angiotensin II had no influence. Hence, serotonin might decrease the mechanical sensitivity of afferent cardiac nerves controlling renal sympathetic nerve activity.

Effects of acute hormone therapy on recurrent ischemia in postmenopausal women with unstable angina

OBJECTIVES

We tested whether acute hormone therapy reduces ambulatory electrocardiographic ischemia in postmenopausal (PMP) women with unstable angina (UA).

BACKGROUND

Endothelial dysfunction contributes to the pathophysiology of UA. Acute estrogen administration improves endothelial function in PMP women with coronary artery disease and increases coronary artery blood flow.

METHODS

Two hundred ninety-three PMP women with UA (mean age 69.7 years), treated with standard anti-ischemic therapy, were enrolled within 24 h of symptom onset. In a double-blind fashion, subjects were randomized to receive intravenous followed by oral conjugated estrogen for 21 days, intravenous estrogen followed by oral conjugated estrogen plus medroxyprogesterone for 21 days or placebo. The primary end point was the number of ambulatory electrocardiographic ischemic events over the first 48 h. Clinical events were also determined over six months of follow-up.

RESULTS

Electrocardiographic ischemia did not differ among the three randomized groups. The mean number of ischemic events per patient over 48 h was 0.74 for estrogen, 0.86 for estrogen plus progesterone and 0.74 for the placebo groups (p = 0.87). The percentage of patients with ischemic events and the mean duration of ischemia did not differ between hormone- and placebo-treated patients. In-hospital and six-month rates of adverse clinical events were also similar among the three randomized groups.

CONCLUSIONS

Acute hormone therapy does not reduce ischemia in PMP women with UA when added to standard anti-ischemic therapy.

Lack of effect of glycoprotein IIb/IIIa blockade on myocardial platelet or polymorphonuclear leukocyte accumulation and on infarct size after transient coronary occlusion in pigs

OBJECTIVES

We sought to assess the effect of glycoprotein (GP) IIb/IIIa blockade on myocardial platelet and polymorphonuclear leukocyte accumulation and on infarct size after coronary injury and transient coronary occlusion (CO) in pigs.

BACKGROUND

It has been suggested that platelet GP IIb/IIIa blockade might reduce the severity of microvascular damage after reperfusion.

METHODS

Sixteen thiopental-anesthetized, open-chest pigs, in whom platelets had been labeled with technetium-99m (99mTc) on the previous day, were submitted to catheter-induced left anterior descending coronary artery (LAD) injury followed by 55 min of CO and 5 h of reperfusion. Five minutes before reflow, the animals were blindly allocated to receive lamifiban (intravenous bolus of 250 microg/kg body weight and continuous infusion of 3 microg/kg per min) or saline.

RESULTS

Lamifiban had a rapid and potent platelet anti-aggregatory effect, as demonstrated by significant prolongation of the bleeding time and profound (approximately 90%) inhibition of ex vivo platelet aggregation, and completely prevented the development of cyclic flow reductions of the LAD (0 vs. 5 +/- 1, one of them followed by re-occlusion, in control animals, p = 0.005). However, compared with animals receiving placebo, those treated with lamifiban had a similar (p = NS) content of (99m)Tc platelets in the reperfused myocardium (288 +/- 40% vs. 205 +/- 27% of the value in the control region, respectively) and similar myeloperoxidase activity (0.50 +/- 0.17 U/g vs. 0.47 +/- 0.17 U/g, respectively) and infarct size (46.8 +/- 12.0% vs. 49.8 +/- 10.5% of the area at risk, respectively). Arteriolar platelet thromboemboli were very rarely seen on histologic analysis. Lamifiban did not modify platelet P-selectin expression in additional studies.

CONCLUSIONS

Platelet GP IIb/IIIa blockade has a potent antithrombotic effect at the culprit lesion, but does not significantly reduce the magnitude of microvascular platelet accumulation or myocardial damage after transient CO.