Regional Blood Flow Research Articles

Renal potassium regulation in a pig model of therapeutic hypothermia

Therapeutic hypothermia is increasingly utilized clinically to reduce tissue metabolism and protect against neurological damage in cases of cardiac arrest, traumatic brain injury or perinatal hypoxic ischemia. With even mild exposure to hypothermia, hypokalemia develops purportedly due to transcellular potassium shifts resulting in decreased circulating potassium levels. Renal dysfunction with body temperature cooling has also been postulated to potentially contribute to development of sustained hypokalemia. In this study, we used a pig model of controlled acute hypothermia without confounding hypotension and hypoxemia, to test the hypothesis that renal handling of potassium remains intact in hypothermia and is not the cause of decreased circulating plasma potassium seen with body cooling. Anesthetized, mechanically ventilated Duroc cross young pigs (n=25, body weight = 10.0 ± 0.4 kg, male or female) were catheterized for hemodynamic monitoring, regional blood flow assessment via colored microspheres, and urine collection. After baseline values were obtained, pigs were divided into a control normothermia group (n=12) with body temperature maintained at 38.4 ± 0.1 oC or a hypothermia group (n=13) with core body temperature cooled to 34.5 ± 0.1 oC and hypothermia sustained for 2 hours. Hypothermia reduced tissue metabolism as indicated by a decrease in oxygen consumption (VO2= 5.2 ± 0.2 ml/kg in normothermia vs 3.7 ± 0.3 ml/kg in hypothermia. Mean arterial pressure (68± 3 mm Hg) and cardiac output (199 ± 21 ml/min/kg) were not different between groups. Even with the short duration of cold exposure, plasma potassium was lower (p<0.05) within 2 hours of hypothermia (4.1 ± 0.1 mEq/L) vs control (4.8 ± 0.1 mEq/L). Cold exposure caused redistribution of blood flow to the small intestines from other internal organs. Renal blood flow tended to decrease with cold, but glomerular filtration rate was suffcient to maintain urine flow, sodium excretion and free water clearance. Potassium clearance, however, was lower (p<0.05) in hypothermia (0.70 ± 0.07 ml/min/kg) than in normothermia (1.04 ± 0.07 ml/min/kg), with lower potassium excretion (hypothermia = 2997 ± 331 mEq/min vs control = 4784 ± 393 mEq/min, p<0.05) and fractional excretion of potassium. Reduced renal potassium excretion is consistent with renal compensation for lower circulating potassium induced by hypothermia. Interestingly, with relatively higher blood flow to the small intestines compared to decreased blood flow of other internal organs, potassium secretion in the early colon may contribute to further potassium wasting in hypothermia. The rapid initiation of decreased potassium circulating levels with hypothermia supports the thesis of temperature sensitive cell membrane potassium channels affecting extracellular to intracellular shifts of potassium. Results of this study indicate that renal potassium regulation is maintained in hypothermia and functions to decrease urinary potassium loss in the face of hypokalemia. The views expressed are those of the authors and do not necessarily reflect the offcial policy or position of the Defense Health Agency, Department of the Army, Department of Defense, or the U.S. Government. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Role of local vasoconstrictors in diving performance of two pinniped species

Diving mammals extend submergence time through bradycardia and reduced peripheral perfusion to certain tissues. Thus, local blood flow regulation under hypoxia may be an essential physiological strategy that fine-tunes metabolic expenditures during breath-hold. We focused on a potent local vasoconstrictor, Endothelin-1 (ET1) and its receptors ETR-A and ETR-B, to determine their potential role in mammalian diving. We hypothesized that less perfused organs (kidney) would have higher signatures of local vasoconstriction (i.e. higher ET1 and receptors), compared to organs known to have higher relative perfusion underwater (heart/left ventricle). Additionally, we compared pinniped species with higher (Weddell seal) and lower (California sea lion) relative dive capabilities. Differences in mRNA expression of vasoconstrictive elements were assessed by 2-way ANOVA to compare tissue and species. In adult animals (n=7 both species) there were significant differences in expression of ET1 between species (F1,16=9.2, p=0.08) and tissues (F1,16=18.4, p=0.0006), with sea lions having consistently higher levels of ET1. ET1 expression was highest in the kidney, with sea lion kidney expressing 25x more ET1 mRNA than heart (posthoc p=0.0007). The expression ratio of ET A and B receptors also differed across tissue (F1,16=19.83 p=0.0004) with B/A highest in the kidney in both species. This is counter to expectations that submergence capability would relate to vasoconstriction potential across species, but supports the hypothesis that within a species, the less-perfused kidney should demonstrate higher potential for local vasoconstriction compared to the heart. Relative expression of ET receptors between tissues also runs counter to our hypothesis. In both divers, the heart expresses relatively more ETR-A, which has a critical role in vasoconstrictive signaling. On the other hand, ETR-B can signal for either vasoconstriction or vasodilation depending on its location within the endothelium or smooth muscle. Kidney in both species expresses relatively more ETR-B, indicating potential for nuanced vasoregulatory control through the endothelin pathway in this tissue. Receptor localization will be determined by immuno-staining to investigate functional differences between tissues. We also investigated the development of diving by comparing the same biomarkers in adults versus pups (n=10 seals, n=3 sea lions) using a separate 2-way ANOVA for each species. We expected that signatures of vasoregulatory potential would be less evident in the novice diving pups. Concordantly, ET1 is lower in sea lion pups than adults (F1,12=5.097, p=0.043); ET1 mRNA is 23x lower in the pup kidney compared to adult (posthoc p=0.02). Receptor expression followed the same patterns in both species, with the highest expression of ETR-A noted in the pup heart, indicating high vasoconstrictive potential in pups, but through tissue specific mechanisms. These results point to differences in the control of local vasoconstriction that occur with development and highlight the physiological components essential to the development of diving. Funding by NSF #2020706. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Abstract 1124: Sympathetic Denervation Models In Murine Femoral Arteries: Acute To Chronic Effects Of 6-hydroxydopamine

Introduction: The autonomic nervous system (ANS) drives blood flow regulation in peripheral arteries. This study aims to develop novel models of sympathetic denervation in peripheral arteries and to characterize subsequent vascular remodeling. We hypothesize that sympathetic denervation of murine femoral arteries can be achieved through local administration of neurotoxin 6-hydroxydopamine (6-OHDA). Methods: BALB/c mice underwent local administration of 6-OHDA to the left femoral artery, while the contralateral artery received vehicle solution. Two approaches were tested: (1) Acute: a one-time topical application following surgical exposure of femoral arteries (N=8, male, Fig. A ), and (2) Chronic: weekly subcutaneous injections near the femoral arteries (N=11, male and female, Fig. B ). Hindlimb perfusion was assessed with laser Doppler imaging, and arterial structure and remodeling were evaluated with histology and immunohistochemistry at one, two, or four weeks. Results: One-time 6-OHDA application (Acute) led to temporary femoral artery denervation (reduction in tyrosine hydroxylase) for one week ( Fig. C – D ), with inflammation observed in both 6-OHDA and vehicle-treated arteries. No vascular wall remodeling was observed after temporary denervation. Weekly subcutaneous 6-OHDA injections (Chronic) resulted in persistent denervation throughout the four-week period in male mice, while female mice displayed variable outcomes ( Fig. E – F ). Sustained sympathetic denervation in the chronic model led to reduced hindlimb blood perfusion at low core temperatures ( Fig. G – H ), though no significant differences were detected in vascular smooth muscle cell phenotype or extracellular matrix composition. Conclusions: Local administration of 6-OHDA is an effective means of peripheral artery sympathetic denervation with controllable duration. This innovative approach of targeting the ANS unveils new prospects for advancing vascular therapies.

Impact of Peripheral Versus Central Insulin on Cerebrovascular Compliance in Healthy Young Adults

Objective: Vascular compliance is an essential component of cerebral blood flow regulation. Prior work has shown cerebral vasodilation (elicited by hypercapnia) reduces cerebrovascular compliance (Ci); however, this work has yet to be translated to other vasoactive compounds. Insulin has important vasodilatory effects in the peripheral circulation, but less is known about the role of insulin in cerebrovascular control. Herein, we hypothesized both peripheral (intravenous) and central (intranasal) insulin administration would increase indices of cerebral blood flow and reduce Ci in healthy young adults. Methods: Twenty-five healthy young adults (8 female; 26±7 yrs, 25±3 kg/m2) were assigned to two separate protocols (NCT05244694, NCT05153395). Middle cerebral artery blood velocity (MCAv, transcranial Doppler ultrasound) was measured at baseline and under two study conditions: 1) at the end of a 60 min hyperinsulinemic euglycemic infusion, and 2) 60 min following 160 IU of intranasal insulin. Indices of Ci were calculated using a modified Windkessel model applied to blood pressure (finger photoplethysmography) and corresponding MCAv waveforms collected over a 5-min period (10 waveforms) at baseline and during the aforementioned insulin conditions. Results: Blood glucose remained unchanged throughout both protocols (both p>0.05). MCAv was maintained over time under both insulin conditions (protocol 1: 60±13 to 62±17 cm/s, p=0.635; protocol 2: 58±9 to 53±14 cm/s, p=0.146). In contrast, Ci decreased (0.00028±0.00010 to 0.00021±0.00007 cm/s/mmHg, p=0.010) from baseline during peripheral (intravenous) insulin administration. No change in Ci (0.00049±0.00025 to 0.00040±0.00018 cm/s/mmHg, p=0.189) were observed following intranasal insulin administration. Conclusions: Contrary to our hypothesis, there was no effect of peripheral or central insulin administration on resting MCAv in healthy young adults. However, intravenous (but not intranasal) insulin reduced Ci by approximately 25% from baseline values. These findings advance our understanding of cerebrovascular control mechanisms during insulin exposure and provide the opportunity to extend this work to diseased states characterized by insulin resistance, including diabetes. CAFNR Joy of Discovery (JKL, JP). This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Microvascular development and remodeling

Skeletal fragility is an important complication of Type 1 Diabetes (T1D), particularly among older adults. Microvascular disease (MVD) has been linked to worse bone health in T1D, suggesting a potential direct pathophysiologic link between vascular disease and bone deficits. However, bone vascular control has not been explored in the context of T1D. Thus, this preliminary work investigates key mechanisms of regulation of the bone vasculature in older adults with T1D. Myogenic vasoconstriction and reactive hyperemia of tibial blood flow were assessed in older healthy adults (n=9, 65 ± 7 yrs) and older adults with T1D (n=10, 63 ± 6 yrs). Myogenic vasoconstriction was assessed in response to leg dependency (two levels of increased arterial transmural pressure obtained by lowering the leg below heart level) and reactive hyperemia was assessed in response to lower leg arterial occlusion via thigh cuff inflation. The initial peak reactive hyperemic response was considered a surrogate of myogenic vasodilation. For both stimuli, tibial blood flow was assessed via NIRS as total hemoglobin (tHb) and whole leg blood flow velocity (LBF) in the popliteal artery of the same leg was measured via Doppler ultrasound. Data are presented as mean±standard error. In response to leg dependency, with increased perfusion pressure, older adults had a tendency for smaller declines in LBF (L1: -3.85 ± 2.01 cm/s; L2: -6.22 ± 4.19 cm/s) compared to older adults with T1D (L1: -6.14 ±2.24 cm/s; L2: -10.4 ± 1.90 cm/s; group p=0.06, level p=0.07). Tibial tHb did not decline in older adults (L1: 1.16 ± 7.27 M; L2: 9.11 ± 13.8 M), but decreased progressively in those with T1D (L1: - 3.40 ± 2.79 M, L2: -6.14 ± 2.24 M, group p<0.01, group*level p=0.07), indicating pronounced tibial myogenic vasoconstriction. In response to reactive hyperemia, LBF increased rapidly with cuff release in both groups (older adults: 50.8 ±22.7cm/s; T1D: 40.0 ± 13.4cm/s). Despite similar responses in LBF, tibial tHb surpassed baseline values in older adults (1.50 ± 5.35M), whereas tibial tHb did not reach baseline values within 5 min post cuff release in T1D (-2.85 ± 5.09M, p=0.09), indicating impaired tibial myogenic vasodilation. Interestingly, older adults with T1D and MVD (n=5) had a stronger tendency for greater tibial myogenic vasoconstriction at both levels and significantly impaired reactive hyperemic response compared to those with no MVD (n=5). Our preliminary results indicate that older adults with T1D have greater myogenic vasoconstriction and impaired reactive hyperemic responses that appear to be worse in the presence of MVD. Alterations in myogenic control act to compromise blood flow regulation, restricting blood flow to bone, and potentially contributing to diabetes-inducted skeletal fragility. NIH NIDDK R01 DK124710. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

The role of neuroendothelial cells in aging-related vascular cognitive impairment

Vascular cognitive impairment (VCI) is a growing health problem in many developed countries due to aging of its population. Aging-induced impairment of neurovascular coupling (NVC) responses and brain microvascular rarefaction have been implicated as major driving mechanisms in age-related cognitive decline. One of the cellular hallmarks of NVC involve the release of vasodilator nitric oxide (NO) by endothelial cells in response to mediators released from activated neurons. Recent studies from our group identified and characterized a novel, minority subtype of scattered ECs with endothelial and neuronal characteristics, hence the name neuroendothelial cell (NECs). NECs present a well-defined arteriovenous zonal localization exclusively in small resistance arterioles with the highest density in the brain followed by the kidney. Intravital multiphoton microscopy (MPM) of intact brain arterioles in vivo suggest that NECs play an important role in regulating blood flow to the brain and able to detect changes in systemic blood pressure, hypoxia and perhaps other metabolic changes in the local microenvironment. Our central hypothesis is that NECs are novel key players in blood flow autoregulation, vascular control of organ functions in both short-term (hemodynamics) and long-term (angiogenesis, tissue regeneration). We further hypothesize that the decrease in NEC density and function in aged subjects is a major player in the development of age-related cerebral microvascular pathologies and that augmenting NEC number and function in aged animals will provide therapeutic benefit. This study used a NEC specific comprehensive research toolbox including NEC-GFP transgenic mouse models and high-resolution single-cell based transcriptome analysis to establish the NEC specific molecular atlas in young adult (3 month of age) and aged (2 years of age) animals. Furthermore, transgenic animal models combined with serial intravital imaging of the same tissue volume over consecutive days was used to study changes in vascular endothelial cell composition in response to NEC stimuli in young adult and aged mice. Cell fate tracking studies of the Nos1-lineage combined with Nos1 immunostaining revealed that NECs represent a permanent cell type with terminal neuronal differentiation. Importantly, NEC density is reduced with aging in all organs including the brain. High resolution single-cell based transcriptome analysis of 100K endothelial cells isolated from mouse brain demonstrated that, in contrast to other ECs, NECs highly express several traditional (e.g., Nos1, Angpt1, Egfl8) and novel (e.g., Cytl1, MGP, Gkn3) tissue trophic factors that are known to play important roles in acute hemodynamic responses including NO mediated functional hyperemia, and in chronic settings in angiogenesis, aging, vascular (dys)function, and chronic vascular diseases. Furthermore, the expression of many of these factors were significantly reduced in NECs isolated from aged animals. In conclusion, the newly discovered NEC-specific molecular and signaling mechanisms may play a role in the age-related decrease in NVC capacity and microvascular rarefaction and may be targeted for therapeutic benefits in age related VCI. American Society of Nephrology Carl W. Gottschalk Research Scholar Grant. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Is functional MRI meaningful in migraine?

Functional magnetic resonance imaging (fMRI) is an imaging method that enables us to understand brain anatomy, mapping and its function. While fMRI was previously used in experimental studies, it has now been used in clinical studies. Imaging in fMRI is based on measuring the increase in regional blood flow caused by cortical activation. fMRI indirectly demonstrates neural activation by detecting increases in oxygenation. fMRI relies on the sensitivity of magnetic resonance signals to changes in deoxyhemoglobin levels or perfusion, reflecting the metabolic and hemodynamic responses associated with neural activation. Imaging is arranged in the clinic for primary headaches if needed for a differential diagnosis. However, imaging studies are utilized in scientific research to elucidate the pathophysiology. Migraine is a common episodic disorder characterized by recurring attacks. Investigating the functional structure of the brain during both attack and interictal periods is crucial in understanding migraine pathology. However, capturing patients' migraine attacks for monitoring purposes without treatment is considered unethical in many countries. Moreover, conducting such studies is hindered by the requirement for prolonged hospital stays and extended imaging times, which significantly increase costs. Despite the challenges of conducting research in migraine patients, fMRI stands out as an excellent imaging method for investigating the functional brain structures involved in this episodic disorder. Several fMRI studies have yielded valuable insights into the pathophysiology of migraine. fMRI is believed to offer valuable guidance in refining our understanding of migraine-specific mechanisms, facilitating biomarker studies for migraine activity, and elucidating abnormal functions in regions affected by migraine. Monitoring treatment response using biomarkers is anticipated to be an effective tool for identifying targets for migraine treatment, including assessing treatment efficacy in the development of new migraine-specific therapies.

Cerebral blood flow regulation in hypobaric hypoxia: role of haemoconcentration.

During acute hypoxic exposure, cerebral blood flow (CBF) increases to compensate for the reduced arterial oxygen content (CaO2). Nevertheless, as exposure extends, both CaO2 and CBF progressively normalize. Haemoconcentration is the primary mechanism underlying the CaO2 restoration and may therefore explain, at least in part, the CBF normalization. Accordingly, we tested the hypothesis that reversing the haemoconcentration associated with extended hypoxic exposure returns CBF towards the values observed in acute hypoxia. Twenty-three healthy lowlanders (12 females) completed two identical 4-day sojourns in a hypobaric chamber, one in normoxia (NX) and one in hypobaric hypoxia (HH, 3500m). CBF was measured by ultrasound after 1, 6, 12, 48 and 96h and compared between sojourns to assess the time course of changes in CBF. In addition, CBF was measured at the end of the HH sojourn after hypervolaemic haemodilution. Compared with NX, CBF was increased in HH after 1h (P=0.001) but similar at all later time points (all P>0.199). Haemoglobin concentration was higher in HH than NX from 12h to 96h (all P<0.001). While haemodilution reduced haemoglobin concentration from 14.8 ± 1.0 to 13.9 ± 1.2g·dl-1 (P<0.001), it did not increase CBF (974 ± 282 to 872 ± 200ml·min-1; P=0.135). We thus conclude that, at least at this moderate altitude, haemoconcentration is not the primary mechanism underlying CBF normalization with acclimatization. These data ostensibly reflect the fact that CBF regulation at high altitude is a complex process that integrates physiological variables beyond CaO2. KEY POINTS: Acute hypoxia causes an increase in cerebral blood flow (CBF). However, as exposure extends, CBF progressively normalizes. We investigated whether hypoxia-induced haemoconcentration contributes to the normalization of CBF during extended hypoxia. Following 4 days of hypobaric hypoxic exposure (corresponding to 3500m altitude), we measured CBF before and after abolishing hypoxia-induced haemoconcentration by hypervolaemic haemodilution. Contrary to our hypothesis, the haemodilution did not increase CBF in hypoxia. Our findings do not support haemoconcentration as a stimulus for the CBF normalization during extended hypoxia.

Signalling switches maintain intercellular communication in the vascular endothelium.

The single layer of cells lining all blood vessels, the endothelium, is a sophisticated signal co-ordination centre that controls a wide range of vascular functions including the regulation of blood pressure and blood flow. To co-ordinate activities, communication among cells is required for tissue level responses to emerge. While a significant form of communication occurs by the propagation of signals between cells, the mechanism of propagation in the intact endothelium is unresolved. Precision signal generation and targeted cellular manipulation was used in conjunction with high spatiotemporal mesoscale Ca2+ imaging in the endothelium of intact blood vessels. Multiple mechanisms maintain communication so that Ca2+ wave propagation occurs irrespective of the status of connectivity among cells. Between adjoining cells, regenerative IP3-induced IP3 production transmits Ca2+ signals and explains the propagated vasodilation that underlies the increased blood flow accompanying tissue activity. The inositide is itself sufficient to evoke regenerative phospholipase C-dependent Ca2+ waves across coupled cells. None of gap junctions, Ca2+ diffusion or the release of extracellular messengers is required to support this type of intercellular Ca2+ signalling. In contrast, when discontinuities exist between cells, ATP released as a diffusible extracellular messenger transmits Ca2+ signals across the discontinuity and drives propagated vasodilation. These results show that signalling switches underlie endothelial cell-to-cell signal transmission and reveal how communication is maintained in the face of endothelial damage. The findings provide a new framework for understanding wave propagation and cell signalling in the endothelium.

Portal Hemodynamics in Liver Resection and Transplantation.

The hepatic blood supply and its several homeostatic and pathologic processes has always been a matter of great interest. Many views commonly held today are derived from an earlier era, but major reorientations have occurred recently in almost all aspects of knowledge of the role and regulation of hepatic blood flow. Moreover, with the advent of liver transplantation (LT), especially living donor LT (LDLT) there has been a resurgence of interest in attempting to comprehend this deceptively simple topic. It is nonetheless important to concede that even though our knowledge on the practical modulation of hepatic hemodynamics has expanded enormously, there still remain the need to explore the depths of our remaining ignorance to further improve outcomes in LDLT. This review focuses on the current view, controversies and gaps in knowledge of the hepatic vascular bed, with an emphasis on the importance of portal hemodynamics in liver disease and its impact on liver regeneration and LT.

Surgical outcomes of the systemic-to-pulmonary artery shunt: risk factors of post-operative acute events and effectiveness of regulation of pulmonary blood flow with metal clips.

The aim of this study was to analyze the risk factors for acute events after systemic-to-pulmonary shunt (SPS) and to investigate the effectiveness of pulmonary blood flow regulation with a metal clip. The case histories of 116 patients (78 biventricular [BV] and 38 single ventricle [SV] physiology) who underwent SPS between 2010 and 2021 were retrospectively reviewed. Our strategy was to delay SPS until 1month of age; pulmonary blood flow (PBF) regulation by partial clipping of the graft, if needed. Cases of aortic cross-clamping were excluded from this study. CPB was used in 49 (42%) patients: the median age at SPS was 1month (2days to 16years), and the sternotomy approach in 65. Discharge survival was 98.3% (114/116); hospital death occurred in 1.7% due to coronary ischemia. Inter-stage mortality occurred in 1.7% (shunt thrombosis, 1; pneumonia, 1). Pre-discharge acute events occurred in 7 patients (6.0%): thrombosis 3, pulmonary over-circulation 2, and coronary ischemia 2. Multiple logistic regression analysis revealed that pulmonary atresia with intact ventricular septum (PA/IVS) (p = 0.0253) was an independent risk factor for acute events. Partial clipping of the graft was performed in 24 patients (pulmonary atresia 15) and clip removal was performed by catheter intervention in 9 patients; no coronary ischemic events and graft injury occurred in these patients. Surgical outcomes after SPS were acceptable and metal clip regulation of pulmonary blood flow appears to be safe and effective. PA/IVS was still a significant risk factor for acute events.

A constrained constructive optimization model of branching arteriolar networks in rat skeletal muscle.

Blood flow regulation within the microvasculature reflects a complex interaction of regulatory mechanisms and varies spatially and temporally according to conditions such as metabolism, growth, injury, and disease. Understanding the role of microvascular flow distributions across conditions is of interest to investigators spanning multiple disciplines; however, data collection within networks can be labor-intensive and challenging due to limited resolution. To overcome these experimental challenges, computational network models that can accurately simulate vascular behavior are highly beneficial. Constrained constructive optimization (CCO) is a commonly used algorithm for vascular simulation, particularly well known for its adaptability toward vascular modeling across tissues. The present work demonstrates an implementation of CCO aimed to simulate a branching arteriolar microvasculature in healthy skeletal muscle, validated against literature including comprehensive rat gluteus maximus vasculature datasets, and reviews a list of user-specified adjustable model parameters to understand how their variability affects the simulated networks. Network geometric properties, including mean element diameters, lengths, and numbers of bifurcations per order, Horton's law ratios, and fractal dimension, demonstrate good validation once model parameters are adjusted to experimental data. This model successfully demonstrates hemodynamic properties such as Murray's law and the network Fahraeus effect. Application of centrifugal and Strahler ordering schemes results in divergent descriptions of identical simulated networks. This work introduces a novel CCO-based model focused on generating branching skeletal muscle microvascular arteriolar networks based on adjustable model parameters, thus making it a valuable tool for investigations into skeletal muscle microvascular structure and tissue perfusion.NEW & NOTEWORTHY The present work introduces a CCO-based algorithm for generating branching arteriolar networks, with adjustable model parameters to enable modeling in varying skeletal muscle tissues. The geometric and hemodynamic parameters of the generated networks have been comprehensively validated using experimental data collected previously in-house and from literature. This is one of few validated CCO-based models to specialize in skeletal muscle microvasculature and acts as a beneficial tool for investigating the microvasculature for hypothesis testing and validation.

Non-contrast preoperative MRI for determining renal perfusion and visualizing renal arteries in potential living kidney donors at 1.5 Tesla.

The aim of this work was to create and evaluate a preoperative non-contrast-enhanced (CE) magnetic resonance imaging (MRI)/angiography (MRA) protocol to assess renal function and visualize renal arteries and any abnormalities in potential living kidney donors. In total, 28 subjects were examined using scintigraphy to determine renal function. In addition, 3D-pseudocontinuous arterial spin labeling (pCASL), a 2D-non-CE electrocardiogram-triggered radial quiescent interval slice-selective (QISS-MRA), and 4D-CE time-resolved angiography with interleaved stochastic trajectories (CE-MRA) were performed to assess renal perfusion, visualize renal arteries and detect any abnormalities. Two glomerular filtration rates [described by Gates (GFRG) and according to the Chronic Kidney Disease Epidemiology Collaboration formula (GFRCKD-EPI)]. The renal volumes were determined using both MRA techniques. The mean value of regional renal blood flow (rRBF) on the right side was significantly higher than that on the left. The agreements between QISS-MRA and CE-MRA concerning the assessment of absence or presence of an aberrant artery and renal arterial stenosis were perfect. The mean renal volumes measured in the right kidney with QISS-MRA were lower than the corresponding values of CE-MRA. In contrast, the mean renal volumes measured in the left kidney with both MRA techniques were similar. The correlation between the GFRG and rRBF was compared in the same manner as that between GFRCKD-EPI and rRBF. The combination of pCASL and QISS-MRA constitute a reliable preoperative protocol with a total measurement time of <10min without the potential side effects of gadolinium-based contrast agents or radiation exposure.

Herpesvirus Infection of Endothelial Cells as a Systemic Pathological Axis in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome.

Understanding the pathophysiology of myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is critical for advancing treatment options. This review explores the novel hypothesis that a herpesvirus infection of endothelial cells (ECs) may underlie ME/CFS symptomatology. We review evidence linking herpesviruses to persistent EC infection and the implications for endothelial dysfunction, encompassing blood flow regulation, coagulation, and cognitive impairment-symptoms consistent with ME/CFS and Long COVID. This paper provides a synthesis of current research on herpesvirus latency and reactivation, detailing the impact on ECs and subsequent systemic complications, including latent modulation and long-term maladaptation. We suggest that the chronicity of ME/CFS symptoms and the multisystemic nature of the disease may be partly attributable to herpesvirus-induced endothelial maladaptation. Our conclusions underscore the necessity for further investigation into the prevalence and load of herpesvirus infection within the ECs of ME/CFS patients. This review offers conceptual advances by proposing an endothelial infection model as a systemic mechanism contributing to ME/CFS, steering future research toward potentially unexplored avenues in understanding and treating this complex syndrome.

The Importance of Intra-Islet Communication in the Function and Plasticity of the Islets of Langerhans during Health and Diabetes.

Islets of Langerhans are anatomically dispersed within the pancreas and exhibit regulatory coordination between islets in response to nutritional and inflammatory stimuli. However, within individual islets, there is also multi-faceted coordination of function between individual beta-cells, and between beta-cells and other endocrine and vascular cell types. This is mediated partly through circulatory feedback of the major secreted hormones, insulin and glucagon, but also by autocrine and paracrine actions within the islet by a range of other secreted products, including somatostatin, urocortin 3, serotonin, glucagon-like peptide-1, acetylcholine, and ghrelin. Their availability can be modulated within the islet by pericyte-mediated regulation of microvascular blood flow. Within the islet, both endocrine progenitor cells and the ability of endocrine cells to trans-differentiate between phenotypes can alter endocrine cell mass to adapt to changed metabolic circumstances, regulated by the within-islet trophic environment. Optimal islet function is precariously balanced due to the high metabolic rate required by beta-cells to synthesize and secrete insulin, and they are susceptible to oxidative and endoplasmic reticular stress in the face of high metabolic demand. Resulting changes in paracrine dynamics within the islets can contribute to the emergence of Types 1, 2 and gestational diabetes.

WNK kinase is a vasoactive chloride sensor in endothelial cells

Endothelial cells (ECs) line the wall of blood vessels and regulate arterial contractility to tune regional organ blood flow and systemic pressure. Chloride (Cl-) is the most abundant anion in ECs and the Cl- sensitive With-No-Lysine (WNK) kinase is expressed in this cell type. Whether intracellular Cl- signaling and WNK kinase regulate EC function to alter arterial contractility is unclear. Here, we tested the hypothesis that intracellular Cl- signaling in ECs regulates arterial contractility and examined the signaling mechanisms involved, including the participation of WNK kinase. Our data obtained using two-photon microscopy and cell-specific inducible knockout mice indicated that acetylcholine, a prototypical vasodilator, stimulated a rapid reduction in intracellular Cl- concentration ([Cl-]i) due to the activation of TMEM16A, a Cl- channel, in ECs of resistance-size arteries. TMEM16A channel-mediated Cl- signaling activated WNK kinase, which phosphorylated its substrate proteins SPAK and OSR1 in ECs. OSR1 potentiated transient receptor potential vanilloid 4 (TRPV4) currents in a kinase-dependent manner and required a conserved binding motif located in the channel C terminus. Intracellular Ca2+ signaling was measured in four dimensions in ECs using a high-speed lightsheet microscope. WNK kinase-dependent activation of TRPV4 channels increased local intracellular Ca2+ signaling in ECs and produced vasodilation. In summary, we show that TMEM16A channel activation reduces [Cl-]i, which activates WNK kinase in ECs. WNK kinase phosphorylates OSR1 which then stimulates TRPV4 channels to produce vasodilation. Thus, TMEM16A channels regulate intracellular Cl- signaling and WNK kinase activity in ECs to control arterial contractility.

Interactions between Beta-Amyloid and Pericytes in Alzheimer's Disease.

Alzheimer's disease (AD) is an age-related progressive neurodegenerative disorder characterized by aberrant amyloid precursor protein (APP) cleavage, pathological aggregations of beta-amyloid (Aβ) that make up Aβ plaques and hyperphosphorylation of Tau that makes up neurofibrillary tangles (NFTs). Although progress has been made in research on AD, the fundamental causes of this disease have not been fully elucidated. Recent studies have shown that vascular dysfunction especially the loss of pericytes plays a significant role in the onset of AD. Pericytes play a variety of important roles in the nervous system including the regulation of the cerebral blood flow (CBF), the formation and maintenance of the blood-brain barrier (BBB), angiogenesis, and the clearance of toxic substances from the brain. Pericytes participate in the transport of Aβ through various receptors, and Aβ acts on pericytes to cause them to constrict, detach, and die. The loss of pericytes elevates the levels of Aβ1-40 and Aβ1-42 by disrupting the integrity of the BBB and reducing the clearance of soluble Aβ from the brain interstitial fluid. The aggravated deposition of Aβ further exacerbates pericyte dysfunction, forming a vicious cycle. The combined influence of these factors eventually results in the loss of neurons and cognitive decline. Further exploration of the interactions between pericytes and Aβ is beneficial for understanding AD and could lead to the identification of new therapeutic targets for the prevention and treatment of AD. In this review, we explore the characterization of pericytes, interactions between pericytes and other cells in the neurovascular unit (NVU), and the physiological functions of pericytes and dysfunctions in AD. This review discusses the interactions between pericytes and Aβ, as well as current and further strategies for preventing or treating AD targeting pericytes.

Stealing-like phenomenon with interscalene nerve block and its influence on the regional blood flow during shoulder arthroscopic surgery

Background Hypotensive anesthesia during shoulder arthroscopy is mandatory. Hypotension in the supine or decubitus position is safe and effective for reducing blood losses and for maintaining a clear surgical field. However, in the beach chair position, major complications have been reported. The current study claims that the alignment of the vessel in these regions favor a stealing-like phenomenon associated with interscalene block. This phenomenon has a good impact on the surgical field. Results There was a significant change in the peak systolic velocity between the two populations with values of 57±5 in group I versus 90±12 in group G, with a clearer surgical field in group I than in group G. The need for the intraoperative adjuvant analgesics was higher in group G (29 patients) compared with group I (10 patients) as was the pain score at early postoperative intervals of 6 and 12 h. Conclusion The distribution of blood vessels in this region favors a stealing-like phenomenon may be because of the associated vasoplegic effect with the interscalene nerve block, yielding a favorable surgical field without deliberate hypotension.

342 Impact of the Endothelial Nucleotidase on Thrombosis

OBJECTIVES/GOALS: Contrary to current dogma, prior work has suggested that in humans, SNP-determined endothelial cell reduction in CD39 expression associates with a diminished risk for venous thromboembolism. Our objective was to examine the impact of endothelial cell (EC) CD39 expression on arterial thrombosis that replicates human data. METHODS/STUDY POPULATION: We generated a novel CD39 cell-specific conditional knockout mouse line for endothelial cells (EC-cKO: Tie2-Cre+; cd39flox/flox versus WT: Tie2-Cre-; cd39flox/flox). We validated the knockout of expression of CD39 on EC using FACS analysis and measured EC CD39 activity using the Kinase Glo ATP hydrolysis assay on magnetically sorted EC. We then used a standard FeCl3 carotid injury model to evaluate time to arterial thrombosis in vivo by measuring time to occlusion tracked via a Doppler flow probe on the exposed vessel. RESULTS/ANTICIPATED RESULTS: FACS analysis revealed a specific 97% knockout of CD39 expression on EC (p&lt;0.001) but not on other cells within the vasculature. There was also significant reduction in ATP hydrolysis (81%; p=0.019) in EC-cKO mouse EC versus WT. We next examined the time to arterial thrombosis. EC-specific conditional knockout of CD39 exhibited a significant prolongation in time to thrombosis compared to WT (WT: 8.28 minutes +/- 0.82; EC-cKO: 11.92 minutes +/- 1.34; p=0.024). Analysis of carotid blood-flow revealed that EC-cKO and WT mice had similar baseline blood flow velocity (p=0.51), but after vessel injury with FeCl3, EC-cKO mice exhibited a 16% increase maximal flow velocity relative to baseline compared to WT (p&lt;0.001), as well as a 19% increase at 2-minutes post-injury in comparison to EC-WT mice (p&lt;0.001). DISCUSSION/SIGNIFICANCE: Our findings demonstrate that CD39 activity plays a role in modulating arterial thrombosis and blood-flow regulation within the vasculature. These findings exemplify the therapeutic potential of modulating endothelial CD39 activity, as well as the potential for using SNPs within the gene coding for CD39 as a cardiovascular disease marker.

Glaucoma Patient with Suspected Flammer Syndrome: Diagnostic Procedures and Therapeutic Implications

If glaucoma damage develops despite normal intraocular pressure or if the damage progresses despite well-controlled intraocular pressure, we usually find other risk factors. One important group are the vascular factors. We should focus not only on the classical risk factors of atherosclerosis, such as arterial hypertension or dyslipidaemia, but also on dysregulation of blood flow, especially on primary vascular dysregulation (PVD). Low blood pressure, either current or in adolescence, low body mass index or frequently cold hands and feet may provide important hints. Very often PVD is coupled with a number of other symptoms and signs, and we then speak of a Flammer Syndrome (FS). If there is any indication of FS, we take a targeted patient history, undertake 24 h blood pressure monitoring, measure retinal venous pressure, and perform a dynamic retinal vessel analysis or nail fold capillary microscopy. This is especially recommended if the patient is relatively young or the damage is progressing rapidly. If the suspicion is confirmed, we then try to reduce the drops in blood pressure, lower the retinal venous pressure, improve the regulation of blood flow and reduce the oxidative stress in the mitochondria.