Red Blood Cell Flux Research Articles

Abstract 46: Reduced Angiotensin II Type 2 Receptor-Mediated Responses Contribute to Increased Angiotensin II Vasoconstrictor Sensitivity in Otherwise Healthy Women With a History Of Preeclampsia

Women with a history of preeclampsia (hxPE) have a ≥4-fold risk for developing cardiovascular disease compared to matched women who had a healthy pregnancy (hxHC). Angiotensin (ang) II-mediated vasoconstriction contributes to the persistently reduced microvascular function in the years after preeclampsia. Excessive activation of ang II type 1 receptors (AT 1 R) is one putative mechanism underlying increased ang II constrictor sensitivity. This may be countered by ang II type 2 receptor (AT 2 R) activation; however, the extent that reductions in AT 2 R-mediated responses contribute to increased ang II sensitivity after preeclampsia is unknown. Using the cutaneous microcirculation as a model, we hypothesized that 1) AT 2 R-mediated dilation is attenuated in hxPE compared with hxHC, 2) AT 1 R inhibition improves reduced AT 2 R-mediated dilation in hxPE, and 3) AT 2 R inhibition would increase ang II-mediated constriction in hxHC but have no effect in hxPE. Nine hxPE (37±5 years) and 9 matched hxHC (34±5 years) within 5 years postpartum had 4 intradermal microdialysis fibers placed in the ventral forearm for the local delivery of pharmacological agents. Two fibers received graded infusions of compound 21 (AT 2 R agonist; 10 -14 -10 -8 mol/L) alone or co-perfused with losartan (AT 1 R antagonist; 43µmol/L) for the assessment of AT 2 R-mediated dilation. The remaining 2 sites received graded infusions of ang II (10 −20 –10 −4 mol/L) alone or co-perfused with PD-123319 (AT 2 R antagonist; 1µmol/L) to assess the role of AT 2 R in vasoconstrictor sensitivity to ang II. Red blood cell flux was measured directly over each fiber and cutaneous vascular conductance was calculated (CVC=flux/MAP) and expressed as a % maximum (43°C + 28mM SNP) or % baseline. Those with hxPE had attenuated AT 2 R-mediated dilation (hxPE: 15±5 vs hxHC: 27±9%max; P=0.01) that was improved with AT 1 R inhibition (losartan: 22±7 vs control: 15±5%max; P=0.003). Vasoconstrictor sensitivity to ang II was greater in hxPE compared with hxHC (hxPE: 39±14 vs hxHC: 55±6%baseline; P<0.001). AT 2 R inhibition increased the vasoconstrictor response to ang II in hxHC (PD-123319: 39±12 vs control: 55±65%baseline; P<0.001) but had no effect in hxPE (PD-123319: 39±13 vs control: 39±14%baseline; P=0.29). These data suggest that women with a history of preeclampsia have reductions in AT 2 R-mediated dilation that contributes to increased ang II vasoconstrictor sensitivity and sustained microvascular dysfunction after preeclampsia.

The role of the heart in the evolution of aerobic performance.

Aerobic metabolism underlies vital traits such as locomotion and thermogenesis, and aerobic capacity influences fitness in many animals. The heart is a key determinant of aerobic capacity, but the relative influence of cardiac output versus other steps in the O2 transport pathway remains contentious. In this Commentary, we consider this issue by examining the mechanistic basis for adaptive increases in aerobic capacity (thermogenic V̇O2,max; also called summit metabolism) in deer mice (Peromyscus maniculatus) native to high altitude. Thermogenic V̇O2,max is increased by acclimation to cold hypoxia (simulating high-altitude conditions), and high-altitude populations generally have greater V̇O2,max than their low-altitude counterparts. This plastic and evolved variation in V̇O2,max is associated with corresponding variation in maximal cardiac output, along with variation in other traits across the O2 pathway (e.g. arterial O2 saturation, blood haemoglobin content and O2 affinity, tissue O2 extraction, tissue oxidative capacity). By applying fundamental principles of gas exchange, we show that the relative influence of cardiac output on V̇O2,max depends on the O2 diffusing capacity of thermogenic tissues (skeletal muscles and brown adipose tissues). Functional interactions between cardiac output and blood haemoglobin content determine circulatory O2 delivery and thus affect V̇O2,max, particularly in high-altitude environments where erythropoiesis can increase haematocrit and blood viscosity. There may also be functional linkages between cardiac output and tissue O2 diffusion due to the role of blood flow in determining capillary haematocrit and red blood cell flux. Therefore, the functional interactions between cardiac output and other traits in the O2 pathway underlie the adaptive evolution of aerobic capacities.

Dietary NO3− does not enhance endothelial dependent cutaneous vascular conductance in older women

Prior work has yet to determine whether the reduction of dietary nitrate (NO3−) to NO, via the enterosalivary pathway, may modify cutaneous vascular conductance (CVC) responses to local heating in older women. Changes occurring with the transition to menopause related to hormonal flux, increased adiposity, and/or decreased physical activity may further compound the negative influence of aging on nitric oxide (NO)-dependent CVC. Herein, we characterized changes in NO-dependent CVC following acute ingestion of 140 mL of NO3−-rich beetroot juice in 24 older women (age: 65 ± 5 y, BMI: 31.2 ± 3.7 kg/m2). Red blood cell (RBC) flux was measured continuously via laser-Doppler flowmetry on the dorsal aspect of the forearm during local skin heating to 39 °C/44 °C before and 3 h after NO3− ingestion. NO-dependent changes in CVC were calculated as RBC flux/mean arterial blood pressure at 39 °C and normalized as a proportion of maximal CVC at 44 °C (%CVCmax). Changes (Δ) in fractional exhaled NO (FeNO) following NO3− ingestion were used an index of NO bioavailability. Despite increased FeNO (+81 ± 70 %, P < 0.001), %CVCmax at 39 °C was reduced (−16 ± 10 %, P < 0.001) following NO3− ingestion. A greater reduction in %CVCmax was weakly to moderately associated with higher body fat% (r = 0.45 [0.05–0.72], P = 0.029), central adiposity% (r = 0.50 [0.13–0.75], P = 0.012), neutrophil% (r = 0.42 [0.02–0.70], P = 0.041), and higher neutrophil to lymphocyte ratio (r = 0.49 [0.11–0.75], P = 0.016). These findings demonstrate a single dose of dietary NO3− does not promote CVC responses to local heating in sedentary older women with overweight and obesity. Correlation with multiple biomarkers suggest systemic inflammation may be involved.

An-Gong-Niu-Huang-Wan (AGNHW) regulates cerebral blood flow by improving hypoperfusion, cerebrovascular reactivity and microcirculation disturbances after stroke

BackgroundThe restoration of cerebrovascular regulation and improvement of cerebral blood flow in ischaemic regions are crucial for improving the clinical prognosis after stroke. An-Gong-Niu-Huang-Wan (AGNHW) is a famous traditional compound Chinese medicine that has been used for over 220 years to treat acute ischaemic stroke; however, its role in the regulation of cerebral blood flow is still unclear. The aim of the present study was to investigate the regulatory effect of AGNHW on cerebral blood flow and microcirculation after ischaemic stroke and to elucidate the underlying mechanisms involved.MethodsMale C57BL/6 mice were subjected to distal middle cerebral artery occlusion (dMCAO) and randomly assigned to the sham, MCAO, or AGNHW groups. AGNHW was administered intragastrically 1 h after dMCAO. The rotarod test was utilized to evaluate behavioural function; TTC was used to determine the infarct volume; and ischaemic injury was assessed by detecting brain levels of SOD, MDA and NO. Then, cortical perfusion and acetazolamide-induced cerebrovascular reactivity were assessed using laser speckle contrast imaging, and the velocity and flux of red blood cells in cortical capillaries were detected using two-photon laser scanning microscopy. In addition, we employed RNA-Seq to identify variations in gene expression profiles and assessed endothelium-dependent changes in microcirculatory dysfunction by measuring vasoactive mediator levels.ResultsAGNHW significantly increased cerebral blood flow, reduced the infarct volume, and promoted functional recovery after cerebral ischaemia. AGNHW increased the velocity and flux of red blood cells in capillaries and improved cerebrovascular reactivity in the ischaemic cortex. Furthermore, AGNHW regulated endothelium-dependent microcirculation, as evidenced by decreases in the expression of endothelins (Edn1, Edn3 and Ednrb) and the ratios of brain and serum TXB2/6-keto-PGF1α and ET-1/CGRP.ConclusionsAGNHW improved cerebral hypoperfusion, regulated cerebrovascular reactivity and attenuated microcirculatory dysfunction within the ischaemic cortex after stroke. This outstanding effect was achieved by modulating the expression of genes related to vascular endothelial cell function and regulating endothelium-dependent vasoactive mediators.

Effect of home-based heat therapy on 24-h blood pressure and cutaneous microvascular function in post-menopausal women with hypertension

Hypertension is a leading risk factor for cardiovascular morbidity and mortality and is often accompanied by microvascular dysfunction. Despite a clear effcacy in men, standard antihypertensive medications are less effective in post-menopausal women. Consequently, adjuvant therapies are needed to improve blood pressure control and microvascular function in post-menopausal women. Heat therapy may fill this therapeutic gap as it has been shown to reduce blood pressure and improve microvascular function in healthy and certain clinical populations. Therefore, the purpose of this study was to test the hypothesis that 8 weeks of home-based heat therapy would improve 24-h blood pressure and cutaneous nitric oxide-dependent vasodilation in post-menopausal women with hypertension. Post-menopausal women (69 ± 5 y) with hypertension were randomized to 8 weeks of sham ( N = 15) or heat therapy ( N = 13). Participants immersed their lower legs ~33 cm into a circulated and temperature-controlled (sham: 35 °C; heat therapy: 42 °C) water bath 4 days per week, and 45 min per session. Blood pressure and cutaneous microvascular function and were assessed before (pre) and after (post) the 8-week intervention. Mean arterial blood pressure was measured across 24-h using an ambulatory monitor. To assess microvascular function, an intradermal microdialysis probe was inserted in the anterior aspect of the lower leg at a site directly exposed to water (immersed) and at another site not directly exposed (non-immersed). Red blood cell flux was measured (laser doppler flowmetry) during cutaneous hyperemia induced by 39 °C local heating. N(G)-nitro-L-arginine methyl ester (L-NAME; 20mM) was then infused in each probe until a nadir in red blood cell flux was achieved. Cutaneous vascular conductance was calculated as red blood cell flux divided by mean arterial pressure and normalized to maximal vasodilation (42 °C heating + 56 mM sodium nitroprusside; CVC%max). Nitric oxide-dependent dilation was calculated as the difference between CVC%max measured during the 39 °C plateau and the L-NAME nadir. Mean arterial blood pressure did not differ across time or between groups (sham: pre, 96 ± 5 mmHg vs. post, 96 ± 6 mmHg; heat therapy: pre, 97 ± 4 mmHg vs. 99 ± 7 mmHg; P = 0.5 for interaction). Cutaneous vasodilation induced by local heating did not differ across time for either group (sham: pre, 60 ± 19 CVC%max vs. post, 64 ± 12 CVC%max; heat therapy: pre, 68 ± 15 CVC%max vs. post, 63 ± 13 CVC%max) or between immersed and non-immersed sites ( P = 0.9 for interaction). Similarly, nitric oxide-dependent vasodilation did not differ across time or between sites for either group ( P = 1.0 for interaction). Taken together, 8 weeks of home-based heat therapy does not improve blood pressure or cutaneous microvascular function in post-menopausal women with hypertension. This work was supported by grants from the National Institutes of Health (T32 AG020494; R01AG059314; F32HL167556) and the American Heart Association (TPA958179). 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.

Insulin-Mediated Capillary Recruitment Is Absent in the Cutaneous Microvasculature of Women with a History of Gestational Diabetes Mellitus

Women with a history of gestational diabetes mellitus (GDM) have a significantly greater risk of developing cardiovascular disease and type II diabetes compared to women who had an uncomplicated pregnancy (HC). Although the mechanisms underlying this increased risk are unclear, emerging evidence suggests that microvascular endothelial dysfunction, mediated via reduced nitric oxide (NO)-dependent dilation, persists after pregnancy complicated by GDM. Whether this microvascular dysfunction reduces insulin-mediated responses in these women is unexplored. We hypothesized that insulin-mediated capillary recruitment would be attenuated in women with a history of GDM via NO-dependent mechanisms. 24 women (n=12/group; HC: 35±1 years, 24±4 months post-partum; GDM: 33±1 years, 21±3 months postpartum) underwent intradermal microdialysis, which involved the placement of 2 fibers in the ventral forearm for the local delivery of 10−4M insulin alone or 10−4M insulin+15mM NG-nitro-L-arginine methyl ester (L-NAME, NO-synthase inhibitor). The cutaneous blood flow response to post-occlusive reactive hyperemia (PORH; 5 minutes) was assessed before and during insulin perfusion. Red blood cell flux was measured continuously over each microdialysis site by laser-Doppler flowmetry. Cutaneous vascular conductance was calculated (CVC=flux/mean arterial pressure), normalized to maximum (%CVCmax), and presented as PORH area under the curve (AUC, %CVCmax• sec−1). Microvascular capillary recruitment was assessed as ΔAUC (pre-insulin AUC - insulin AUC). Insulin perfusion increased PORH in HC (pre-insulin: 4066±490 vs. insulin: 7848±978 AUC; p=0.03) but had no effect in GDM (pre-insulin: 3765±293 vs. insulin: 6196±779 AUC; p=0.26). Insulin perfusion did not increase PORH at the L-NAME site in either group (p&gt;0.05). Within groups, L-NAME perfusion reduced insulin-mediated capillary recruitment in HC (control: 3781±1109 vs. L-NAME: 470±945 ΔAUC; p=0.04) but not GDM (control: 2431±796 vs. L-NAME: -41±1014 ΔAUC, p=0.11). These data suggest that insulin-mediated capillary recruitment assessed by PORH in the cutaneous circulation is mediated by NO-dependent mechanisms in healthy women with a history of uncomplicated pregnancy and attenuated in healthy women with a history of GDM. This reduction in insulin-mediated microvascular responses may contribute to the increased risk of cardiovascular disease and type II diabetes in these women. UI Fraternal Order of Eagles Diabetes Research Center Catalyst Grant; NIH HL169201. 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.

Vascular Signaling Plasticity Reprograms Blood Delivery Mechanisms to Meet Fluctuating Neuronal Energy Needs

Neuronal computation is metabolically expensive and depends on precision delivery of energy substrates—oxygen and glucose—via tightly coordinated blood flow to ensure that energy demands are continually met. This is facilitated by neurovascular coupling (NVC)—a range of mechanisms matching neural activity to local blood flow. These NVC mechanisms are typically considered invariant, and whether they are reshaped according to ever-changing neuronal metabolic needs has not been examined. We present evidence that neural activity continually reprograms the blood flow control mechanisms embedded in the local vasculature, a process we refer to as ‘vascular signaling plasticity’ (VSP). Using an established enrichment paradigm, we find that animals housed in conditions that increase input to the barrel cortex for 7 days exhibit profound neuronal plasticity in this region. This resculpts local vascular reactivity to elevate blood delivery. Indeed, VSP results in increased basal capillary blood flow and augmented activity of vasodilatory agents in vivo manifesting as increased red blood cell (RBC) flux responses to capillary stimulation and upstream diameter changes measured using 2-photon laser scanning microscopy. Moreover, the sensitivity of capillaries to stimulation is also dramatically elevated in an ex vivo isolated capillary-arteriole preparation. Using K+-mediated capillary-to-arteriole electrical signaling as a springboard to study the molecular underpinnings of VSP, we find that this process induces a ~70% increase in the density of strong inward rectifier K+ (Kir2.1) currents in capillary endothelial cells, which profoundly augments the retrograde hyperpolarization generated by these channels to control upstream diameter at the level of the penetrating arteriole. Through whole-cell patch clamp electrophysiology, we characterize the mechanism of VSP induction and recapitulate this phenomenon in vitro. We validate our findings through Crispr/Cas9-mediated endothelial cell-specific knockout of the transcription factor responsible for VSP induction. Our data thus recast the vasculature as a plastic, brain-wide activity sensing network that is continually reshaped at the molecular level by local neuronal input, leading to precisely-tuned blood delivery to meet continually fluctuating neural energy needs. VSP represents a new dimension to brain plasticity that may underpin a range of vital physiological processes and is likely disrupted in numerous brain pathologies with a blood flow component. This work was supported by the American Heart Association (23POST1023086), and NIH grants 1DP2NS121347, 1R01AG066645, and 5R01NS115401. 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.

Inhibition of NF-κB Activation Improves Non-Nitric Oxide-Mediated Cutaneous Microvascular Function in Reproductive-Aged Healthy Women

PURPOSE: The human cutaneous circulation is used as an in vivo bioassay to examine mechanisms of systemic vascular function and dysfunction in health and disease. In cohorts of patients with accelerated cardiovascular disease risk, systemic interventions to investigate inflammatory mechanisms [e.g., oral salsalate; nuclear factor kappa-B (NF-κB) inhibitor] have been used to elucidate mechanisms underlying microvascular dysfunction. In healthy control subjects, inhibition of inflammatory mechanisms modestly reduces microvascular function. We hypothesize that inhibition of NF-κB activation may impair nitric oxide (NO)-mediated cutaneous microvascular function in reproductive-aged healthy women. METHODS: In a randomized, single-blind, placebo-controlled design, oral salsalate (1500mg/b.i.d./5 days) was used to assess the impact of systemic inflammation on cutaneous microvascular function. Two intradermal microdialysis fibers were placed into the ventral forearm skin of eleven healthy women [Mean (SEM): 34 (2) yrs]. Laser-Doppler flowmetry was used to measure cutaneous blood flow while increasing concentrations of acetylcholine (10−10 to 10−1 M; endothelium-dependent vasodilator) were perfused with a control (lactated Ringer’s) or a NO synthase inhibitor (15 mM NG-nitro-L-arginine methyl ester). Following the dose-response protocol, maximal cutaneous vasodilation was induced by increasing local skin temperature to 43°C and perfusing 28 mM sodium nitroprusside. Cutaneous vascular conductance (CVC) was calculated as the quotient of red blood cell flux over mean arterial pressure and normalized as a percentage of the site-specific maximum (%CVCmax). The NO-dependent contribution was calculated as the difference between the area under the dose-response curve (AUC) of the control and the NO synthase-inhibited sites. RESULTS: There was an overall main effect of salsalate treatment ( p &lt; 0.001). Both the control and NO synthase-inhibited sites shifted upwards following salsalate treatment (Placebo - Control: 45.78 (8.81)% vs NO synthase inhibited: 33.62 (8.10)%; Salsalate - Control: 56.30 (8.48)% vs NO synthase inhibited: 41.57 (7.85)%; both p &lt; 0.05). There was no change in the NO-dependent contribution between treatments (Placebo: 164.30 (35.40) AU vs Salsalate: 180.30 (51.17) AU; p=0.7028).CONCLUSION: Inhibition of NF-κB activation improved cutaneous microvascular function in reproductive-aged healthy women. This improvement was mediated via non-nitric oxide-dependent mechanisms. Supported by NIH Grant R01 HL161000 (LMA) and Diversity Supplement R01 HL161000-02S2 (VGC). 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.

Neuroinflammation increases oxygen extraction in a mouse model of Alzheimer’s disease

BackgroundNeuroinflammation, impaired metabolism, and hypoperfusion are fundamental pathological hallmarks of early Alzheimer’s disease (AD). Numerous studies have asserted a close association between neuroinflammation and disrupted cerebral energetics. During AD progression and other neurodegenerative disorders, a persistent state of chronic neuroinflammation reportedly exacerbates cytotoxicity and potentiates neuronal death. Here, we assessed the impact of a neuroinflammatory challenge on metabolic demand and microvascular hemodynamics in the somatosensory cortex of an AD mouse model.MethodsWe utilized in vivo 2-photon microscopy and the phosphorescent oxygen sensor Oxyphor 2P to measure partial pressure of oxygen (pO2) and capillary red blood cell flux in cortical microvessels of awake mice. Intravascular pO2 and capillary RBC flux measurements were performed in 8-month-old APPswe/PS1dE9 mice and wildtype littermates on days 0, 7, and 14 of a 14-day period of lipopolysaccharide-induced neuroinflammation.ResultsBefore the induced inflammatory challenge, AD mice demonstrated reduced metabolic demand but similar capillary red blood cell flux as their wild type counterparts. Neuroinflammation provoked significant reductions in cerebral intravascular oxygen levels and elevated oxygen extraction in both animal groups, without significantly altering red blood cell flux in capillaries.ConclusionsThis study provides evidence that neuroinflammation alters cerebral oxygen demand at the early stages of AD without substantially altering vascular oxygen supply. The results will guide our understanding of neuroinflammation’s influence on neuroimaging biomarkers for early AD diagnosis.

The Role of P-Selectin in Microvascular Hemodynamics and Cerebral Brain Volumes in Aging Sickle Cell Mice

Cerebral vasculopathy has been linked to the development of cognitive impairment in sickle cell disease (SCD). We have previously demonstrated that 13-month-old sickle cell mice recapitulate features of cerebral vasculopathy such as tortuous vessels, microthrombi, and hypoperfusion seen in adults with SCD. Histologically, we also showed these mice have increased cerebral microvascular deposition of P-selectin and more frequent and larger microinfarcts compared to matched controls. We further showed that these mice developed evidence of cognitive deficit compared to matched controls. Based on these observations, we hypothesized P-selectin may play a critical role in development of cerebral micro vasculopathy and downstream pathologic sequalae such as microinfarcts by enhancing leukocyte-endothelial interactions. Furthermore, abundant evidence from non-sickle mice shows that microinfarcts can exacerbate small vessel changes including gray matter volume loss. Building on our prior work, in this study, we examined the effect of P-selectin deficiency on cerebral microvascular hemodynamics and leukocyte-endothelial interaction and well as changes in cortical and subcortical gray matter volume in aged sickle mice. Male, P-selectin knockout (Psel KO) or intact (Psel WT) chimeric mice were generated by transplanting control (AA) or sickle (SS) bone marrow into P-selectin knockout (Psel -/-) or C57BL/6 (B6) recipients. To assess the impact of vasculopathy and brain gray matter volume changes longitudinally, male mice were assessed at 12-, 14- or 16-month post-transplant. Hemodynamics (mean velocity, red blood cell (RBC) flux, white blood cell stalls in capillaries as well as venules) were obtained from line-scan images acquired using in-vivo two-photon microscopy, using custom and validated MATLAB scripts. Gray matter volumes in 26 cortical and subcortical brain regions with relevance to cognitive function, were derived from parcellation of T2-weighted magnetic resonance imaging after non-linear registration to Allen brain atlas T1 anatomical space. Parcellation was accomplished by registering the Paxinos atlas to the mouse T2 now in Allen space. Brain volume analyses was accomplished using Analyze 12 software. After the completion of in-vivo studies, brains were extracted for immunohistochemistry analysis. Statistical analysis was performed using two-way ANOVA. The breakdown of the mice included in this study are; 14 B6 AA, 12 B6 SS, 12 Psel KO AA and 13 Psel KO SS. Given the high attrition rate in older mice, data from 12-, 14- and 16-month-old cohorts were combined. Mean age of B6 AA cohort was 13.1 months, 12.8 months for B6 SS, 13. 9 months for Psel KO AA and 13.6 months for Psel KO SS mice and were not statistically different. Psel KO sickle mice had a significantly lower mean capillary RBC velocity (1.733 mm/s vs 4.717 mm/s, p &amp;lt; 0.01) compared to Psel WT SS mice. In addition, Psel KO SS mice had relatively smaller (more normal) capillary diameter compared to Psel WT SS mice (6.248 um vs 8.613 um, p &amp;lt; 0.001). Interestingly, there was no statistically significant difference in RBC flux between Psel KO SS and Psel WT SS mice, however Psel KO SS mice show a lower red blood cell flux similar to that seen in Psel WT AA mice ( Figure 1). Of the 26 brain regions that were assessed, Psel KO SS mice had larger measured gray matter volume in the frontal association cortex (3.01 ± 0.77 vs 3.66± 0.33 mm 3, p= 0.0083), prelimbic cortex (1.72 ± 0.27 vs 1.95 ± 0.17 mm 3, p=0.0079), hippocampus (17.67 ± 1.56 vs 16.21± 1.97 mm 3, p=0.01)( Figure 1) including other regions such as lateral (2.12 ± 0.19 vs 1.88 ± 0.31 vs mm 3 p=0.0096) medial (1.84± 0.16 vs 1.64 ± 0.26 mm 3, p=0.01), and ventral orbital cortex( 1.95± 0.17 vs1.72 ± 0.27 mm 3, p=0.01) and dorsolateral olfactory tract (1.46 6± 0.13 vs 1.31 ± 0.20 mm 3, p=0.023 compared to the Psel WT SS mice (data not shown). In conclusion, non-hematopoetic P-selectin deficiency improves cerebral vasculopathy as demonstrated by normalization of hemodynamics in sickle mice. We also show that Psel KO SS mice had larger brain gray matter volume in regions involved in cognitive function. Additional studies are needed to identify the underlying mechanism of improvement in brain gray matter volume as well as whether P-selectin could be potential target for reducing SCD associated neurological complications.

Angiotensin II type 2 receptor-mediated dilation is greater in the cutaneous microvasculature of premenopausal women compared with men.

Differential activation of the renin-angiotensin system (RAS) likely contributes to sex differences in cardiovascular outcomes in premenopausal women compared with age-matched men. Women demonstrate reduced activation of the vasoconstrictor angiotensin II type 1 receptors (AT1R) compared with men, and evidence suggests that women also likely have increased sensitivity of the vasodilatory angiotensin II type 2 receptors (AT2R). However, few in vivo studies have directly examined sex differences in AT2R-mediated dilation, or the balance between AT1R- and AT2R-mediated vascular responses in humans. Using the cutaneous microcirculation as a model, we hypothesized that AT2R-mediated dilation would be greater in premenopausal women compared with men, and that AT1R-blockade would augment AT2R-mediated dilation to a greater extent in men than in women. Twelve healthy women (22 ± 3 yr) and 12 men (23 ± 5 yr) had two intradermal microdialysis fibers placed in the ventral forearm for graded infusions of compound 21 (AT2R agonist; 10-12 to 10-8 M) in a control fiber site and a site treated with 43 µM losartan (AT1R antagonist). Red blood cell flux was measured continuously by laser-Doppler flowmetry, and cutaneous vascular conductance [CVC = flux/mean arterial pressure (MAP)] was normalized to maximum [%max; 28 mM sodium nitroprusside (SNP) + 43 °C]. Women had greater AT2R-mediated dilation compared with men (women: 25 ± 4 vs. men: 15 ± 2%max, P = 0.03). Local AT1R inhibition increased AT2R-mediated dilation in men (losartan: 26 ± 4 vs. control: 15 ± 2%max, P < 0.001) but had no effect in women (losartan: 27 ± 6 vs. control: 25 ± 4%max, P > 0.05). These data suggest that premenopausal women have a greater AT2R-mediated vasodilation response than men, and that AT1R activation inhibits AT2R-mediated dilation in men, but not in women.NEW & NOTEWORTHY Premenopausal women have greater protection against cardiovascular disease than age-matched men. However, the role of vasoconstrictor angiotensin II type 1 receptors (AT1R) and vasodilatory angiotensin II type 2 receptors (AT2R) in mediating these sex differences is unclear. Here, we demonstrate that women have greater AT2R-mediated vasodilation than men and that AT1R negates AT2R-mediated dilation in men, but not in women.

Abstract P209: Six Weeks Oral Losartan Treatment Improves Endothelium-dependent Dilation In Normotensive Women With A History Of Preeclampsia

Women with a history of preeclampsia have a 4-fold increased risk of cardiovascular disease compared to women who had a healthy pregnancy. These women demonstrate microvascular endothelial dysfunction, mediated by reduced nitric oxide (NO)-dependent dilation and increased sensitivity to angiotensin II. We hypothesized that systemic angiotensin II type 1 receptor (AT 1 R) inhibition would improve endothelium- and NO-dependent dilation in the microvasculature of women with a history of preeclampsia. Seven normotensive (seated SBP 118±6; DBP 78±6 mmHg) women (33±6 years of age, 11±7 months postpartum) with a history of preeclampsia participated in a double-blind placebo-controlled crossover study. Following 6 weeks of placebo and losartan treatment (50 mg/day), participants wore a 24-hour blood pressure monitor and completed 1 study visit in which 2 intradermal microdialysis fibers were placed in the skin of the ventral forearm for graded infusions of acetylcholine (ACh, 10 -7 -10 2 mM) or ACh + 15 mM N G nitro L-arginine methyl ester (L-NAME; NO synthase inhibitor) to assess endothelium- and NO-dependent dilation, respectively. Red blood cell flux was measured over each microdialysis site by laser-Doppler flowmetry. Cutaneous vascular conductance was calculated (CVC=Doppler flux/mean arterial pressure) and normalized to maximum (%max; 28 mM SNP + 43°C). Systemic losartan treatment augmented endothelium-dependent (losartan: 96±4 vs placebo: 70±14%max; P &lt;0.001) and NO-dependent (losartan: 35±14 vs placebo: 23±8%; P &lt;0.001) dilation. There was no effect of treatment on 24-hour systolic blood pressure (losartan: 117±4 vs placebo: 117±8 mmHg), diastolic blood pressure (losartan: 72±5 vs placebo: 71±5 mmHg) or mean arterial pressure (losartan: 92±4 vs placebo: 92±6 mmHg; all P&gt;0.05 ). Losartan treatment increased endothelium-dependent vasodilation via NO-mediated pathways in the absence of changes in blood pressure in women with a history of preeclampsia. These data suggest that systemic AT 1 R inhibition may be a viable therapeutic approach to treat persistent microvascular dysfunction in otherwise healthy women who have had preeclampsia.

Red Blood Cell Partitioning Using a Microfluidic Channel with Ladder Structure.

This study investigated the partitioning characteristics of red blood cells (RBCs) within capillaries, with a specific focus on ladder structures observed near the end of the capillaries. In vitro experiments were conducted using microfluidic channels with a ladder structure model comprising six bifurcating channels that exhibited an anti-parallel flow configuration. The effects of various factors, such as the parent channel width, distance between branches, and hematocrit, on RBC partitioning in bifurcating channels were evaluated. A decrease in the parent channel width resulted in an increase in the heterogeneity in the hematocrit distribution and a bias in the fractional RBC flux. Additionally, variations in the distance between branches affected the RBC distribution, with smaller distances resulting in greater heterogeneity. The bias of the RBC distribution in the microchannel cross section had a major effect on the RBC partitioning characteristics. The influence of hematocrit variations on the RBC distribution was also investigated, with lower hematocrit values leading to a more pronounced bias in the RBC distribution. Overall, this study provides valuable insights into RBC distribution characteristics in capillary networks, contributing to our understanding of the physiological mechanisms of RBC phase separation in the microcirculatory system. These findings have implications for predicting oxygen heterogeneity in tissues and could aid in the study of diseases associated with impaired microcirculation.

Differential reductions in the capillary red-blood-cell flux between retina and brain under chronic global hypoperfusion.

It has been hypothesized that abnormal microcirculation in the retina might predict the risk of ischemic damages in the brain. Direct comparison between the retinal and the cerebral microcirculation using similar animal preparation and under similar experimental conditions would help test this hypothesis. We investigated capillary red-blood-cell (RBC) flux changes under controlled conditions and bilateral-carotid-artery-stenosis (BCAS)-induced hypoperfusion, and then compared them with our previous measurements performed in the brain. We measured capillary RBC flux in mouse retina with two-photon microscopy using a fluorescence-labeled RBC-passage approach. Key physiological parameters were monitored during experiments to ensure stable physiology. We found that under the controlled conditions, capillary RBC flux in the retina was much higher than in the brain (i.e., cerebral cortical gray matter and subcortical white matter), and that BCAS induced a much larger decrease in capillary RBC flux in the retina than in the brain. We demonstrated a two-photon microscopy-based technique to efficiently measure capillary RBC flux in the retina. Since cerebral subcortical white matter often exhibits early pathological developments due to global hypoperfusion, our results suggest that retinal microcirculation may be utilized as an early marker of brain diseases involving global hypoperfusion.

Nitric oxide‐mediated cutaneous microvascular function is not altered in middle‐aged‐to‐older adults following mild SARS‐CoV‐2 infection: A pilot study

We tested the hypothesis that post-COVID-19 adults (PC) would have impaired cutaneous nitric oxide (NO)-mediated vasodilation compared to controls (CON). We performed a cross-sectional study including 10 (10 F/0 M, 69 ± 7 years) CON and 7 (2 F/5 M, 66 ± 8 years) PC (223 ± 154 days post-diagnosis). COVID-19 symptoms severity (survey) was assessed (0-100 scale for 18 common symptoms). NO-dependent cutaneous vasodilation was induced by a standardized 42°C local heating protocol and quantified via perfusion of 15 mM NG-nitro-L-arginine methyl ester during the plateau of the heating response (intradermal microdialysis). Red blood cell flux was measured with laser-Doppler flowmetry. Cutaneous vascular conductance (CVC = flux/mm Hg) was presented as a percentage of maximum (28 mM sodium nitroprusside +43°C). All data are means ± SD. The local heating plateau (CON: 71 ± 23% CVCmax vs. PC: 81 ± 16% CVCmax , p = 0.77) and NO-dependent vasodilation (CON: 56 ± 23% vs. PC: 60 ± 22%, p = 0.77) were not different between groups. In the PC group neither time since diagnosis nor peak symptom severity (46 ± 18 AU) correlated with NO-dependent vasodilation (r < 0.01, p = 0.99 and r = 0.42, p = 0.35, respectively). In conclusion, middle-aged and older adults who have had COVID-19 did not have impaired NO-dependent cutaneous vasodilation. Additionally, in this cohort of PC, neither time since diagnosis nor symptomology were related to microvascular function.

In vivo pressure-flow relation of human cutaneous vessels following prolonged iterative exposures to hypergravity.

The study examined intra- and interlimb variations in cutaneous vessel responsiveness to acute and repeated transmural pressure elevations. In 11 healthy men, red blood cell flux was assessed via laser-Doppler flowmetry on both glabrous and nonglabrous skin regions of an arm (finger and forearm) and leg (toe and lower leg), across a wide range of stepwise increasing distending pressures imposed in the vessels of each limb separately. The pressure-flux cutaneous responses were evaluated before and after 5 wk of intermittent (40 min, 3 sessions per week) exposures to hypergravity (∼2.6-3.3 G; G training). Before and after G training, forearm and lower leg blood flux were relatively stable up to ∼210 and ∼240 mmHg distending pressures, respectively; and then they increased two- to threefold (P < 0.001). Finger blood flux dropped promptly (P < 0.001), regardless of the G training (P = 0.64). At ≤120-mmHg distending pressures, toe blood flux enhanced by ∼40% (P ≤ 0.05); the increase was augmented after the G training (P = 0.01). At high distending pressures, toe blood flux dropped by ∼70% in both trials (P < 0.001). The present results demonstrate that circulatory autoregulation is more pronounced in glabrous skin than in nonglabrous skin, and in nonglabrous sites of the leg than in those of the arm. Repetitive high-sustained gravitoinertial stress does not modify the pressure-flow relationship in the dependent skin vessels of the arm nor in the nonglabrous sites of the lower leg. Yet it may partly inhibit the myogenic responsiveness of the toe's glabrous skin.

Endothelial Piezo1 channel controls cerebral blood flow

Cerebral blood flow is controlled to meet the ever-changing demands of active neurons. Brain capillaries are equipped with sensors of neurovascular coupling agents released from neurons/astrocytes onto the outer wall of a capillary. While capillaries can translate external signals into electrical and Ca2+ changes, control mechanisms from the lumen are less clear. The continuous flux of red blood cells and plasma through narrow-diameter capillaries imposes mechanical forces on the luminal (inner) capillary wall. We have recently discovered that the mechanosensitive Piezo1 channels operate as mechanosensors in CNS capillaries. Whether—and if so how—Piezo1-mediated mechanosensation regulates CBF is not known. Using genetically engineered mice in which endothelial Piezo1 is ablated (Piezo1 EC-KO ) or mutated (Piezo1 EC-mut ), we assessed channel activity and CBF. We provide evidence that Piezo1 plays an important role in CBF control and profoundly affects functional hyperemia during somatosensory stimulation. These observations are of profound significance for the control of brain blood flow in health and in disorders where hemodynamic forces are disrupted, such as hypertension. The American Heart Association (20CDA35310097), the National Institute of General Medical Sciences (P20GM135007), the Totman Medical Research Trust, the Larner College of Medicine, University of Vermont, and the Cardiovascular Research Institute of Vermont. This is the full abstract presented at the American Physiology Summit 2023 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 Health is Reduced in Frequent Cannabis Users

BACKGROUND: Microvascular dysfunction is a marker of endothelial vascular damage and is considered one of the earliest indicators of cardiovascular disease (CVD) development. Frequent cannabis use has been previously linked to increased CVD risk. However, whether microvascular health is impacted by cannabis use in otherwise healthy young adults has not been explored yet. PURPOSE: The purpose of this study was to investigate the impact of frequent cannabis usage on microvascular health in young healthy adults. METHODS: Thirteen frequent cannabis users (CU, 5 males and 8 females; age:23±3 yo; used cannabis 2.5±2 days/week) and thirteen demographical matched never users (NU, 5 males and 8 females; age:22±1 yo) completed a comprehensive assessment of microvascular function. Microvascular health was assessed using Laser Doppler Imaging coupled with Post Occlusive Reactive Hyperemia (PORH), to evaluate overall microvascular function, and Local Thermal Hyperemia (LTH) to evaluate neurogenic and endothelial mechanisms of vascular function. Blood flow was calculated as cutaneous vascular conductance, considering red blood cell flux and mean arterial blood pressure. RESULTS: Cannabis users exhibited significantly ( p=0.01) lower microvascular function when compared to never users (PORH, CU: 0.68±0.18 vs. NU: 0.85±0.14 mmHg/PU). Of note, microvascular function was significantly ( p=0.03) reduced in those that use cannabis more than 2.5 days/week (n=5; 0.55±0.10) when compared to those who used it less frequently (n=8; 0.76±0.18 mmHg/PU). In addition, neurogenic mechanisms (CU:1.31±0.57 vs. NU: 1.89±0.48 mmHg/PU; p=0.009) and endothelial mechanisms (CU: 1.61±0.44 vs. NU: 1.96±0.35 mmHg/PU; p=0.03) were significantly lower in cannabis users when compared to never users. CONCLUSIONS: Our results suggest that frequent cannabis users exhibit reduced microvascular health in comparison to never users, suggesting worse long-term CVD outcomes. Specifically, those that use cannabis more than 2 times per week exhibit lower microvascular function. In addition, cannabis use negatively impact neurogenic and endothelial microvascular mechanisms that warrant further investigation. This is the full abstract presented at the American Physiology Summit 2023 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.

Angiotensin II type 2 receptor-mediated dilation is greater in the cutaneous microvasculature of premenopausal women compared to men

Sex differences in the activation of the renin-angiotensin system (RAS) likely contribute to differences in cardiovascular outcomes in premenopausal women compared to age-matched men. It is established that women have a reduced activation of the vasoconstrictor angiotensin II – angiotensin II type 1 receptor (AT 1 R) pathway. Emerging evidence suggests that this may be mediated by a shift toward the more recently described vasodilatory RAS, including increased sensitivity of the vasodilatory angiotensin II type 2 receptor (AT 2 R). However, few in vivo studies have directly examined sex differences in AT 2 R-mediated dilation, or the balance between AT 1 R- and AT 2 R-mediated vascular responses in humans. Using the cutaneous microcirculation as a model, we hypothesized that AT 2 R-mediated dilation would be greater in premenopausal women compared to men, and that AT 1 R-blockade would augment AT 2 R-mediated dilation to a greater extent in men than in women. Eight healthy women (22±3 years) and 11 healthy men (23±5 years) participated in 1 experimental visit. Two intradermal microdialysis fibers were placed in the skin of the ventral forearm for graded infusions of either compound 21 (C21, AT 2 R agonist; 10 -12 - 10 -3 mol/L) alone or C21 + 43 μmol/L losartan (AT 1 R antagonist). Red blood cell flux was measured over each microdialysis site by laser-Doppler flowmetry. Cutaneous vascular conductance was calculated (CVC=doppler flux/mean arterial pressure) and normalized to maximum (%CVCmax; 28mM SNP+43°C). Women had a greater peak vasodilation response to C21 compared to men (27.2±5.7 versus 18.2±2.7 %CVCmax; p=0.03). AT 1 R-inhibition augmented peak C21-mediated dilation in men (31.3±4.5 versus 18.2±2.7 %CVCmax; p=0.009) but had no effect in women (24.5±6.5 versus 27.2±5.7 %CVCmax; p=0.34). These data suggest that premenopausal women have a greater AT 2 R-mediated vasodilation response than men, and that AT 1 R activation inhibits AT 2 R-mediated dilation in men, but not in women. This study is supported by National Heart, Lung, and Blood Institute Grant R00HL138133. Clinicaltrials.gov identifier: NCT05576155 This is the full abstract presented at the American Physiology Summit 2023 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.

No impact of biological sex on nitric oxide contribution to cutaneous vascular response to 39ºC local heating

Purpose: The contribution of endothelial nitric oxide (NO) to vasodilation (%NO contribution) is a significant indicator of risk of cardiovascular disease development. Local skin heating to either 42 ºC or 39 ºC is used to determine mechanisms of vasodilation in health and disease, specifically to investigate %NO contribution. Women have lower %NO contribution in the cutaneous vasculature than men in the early follicular phase of the menstrual cycle, when the circulating vasoactive reproductive hormones are at their lowest concentration. However, this phase represents only a brief portion of the menstrual cycle. We aimed to determine the overall impact of biological sex on %NO contribution to cutaneous vasodilation utilizing a 39ºC local heating protocol, which better isolates the endothelial NO-synthase pathway. We tested women randomly during any phase of the menstrual cycle. We hypothesized that women would demonstrate greater NO-dependent cutaneous vasodilation than men in response to 39ºC local heating. Methods: Data are represented as mean(SD). An intradermal microdialysis fiber was placed in the ventral forearms of 12 men and 13 women [24.2(4.6) years]. Local heaters and laser-Doppler flowmetry probes were used to measure red blood cell flux (perfusion units, PU). Cutaneous vascular conductance (CVC) was calculated as laser-Doppler PU/mean arterial pressure. A standard 39ºC local heating protocol was conducted wherein PU was continuously collected at rest (10 minutes), then the local temperature was increased to 39ºC. After PU reached a steady plateau (~40 minutes), the NO synthase inhibitor 15 mM NG-nitro-L-arginine methyl ester (L-NAME) was perfused. Maximal vasodilation was induced by heating to 43ºC and perfusing 28 mM sodium nitroprusside and normalized to %CVCmax. %NO contribution was calculated as the absolute percentage difference between %CVCmax of 39ºC plateau and %CVCmax of L-NAME steady-state. We compared both CVC and %CVCmax between groups with two-way ANOVA and the %NO contribution with unpaired t-tests. Results: The %NO contribution was not different between sexes [men 48(23)%, women 39(17)%; P = 0.26]. There was no effect of sex on either absolute CVC [men 0.717(0.29) PU, women 0.73(0.48) PU at 39ºC phase] or %CVCmax [men 69(31)%, women 54(20)% at 39ºC phase] at any stage of the 39ºC local heating protocol (main effects P ≥ 0.08). Conclusion: These data indicate there is no impact of biological sex on the vasodilatory response of the cutaneous vasculature to 39ºC local heating in young healthy adults when women are tested at random across the menstrual cycle. Funding: National Institutes of Health Grant T-32-5T32AG049676 This is the full abstract presented at the American Physiology Summit 2023 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.