Microvascular Vasoconstriction Research Articles

THE EFFECT OF CONCENTRIC AND ECCENTRIC CYCLING ON SKIN MICROVASCULATURE STRUCTURE AND FUNCTION IN INDIVIDUALS WITH HEART FAILURE: AN OPTICAL COHERENCE TOMOGRAPHY STUDY

INTRODUCTION Chronic heart failure (CHF) is associated with systemic vasoconstriction and exercise is an integral management strategy. Beneficial adaptations to exercise training in conduit arteries in CHF are well-established, but training-induced alteration in skin microvessels has not been explored, partly due to measurement limitations. Furthermore, the optimal type of exercise for individuals with CHF is not fully determined. This study utilised optical coherence tomography (OCT) to visualise, quantify and compare skin microvessel adaptations to eccentric (ECC) and concentric (CON) cycling interventions. METHODS Patients with CHF (EF<50%) were randomly assigned to either CON or ECC, and both groups underwent supervised training twice weekly for 16wks. Skin microvessel reactivity was measured at week 0 and week 16 using OCT responses to a local heating challenge alongside laser Doppler flowmetry (LDF). RESULTS Nineteen participants (CON n=9; ECC n=10, age 56.7±14.4yrs) completed the intervention. For OCT outcomes, there were no significant within group changes in skin local heating response from Wk0–Wk16 for either CON (Δdiameter: 14.2±3.3 µm vs 13.4±4.5 µm; Δvelocity: 107.6±31.8 µm.s-1 vs 106.4±36.4 µm.s-1; Δflow: 318.8±115.3 pl.s-1 vs 325.0±144.4 pl.s-1; Δdensity: 18.8±4.6% vs 16.5±2.6%) or ECC (Δdiameter: 13.5±4.0 µm vs 11.6±3.3 µm; Δvelocity: 105.9±33.6 µm.s-1 vs 126.3±29.6 µm.s-1; Δflow: 298.4±130.1 pl.s-1 vs 348.1±109.2 pl.s-1; Δdensity: 18.0±5.4% vs 17.5±2.1%), all P>0.050. There were no other differences between groups in response to training (all P>0.05). No significant differences were found in response to local heating by LDF (P>0.05). There were no differences in these variables between groups in response to training (all P>0.050) and no differences in LDF responses (P>0.050). CONCLUSIONS The 16-week cycle exercise program implemented in this study was insufficient to induce any evidence of microvascular adaptation in patients with CHF. Overcoming cutaneous microvascular vasoconstriction in CHF may require more aggressive exercise approaches than those which have induced adaptation in conduit and resistance arterioles.

Abstract 17167: Uncontrolled Hypertension Increases Endothelin-1-Induced Contractile Response of Coronary Microvasculature Both Before and After Cardioplegia and Cardiopulmonary Bypass

Introduction: Hypertensive patients undergoing cardiopulmonary bypass (CPB) have worse clinical outcomes, and coronary microvascular dysfunction may play a role. Endothelin-1 (ET-1), a vasoactive biopeptide, is increased in cardiomyocytes during the hypertrophic response to hypertension and in patients following CPB. Differential effects of hypertension on coronary microvascular reactivity and molecular signaling pathways following CPB have yet to be elucidated. Aims: This study investigated the effects of well-controlled and uncontrolled hypertension on CPB-induced changes in coronary microvascular vasoconstriction to ET-1 and associated signaling using unique in vitro microvascular reactivity studies, RNA deep sequencing, and established molecular methods. Methods: Coronary microvessels (<200um) were harvested from atrial samples from patients with no hypertension (NH), well-controlled hypertension (CH), and uncontrolled hypertension (UH) before and after CPB. In vitro contractile response to ET-1 was assessed using video microscopy. Protein expression and receptor localization were measured using immunoblotting and immunohistochemistry, respectively. Enzyme-linked immunosorbent assay was used to quantify plasma concentration of ET-1. Results: Pre-CPB contractile response of coronary microvessels to ET-1 in UH was increased compared to NH or CH (p <0.05). Post-CPB contractile response was impaired overall (p <0.05). Between groups, contractile response in CH and NH was comparable while response in UH was higher (p <0.05). Plasma ET-1 increased post-CPB (p = 0.18). Total protein levels and localization of ET A R and ET B R were unchanged post-CPB. Conclusions: While CPB overall blunted vasomotor contractile response of coronary microvessels to ET-1, UH was associated with relatively increased vasoconstriction compared to CH and NH. Changes in plasma ET-1, ET A R and ET B R levels or localization did not contribute to these effects.

Plasma resuscitation improves and restores intestinal microcirculatory physiology following haemorrhagic shock.

Intestinal ischaemia-reperfusion injury following resuscitated haemorrhagic shock (HS) leads to endothelial and microcirculatory dysfunction and intestinal barrier breakdown. Although vascular smooth muscle machinery remains intact, microvascular vasoconstriction occurs secondary to endothelial cell dysfunction, resulting in further ischaemia and organ injury. Resuscitation with fresh frozen plasma (FFP) improves blood flow, stabilizes the endothelial glycocalyx and alleviates organ injury. We postulate these improvements correlate with decreased tissue CO2 concentrations, improved microvascular oxygenation and attenuation of intestinal microvascular endothelial dysfunction. Male Sprague-Dawley rats were randomly assigned to groups (n = 8/group): (1) sham, (2) HS (40% mean arterial blood pressure [MAP], 60 min) + crystalloid resuscitation (CR) (shed blood saline) and (3) HS + FFP (shed blood + FFP). MAP, heart rate (HR), ileal perfusion, pO2 and pCO2 were measured at intervals until 4 h post-resuscitation (post-RES). At 4 h post-RES, the ileum was rinsed in situ with Krebs solution. Topical acetylcholine and then nitroprusside were applied for 10 min each. Serum was obtained, and after euthanasia, tissues were harvested and snap-frozen in liquid N2 and stored at -80°C. FFP resuscitation resulted in sustained ileal perfusion as well as rapid sustained return to baseline microvascular pO2 and pCO2 values when compared to CR (p < 0.05). Endothelial function was preserved relative to sham in the FFP group but not in the CR group (p < 0.05). FFP-based resuscitation improves intestinal perfusion immediately following resuscitation, which correlates with improved tissue oxygenation and decreased tissue CO2 levels. CR resulted in significant damage to endothelial vasodilation response to acetylcholine, while FFP preserved this function.

Real world single center experience with saphenous vein grafts interventions: should filters be filtered out?

Percutaneous coronary intervention (PCI) of saphenous vein grafts (SVG) can be challenging due to no reflow phenomenon from distal embolization of debris and microvascular vasoconstriction, resulting in myocardial injury post-procedure. Guidelines promote the use of distal embolic protection devices (EPD) to protect the distal arterial bed during SVG PCI. However, this approach has shown less-than-optimal results in many studies. We report our data using the Borgess protocol [prophylactic intracoronary (IC) nicardipine injection and direct stenting], as an alternative to EPDs in a large series of SVG interventions. This is a retrospective, cohort study of our single center experience with SVG interventions between 2017 and 2021. The primary outcome of the study was major adverse cardiovascular events (MACE) [a composite of death, emergent coronary artery bypass graft surgery (CABG), myocardial infarction (MI), and target vessel revascularization (TVR)] at 30 days post-procedure. There were 424 consecutive SVG interventions performed during the study period, and 76% of cases presented with acute coronary syndrome. Full adherence to the Borgess protocol was observed in 36% of cases; IC nicardipine was utilized in 72% of cases. MACE rate was 3.5% at 30 days driven primarily by MI (2.6%). The Borgess protocol approach to vein graft interventions proved good outcomes when compared to SVG PCI in randomized trials utilizing EPDs. Our study is limited by the retrospective nature and single center experience.

The Impact of Mental Stress on Cardiovascular Health-Part II.

Endothelial dysfunction is one of the earliest manifestations of atherosclerosis, contributing to its development and progression. Mental stress induces endothelial dysfunction through increased activity of the sympathetic nervous system, release of corticotropin-releasing hormone from the hypothalamus, inhibition of nitric oxide (NO) synthesis by cortisol, and increased levels of pro-inflammatory cytokines. Mental-stress-induced increased output of the sympathetic nervous system and concomitant withdrawal of the parasympathetic inflammatory reflex results in systemic inflammation and activation of a neural–hematopoietic–arterial axis. This includes the brainstem and subcortical regions network, bone marrow activation, release of leukocytes into the circulation and their migration to the arterial wall and atherosclerotic plaques. Low-grade, sterile inflammation is involved in all steps of atherogenesis, from coronary plaque formation to destabilisation and rupture. Increased sympathetic tone may cause arterial smooth-muscle-cell proliferation, resulting in vascular hypertrophy, thus contributing to the development of hypertension. Emotional events also cause instability of cardiac repolarisation due to brain lateralised imbalance of cardiac autonomic nervous stimulation, which may lead to asymmetric repolarisation and arrhythmia. Acute emotional stress can also provoke severe catecholamine release, leading to direct myocyte injury due to calcium overload, known as myocytolysis, coronary microvascular vasoconstriction, and an increase in left ventricular afterload. These changes can trigger a heart failure syndrome mimicking acute myocardial infarction, characterised by transient left ventricular dysfunction and apical ballooning, known as stress (Takotsubo) cardiomyopathy. Women are more prone than men to develop mental-stress-induced myocardial ischemia (MSIMI), probably reflecting gender differences in brain activation patterns during mental stress. Although guidelines on CV prevention recognise psychosocial factors as risk modifiers to improve risk prediction and decision making, the evidence that their assessment and treatment will prevent CAD needs further evaluation.

Cortical spreading depolarizations in the context of subarachnoid hemorrhage and the role of ketamine

Delayed cerebral ischemia (DCI) is one of the main complications of spontaneous subarachnoid haemorrhage and one of its causes is the cortical spreading depolarizations (CSDs). Cortical spreading depolarizations are waves of neuronal and glial depolarizations in which there is loss of neuronal ionic homeostasis with potassium efflux and sodium and calcium influx. In damaged brain areas and brain areas at risk, such as those adjacent to subarachnoid haemorrhage (SAH), CSDs induce microvascular vasoconstriction and, therefore, hypoperfusion and spread of ischemia. Several studies have been devoted to minimize secondary injuries that occur hours to days after an acute insult. Ketamine, a drug until recently contraindicated in the neurosurgical population for potentially causing intracranial hypertension, has re-emerged as a potential neuroprotective agent due to its pharmacodynamic effects at the cellular level. These effects include anti-inflammatory mechanisms, and those of microthrombosis and cell apoptosis controls, and of modulation of brain excitotoxicity and CSDs. A literature review was performed at PubMed covering the period from 2002 to 2019. Retrospective studies confirmed the effects of ketamine on the control of CSDs and, consequently, of DCI in patients with SAH, but did not show improvement in clinical outcome. The influence of ketamine on the occurrence/development of DCI needs to be further confirmed in prospective randomized studies.

Combating hypoxemia in COVID-19 patients with a natural oxygen carrier, HEMO2Life® (M101)

BackgroundInfection with SARS-CoV-2 is responsible for the COVID-19 crisis affecting the whole world. This virus can provoke acute respiratory distress syndrome (ARDS) leading to overcrowed the intensive care unit (ICU). Over the last months, worldwide experience demonstrated that the ARDS in COVID-19 patients are in many ways “atypical”. The mortality rate in ventilated patients is high despite the application of the gold standard treatment (protective ventilation, curare, prone position, inhaled NO). Several studies suggested that the SARS-CoV-2 could interact negatively on red blood cell homeostasis. Furthermore, SarsCov2 creates Reactive Oxygen Species (ROS), which are toxic and generate endothelial dysfunction. Hypothesis/objective(s)We hypothesis that HEMO2Life® administrated intravenously is safe and could help symptomatically the patient condition. It would increase arterial oxygen content despite lung failure and allow better tissue oxygenation control. The use of HEMO2Life® is also interesting due to its anti-oxidative effect preventing cytokine storm induced by the SARS-CoV-2. Evaluation of the hypothesis: Hemarina is based on the properties of the hemoglobin of the Arenicola marina sea-worm (HEMO2Life®). This extracellular hemoglobin has an oxygen capacity 40 times greater than the hemoglobin of vertebrates. Furthermore, the size of this molecule is 250 times smaller than a human red blood cell, allowing it to diffuse in all areas of the microcirculation, without diffusing outside the vascular sector. It possesses an antioxidative property du a Superoxide Dismutase Activity. This technology has been the subject of numerous publications and HEMO2Life® was found to be well-tolerated and did not induce toxicity. It was administered intravenously to hamsters and rats, and showed no acute effect on heart rate and blood pressure and did not cause microvascular vasoconstriction. In preclinical in vivo models (mice, rats, and dogs), HEMO2Life® has enabled better tissue oxygenation, especially in the brain. This molecule has already been used in humans in organ preservation solutions and the patients showed no abnormal clinical signs. Consequences of the hypothesisThe expected benefits of HEMO2Life® for COVID-19 patients are improved survival, avoidance of tracheal intubation, shorter oxygen supplementation, and the possibility of treating a larger number of patients as molecular respirator without to use an invasive machine.

Endothelin receptor heteromerization inhibits β-arrestin function in HEK293 cells.

The endothelin receptor A (ETA) and endothelin receptor B (ETB) are G protein-coupled receptors that are co-expressed in vascular smooth muscle cells. Endothelin-1 (ET-1) activates endothelin receptors to cause microvascular vasoconstriction. Previous studies have shown that heteromerization between ETA and ETB prolongs Ca2+ transients, leading to prolongation of Gαq-dependent signaling and sustained vasoconstriction. We hypothesized that these effects are in part mediated by the resistance of ETA/ETB heteromers to β-arrestin recruitment and subsequent desensitization. Using bioluminescence resonance energy transfer 2 (BRET2), we found that ETB has a relatively equal affinity to form either homomers or heteromers with ETA when co-expressed in the human embryonic kidney 293 (HEK293) cells. When co-expressed, activation of ETA and ETB by ET-1 caused a heteromer-specific reduction and delay in β-arrestin-2 recruitment with a corresponding reduction and delay in ET-1-induced ETA/ETB co-internalization. Furthermore, the co-expression of ETA and ETB inhibited ET-1-induced β-arrestin-1-dependent extracellular signal-regulated kinase (ERK) phosphorylation while prolonging ET-1-induced Gαq-dependent ERK phosphorylation. ETA/ETB heteromerization mediates the long-lasting vasoconstrictor response to ET-1 by the prolongation of Gαq-dependent signaling and inhibition of β-arrestin function.

Apohemoglobin-haptoglobin complex attenuates the pathobiology of circulating acellular hemoglobin and heme.

Haptoglobin (Hp) is the plasma protein that binds and clears cell-free hemoglobin (Hb), whereas apohemoglobin (apoHb, i.e., Hb devoid of heme) can bind heme. Therefore, the apoHb-Hp protein complex should facilitate holoHb-apoHb αβ-dimer exchange and apoHb-heme intercalation. Thus, we hypothesized that apoHb-Hp could facilitate both Hb and heme clearance, which, if not alleviated, could have severe microcirculatory consequences. In this study, we characterized apoHb-Hp and Hb/heme ligand interactions and assessed their in vivo consequences. Hb exchange and heme binding with the apoHb-Hp complex was studied with transfer assays using size-exclusion high-performance liquid chromatography coupled with UV-visible spectrophotometry. Exchange/transfer experiments were conducted in guinea pigs dosed with Hb or heme-albumin followed by a challenge with equimolar amounts of apoHb-Hp. Finally, systemic and microcirculatory parameters were studied in hamsters instrumented with a dorsal window chamber via intravital microscopy. In vitro and in vivo Hb exchange and heme transfer experiments demonstrated proof-of-concept Hb/heme ligand transfer to apoHb-Hp. Dosing with the apoHb-Hp complex reversed Hb- and heme-induced systemic hypertension and microvascular vasoconstriction, reduced microvascular blood flow, and diminished functional capillary density. Therefore, this study highlights the apoHb-Hp complex as a novel therapeutic strategy to attenuate the adverse systemic and microvascular responses to intravascular Hb and heme exposure.NEW & NOTEWORTHY This study highlights the apoHb-Hp complex as a novel therapeutic strategy to attenuate the adverse systemic and microvascular responses to intravascular Hb and heme exposure. In vitro and in vivo Hb exchange and heme transfer experiments demonstrated proof-of-concept Hb/heme ligand transfer to apoHb-Hp. The apoHb-Hp complex reverses Hb- and heme-induced systemic hypertension and microvascular vasoconstriction, preserves microvascular blood flow, and functional capillary density. In summary, the unique properties of the apoHb-Hp complex prevent adverse systemic and microvascular responses to Hb and heme-albumin exposure and introduce a novel therapeutic approach to facilitate simultaneous removal of extracellular Hb and heme.

High Levels of Peripheral Vasoconstriction Detected By Polysomnography Predict More Acute Severe Pain Episodes in Children with Sickle Cell Anemia

Sickle cell anemia (SCA) is genetic disease associated with chronic hemolysis and severe vaso-occlusive pain. Triggers for vaso-occlusive pain include both extreme temperatures (hot and cold), and stress. Our prior work demonstrates that anticipatory pain, experimental pain, experimental mental stress, and cold exposure cause significant global vasoconstriction in SCA and vasoconstriction responses differ among subjects.Anything that decreases microvascular flow will increase the likelihood that the red blood cells will not escape the microvasculature before deoxyhemoglobin S (HbS) polymerizes, leading to vaso-occlusion. However, this theoretical model has not been proven at a macro scale in patients. We showed that hypoxia induced in SCA subjects causes loss of parasympathetic modulation of heart rate but not decreased microvascular flow. Consistent with this, a prospective cohort study of SCA subjects showed no significant association between low mean nocturnal SpO2 and the incidence of VOC. However, surges in sympathetic activity accompany transient arousals and respiratory events during sleep, and lead to varying levels of peripheral vasoconstriction. In a prospective NIH funded cohort study of children with SCA, we tested the hypothesis that children with SCA and high levels when compared to low levels of intrinsic microvascular vasoreactivity (based on vasoconstriction events detected by polysomnography (PSG)) have a higher incidence rate of severe vaso-occlusive pain that requires hospitalization within 6 months of the PSG. We analyzed the time-series of R-R intervals (RRI) derived from the electrocardiogram and beat-to-beat amplitudes of finger photoplethysmography reflecting peripheral blood flow (PPGa) derived from the scored PSGs and clinical records of 212 children, who participated in the multi-center prospective SCA cohort study reported by Willen et al. (Am J Hematol 2018; 93:478-485). Vasoconstriction events were detected by applying an algorithm that found reductions in PPGa from local baseline that exceeded a threshold level of change. The changes in RRI from the pre-vasoconstriction baseline were also computed (Fig 1). The duration, average magnitude (Mvasoc) and area under the curve of PPGa were extracted from each significant vasoconstriction. The median values of these compact descriptors were taken to represent the nocturnal vasoconstriction characteristics of each participant. A participant was classified to be in the high- or low-pain event category if they were hospitalized for severe pain at least two times or less than 2 times within a 1-year window from 6 months before to 6 months after the PSG, respectively. Multiple logistic regression analysis was applied, using pain category as the outcome variable, and vasoconstriction descriptors, arousal index, obstructive apnea-hypopnea index, age, sex and hemoglobin level as predictor variables. Pain category was strongly associated with magnitude of vasoconstriction (Mvasoc; p=0.0058), with larger Mvasoc predicting high-pain, after accounting for age, sex and hemoglobin level (Hgb). Figure 2 displays the adjusted Mvasoc (mean ± SE) in the high-pain and low/no-pain groups. Mvasoc was strongly correlated with arousal index (p=0.0073). However, none of the traditional measures of sleep-disordered breathing, including arousal index, were associated with pain category. Age was the only other predictor of severe pain. These findings, showing that propensity for a high degree of microvascular vasoconstriction is associated with the temporal relationship of severe pain requiring hospitalization, validate on a macro scale the model that increased microvascular transit time promotes entrapment of sickled red blood cells, elevating the risk of severe vaso-occlusive pain. Our data reveals for the first time, a mechanistic link between the patient's symptoms and the triggering of transition from steady state to acute severe pain. The fact that individuals have intrinsic vasoreactivity phenotypes, that can be identified by analysis of the photoplethysmogram, provides yet another factor in acute vaso-occlusive pain. Autonomic balance and vasoreactivity likely contribute to known variability of the incidence rate of severe pain and represent another plausible target for therapeutic intervention. Disclosures Coates: apo pharma: Consultancy, Honoraria, Speakers Bureau; vifor: Consultancy, Honoraria; agios pharma: Consultancy, Honoraria; celgene: Consultancy, Honoraria, Other: steering committee of clinical study.

Relationship between skin blood flow regulation mechanisms and vascular endothelial growth factor in patients with metabolic syndrome.

The focus of this paper is the determination of endothelial dysfunction in patients with metabolic syndrome (MetS) and the establishment of a relationship between the traditional biomarkers of endothelial dysfunction and the vascular tone regulation indices obtained from indirect cold tests in MetS patients. Our investigation was conducted on 30 patients aged 45.5±9 years. The control group comprised 14 healthy subjects aged 48.2±2.4 years. The mechanism of vascular tone regulation was investigated using the wavelet analysis of skin temperature oscillations (WAST). The degrees of microvascular vasoconstriction and vasodilatation were determined during contralateral cold tests in the endothelial (0.02-0.0095 Hz), neurogenic (0.05-0.02 Hz) and myogenic (0.05-0.14 Hz) frequency ranges. In MetS patients, vasoconstriction indices were higher and vasodilatation indices were lower than in the subjects of the control group, which is indicative of disorders in the mechanisms of microvascular tone regulation. These indices correlate with the metabolic parameters and VEGF (vascular endothelial growth factor) levels. The correlation of vasoconstriction and vasodilatation indices with the main factors of the metabolic syndrome testifies that the biological and functional aspects of the endothelial dysfunction are closely related.

Does red blood cell irradiation and/or anemia trigger intestinal injury in premature infants with birth weight\u2009\u2264\u20091250\xa0g? An observational birth cohort study

BackgroundNecrotizing enterocolitis (NEC) is a leading cause of neonatal morbidity and mortality in premature infants. To date, no effective biomarkers exist to predict which premature infants will develop NEC, limiting targeted prevention strategies. Multiple observational studies have reported an association between the exposure to red blood cell (RBC) transfusion and/or anemia and the subsequent development of NEC; however, the underlying physiologic mechanisms of how these factors are independently associated with NEC remain unknown.MethodsIn this paper, we outline our prospective, multicenter observational cohort study of infants with a birth weight ≤ 1250 g to investigate the associations between RBC transfusion, anemia, intestinal oxygenation and injury that lead to NEC. Our overarching hypothesis is that irradiation of RBC units followed by longer storage perturbs donor RBC metabolism and function, and these derangements are associated with paradoxical microvascular vasoconstriction and intestinal tissue hypoxia increasing the risk for injury and/or NEC in transfused premature infants with already impaired intestinal oxygenation due to significant anemia. To evaluate these associations, we are examining the relationship between prolonged irradiation storage time (pIST), RBC metabolomic profiles, and anemia on intestinal oxygenation non-invasively measured by near-infrared spectroscopy (NIRS), and the development of NEC in transfused premature infants.DiscussionOur study will address a critical scientific gap as to whether transfused RBC characteristics, such as irradiation and metabolism, impair intestinal function and/or microvascular circulation. Given the multifactorial etiology of NEC, preventative efforts will be more successful if clinicians understand the underlying pathophysiologic mechanisms and modifiable risk factors influencing the disease.Trial registrationOur study is registered in ClinicalTrials.gov Identifier: NCT02741648.

β1-Subunit of the calcium-sensitive potassium channel modulates the pulmonary vascular smooth muscle cell response to hypoxia.

Accessory subunits associated with the calcium-sensitive potassium channel (BKCa), a major determinant of vascular tone, confer functional and anatomical diversity. The β1 subunit increases Ca2+ and voltagesensitivity of the BKCa channel and is expressed exclusively in smooth muscle cells. Evidence supporting the physiological significance of the β1 subunit includes the observations that murine models with deletion of the β1 subunit are hypertensive and that humans with a gain-of-function β1 mutation are at a decreased risk of diastolic hypertension. However, whether the β1 subunit of the BKCa channel contributes to the low tone that characterizes the normal pulmonary circulation or modulates the pulmonary vascular response to hypoxia remains unknown. To determine the role of the BKCa channel β1 subunit in the regulation of pulmonary vascular tone and the response to acute and chronic hypoxia, mice with deletion of the Kcnmb1 gene that encodes for the β1 subunit ( Kcnmb1-/-) were placed in chronic hypoxia (10% O2) for 21-24 days. In normoxia, right ventricular systolic pressure (RVSP) did not differ between Kcnmb1+/+ (controls) and Kcnmb1-/- mice. After exposure to either acute or chronic hypoxia, RVSP was higher in Kcnmb1-/- mice compared with Kcnmb1+/+ mice, without increased vascular remodeling. β1 subunit expression was predominantly confined to pulmonary artery smooth muscle cells (PASMCs) from vessels ≤ 150 µm. Peripheral PASMCs contracted collagen gels irrespective of β1 expression. Focal adhesion expression and Rho kinase activity were greater in Kcnmb1-/- compared with Kcnmb1+/+ PASMCs. Compromised PASMC β1 function may contribute to the heightened microvascular vasoconstriction that characterizes pulmonary hypertension.

Mechanisms of sphingosine-1-phosphate-mediated vasoconstriction of rat afferent arterioles.

Sphingosine-1-phosphate (S1P) influences resistance vessel function and is implicated in renal pathological processes. Previous studies revealed that S1P evoked potent vasoconstriction of the pre-glomerular microvasculature, but the underlying mechanisms remain incompletely defined. We postulated that S1P-mediated pre-glomerular microvascular vasoconstriction involves activation of voltage-dependent L-type calcium channels (L-VDCC) and the rho/rho kinase pathway. Afferent arteriolar reactivity was assessed in vitro using the blood-perfused rat juxtamedullary nephron preparation, and diameter was measured during exposure to physiological and pharmacological agents. Exogenous S1P (10-9 -10-5 mol L-1 ) evoked concentration-dependent vasoconstriction of afferent arterioles. Superfusion with nifedipine, a L-VDCC blocker, increased arteriolar diameter by 39 ± 18% of baseline and significantly attenuated the S1P-induced vasoconstriction. Superfusion with the rho kinase inhibitor, Y-27632, increased diameter by 60 ± 12% of baseline and also significantly blunted vasoconstriction by S1P. Combined nifedipine and Y-27632 treatment significantly inhibited S1P-induced vasoconstriction over the entire concentration range tested. In contrast, depletion of intracellular Ca2+ stores with the Ca2+ -ATPase inhibitors, thapsigargin or cyclopiazonic acid, did not alter the S1P-mediated vasoconstrictor profile. Scavenging reactive oxygen species (ROS) or inhibition of nicotinamide adenine dinucleotide phosphate oxidase activity significantly attenuated S1P-mediated vasoconstriction. Exogenous S1P elicits potent vasoconstriction of rat afferent arterioles. These data also demonstrate that S1P-mediated pre-glomerular vasoconstriction involves activation of L-VDCC, the rho/rho kinase pathway and ROS. Mobilization of Ca2+ from intracellular stores is not required for S1P-mediated vasoconstriction. These studies reveal a potential role for S1P in the modulation of renal microvascular tone.

Ischaemia-reperfusion injury and hyperbaric oxygen pathways: a review of cellular mechanisms.

Ischaemia-induced tissue injury has wide-ranging clinical implications including myocardial infarction, stroke, compartment syndrome, ischaemic renal failure and replantation and revascularization. However, the restoration of blood flow produces a 'second hit' phenomenon, the effect of which is greater than the initial ischaemic event and characterizes ischaemia-reperfusion (IR) injury. Some examples of potential settings of IR injury include: following thrombolytic therapy for stroke, invasive cardiovascular procedures, solid organ transplantation, and major trauma resuscitation. Pathophysiological events of IR injury are the result of reactive oxygen species (ROS) production, microvascular vasoconstriction, and ultimately endothelial cell-neutrophil adhesion with subsequent neutrophil infiltration of the affected tissue. Initially thought to increase the amount of free radical oxygen in the system, hyperbaric oxygen (HBO) has demonstrated a protective effect on tissues by influencing the same mechanisms responsible for IR injury. Consequently, HBO has tremendous therapeutic value. We review the biochemical mechanisms of ischaemia-reperfusion injury and the effects of HBO following ischaemia-reperfusion.

Polyethylene Glycol Camouflaged Earthworm Hemoglobin.

Nearly 21 million components of blood and whole blood and transfused annually in the United States, while on average only 13.6 million units of blood are donated. As the demand for Red Blood Cells (RBCs) continues to increase due to the aging population, this deficit will be more significant. Despite decades of research to develop hemoglobin (Hb) based oxygen (O2) carriers (HBOCs) as RBC substitutes, there are no products approved for clinical use. Lumbricus terrestris erythrocruorin (LtEc) is the large acellular O2 carrying protein complex found in the earthworm Lumbricus terrestris. LtEc is an extremely stable protein complex, resistant to autoxidation, and capable of transporting O2 to tissue when transfused into mammals. These characteristics render LtEc a promising candidate for the development of the next generation HBOCs. LtEc has a short half-life in circulation, limiting its application as a bridge over days, until blood became available. Conjugation with polyethylene glycol (PEG-LtEc) can extend LtEc circulation time. This study explores PEG-LtEc pharmacokinetics and pharmacodynamics. To study PEG-LtEc pharmacokinetics, hamsters instrumented with the dorsal window chamber were subjected to a 40% exchange transfusion with 10 g/dL PEG-LtEc or LtEc and followed for 48 hours. To study the vascular response of PEG-LtEc, hamsters instrumented with the dorsal window chamber received multiple infusions of 10 g/dL PEG-LtEc or LtEc solution to increase plasma LtEc concentration to 0.5, then 1.0, and 1.5 g/dL, while monitoring the animals’ systemic and microcirculatory parameters. Results confirm that PEGylation of LtEc increases its circulation time, extending the half-life to 70 hours, 4 times longer than that of unPEGylated LtEc. However, PEGylation increased the rate of LtEc oxidation in vivo. Vascular analysis verified that PEG-LtEc showed the absence of microvascular vasoconstriction or systemic hypertension. The molecular size of PEG-LtEc did not change the colloid osmotic pressure or blood volume expansion capacity compared to LtEc, due to LtEc’s already large molecular size. Taken together, these results further encourage the development of PEG-LtEc as an O2 carrying therapeutic.

Influence of sympathetic activity in the control of peripheral microvascular tone in preterm infants.

Microvascular dysregulation following preterm birth is associated with increased illness severity and hypotension, particularly in males. Sympathetic nervous vascular regulation is evident in females. We hypothesized that sympathetic dysfunction in male preterm infants may contribute to a failure of peripheral microvascular vasoconstriction. Microvascular blood flow of infants 24-43 wk gestational age was assessed at 6, 24, and 72 h of age by laser Doppler. Blood flow Fourier transformed frequency distribution spectra (low frequency/high frequency ratio) were used to assess the influence of sympathetic tone on microvascular regulation. Total sympathetic output was assessed as urinary normetanephrine. Microvascular sympathetic activity at 24 h postnatal age decreased in early preterm males, but not females. Peripheral sympathetic activity increased with advancing postnatal age in females, but decreased in males. In early preterm infants, total normetanephrine outputs increase significantly with postnatal age, in both sexes. Sympathetic activation following preterm birth is sexually dimorphic, with preterm males having reduced sympathetic tone and reduced upregulation of sympathetic tone following birth. There is evidence of a disconnect between central sympathetic activity and local peripheral microcirculatory sympathetic drive. This may relate to autonomic nervous immaturity and highlights the need to understand how preterm birth may affect autonomic function.

Sublingual microvascular perfusion is altered during normobaric and hyperbaric hyperoxia

Hyperoxia and hyperbaric oxygen therapy can restore oxygen tensions in tissues distressed by ischemic injury and poor vascularization and is believed to also yield angiogenesis and regulate tissue perfusion. The aim of this study was to develop a model in which hyperoxia-driven microvascular changes could be quantified and to test the hypothesis that microcirculatory responses to both normobaric (NB) and hyperbaric (HB) hyperoxic maneuvers are reversible. Sublingual mucosa microcirculation vessel density, proportion of perfused vessels, vessel diameters, microvascular flow index, macrohemodynamic, and blood gas parameters were examined in male rabbits breathing sequential O2/air mixtures of 21%, 55%, 100%, and return to 21% during NB (1.0bar) and HB (2.5bar) conditions. The results indicate that NB hyperoxia (55% and 100%) produced significant decreases in microvascular density and vascular diameters (p<0.01 and p<0.05, respectively) accompanied by significant increases in systolic and mean arterial blood pressure (p<0.05, respectively) with no changes in blood flow indices when compared to NB normoxia. HB normoxia/hyperoxia resulted in significant decreases in microvascular density (p<0.05), a transient rise in systolic blood pressure at 55% (p<0.01), and no changes in blood vessel diameter and blood flow indices when compared to NB hyperoxia. All microcirculation parameters reverted back to normal values upon return to NB normoxia. We conclude that NB/HB hyperoxia-driven changes elicit reversible physiological control of sublingual mucosa blood perfusion in the presence of steady cardiovascular function and that the absence of microvascular vasoconstriction during HB conditions suggests a beneficial mechanism associated with maintaining peak tissue perfusion states.

Design and Rationale for the Endothelin-1 Receptor Antagonism in the Prevention of Microvascular Injury in Patients with non-ST Elevation Acute Coronary Syndrome Undergoing Percutaneous Coronary Intervention (ENDORA-PCI) Trial.

Peri-procedural myocardial infarction (PMI) occurs in a small but significant portion of patients undergoing percutaneous intervention (PCI). The underlying mechanisms are complex and may include neurohormonal activation and release of vasoactive substances resulting in disruption of the coronary microcirculation. Endothelin in particular has been found in abundance in atherosclerotic plaques and in systemic circulation following PCI, and may be a potential culprit for PMI through its action on microvascular vasoconstriction, and platelet and neutrophil activation. In this study we aim to characterize the behavior of the coronary microcirculation during a PCI with the index of microvascular resistance (IMR) and the effect of peri-procedural endothelin antagonism. The ENDORA-PCI trial is a randomized, double-blind, placebo-controlled, single-center clinical trial designed to evaluate the efficacy of endothelin antagonism in attenuating the peri-procedural rise in IMR as a surrogate marker for PMI. The patients of interest are those with non-ST elevation acute coronary syndrome (NSTEACS) undergoing PCI, and we aim to recruit 52 patients overall to give the study a power of 80% at an α level of 5%. Patients will be randomized in a 1:1 fashion to either Ambrisentan, an endothelin antagonist, or placebo, prior to their PCI. IMR will be measured before and after PCI. The primary endpoint is the difference in peri-procedural changes in patients' IMR between the two groups. The ENDORA-PCI study will investigate whether endothelin antagonism with Ambrisentan attenuates the peri-procedural rise in IMR in patients with NSTEACS undergoing PCI, and thus potentially the risk of PMI.

Abstract 17559: Norepinephrine Levels are Associated With the Magnitude of Vasoconstriction During Mental Stress

Background: Patients with CAD develop varying degrees of microvascular vasoconstriction in response to mental stress, leading to myocardial ischemia. Catecholamine increases during mental stress may explain this effect. We hypothesized, in a cohort of stable CAD patients, that increased epinephrine and norepinephrine levels from rest to peak mental stress predict peripheral microvascular vasoconstriction. Methods: We analyzed data from 204 patients with CAD and high quality vascular data. Subjects underwent a standardized mental stress test using a public speaking task. Peripheral arterial tonometry (PAT) was used to assess peripheral microvascular function during rest and mental stress. The PAT response was calculated as a ratio of the minimum pulse wave amplitude during the speaking task to the mean amplitude during rest. Plasma epinephrine and norepinephrine levels were obtained 15 minutes before and at peak mental stress. Linear regression modeling was used to adjust for potential confounders. Results: The mean (SD) age was 64 (8), 16% were women, and 28% were African American. Subjects in the quartile with the greatest vasoconstriction had the highest increase in norepinephrine levels (73.5 (31.4) ng/mL [mean (SEM]), while those in the quartile with the least vasoconstriction had decreased norepinephrine levels by 47.7 (32.5) ng/mL, p for trend&lt;0.001 (Figure). There was no significant association between PAT and epinephrine. After multivariable adjustment for sociodemographics, CAD risk factors, medical history, medication use, major depression, and PTSD, the association between the PAT ratio and norepinephrine remained significant (p=0.003). Conclusion: Changes in circulating norepinephrine, but not epinephrine levels predict peripheral microvascular vasoconstriction during mental stress.