Arteriolar Diameter Research Articles

Propofol But Not Desflurane Maintains Rat Cerebral Arteriolar Responses to Acetylcholine During Acute Hyperglycemia.

Acute hyperglycemia causes vascular endothelial dysfunction in various organs including the cerebral vessels. It is associated with increased mortality and morbidity in the perioperative period. The impact of anesthetic agents on cerebral vasodilatory responses during hyperglycemia remains unclear. We investigated endothelial function in rat cerebral arterioles during acute hyperglycemia, under propofol or desflurane anesthesia. A closed cranial window preparation was used to measure changes in pial arteriole diameter induced by topical application of acetylcholine (ACh), an endothelium-dependent vasodilator, in rats anesthetized with propofol or desflurane. Pial arteriole responses to ACh were measured during normoglycemia and hyperglycemia. We then investigated whether the response of cerebral arterioles to acute hyperglycemia under propofol anesthesia were related to propofol or its vehicle, intralipid. ACh resulted in a dose-dependent dilation of cerebral arterioles during propofol and desflurane anesthesia under normoglycemic conditions. The vasodilatory effects of ACh were also maintained under hyperglycemic conditions during propofol anesthesia, but the vasodilator response to ACh was significantly impaired during hyperglycemia compared with normoglycemia with desflurane anesthesia. The vasodilatory effects of ACh were maintained during normoglycemia and hyperglycemia in rats receiving propofol or intralipid. Rat pial arteriole responses to ACh are maintained during conditions of acute hyperglycemia with propofol anesthesia but suppressed compared with normoglycemia with desflurane anesthesia.

Long-term impairment of neurovascular coupling following experimental subarachnoid hemorrhage

CO2-reactivity and neurovascular coupling are sequentially lost within the first 24 h after subarachnoid hemorrhage (SAH). Whether and when these impairments recover is not known. Therefore, we investigated the reactivity of pial and intraparenchymal vessels by in vivo two-photon microscopy one month after experimental SAH. C57BL/6 mice were subjected to either sham surgery or SAH by filament perforation. One month later, cerebral blood flow following CO2-challenge and forepaw stimulation was assessed by laser Doppler fluxmetry. Diameters of pial and intraparenchymal arterioles were quantified by in vivo two-photon microscopy. One month after SAH, pial and parenchymal vessels dilated in response to CO2. Neurovascular coupling was almost completely absent after SAH: vessel diameter did not change upon forepaw stimulation compared to a 20% increase in sham-operated mice. The current results demonstrate that neurovascular function differentially recovers after SAH: while CO2-reactivity normalizes within one month after SAH, neurovascular coupling is still absent. These findings show an acute and persistent loss of neurovascular coupling after SAH that may serve as a link between early brain injury and delayed cerebral ischemia, two distinct pathophysiological phenomena after SAH that were so far believed not to be directly related.

Retinal Endothelial Function, Physical Fitness and Cardiovascular Risk: A Diagnostic Challenge.

IntroductionDynamic retinal vessel analysis (DVA) is a new non-invasive method to quantify microvascular endothelial dysfunction by flicker light-induced dilatation (FID). FID has been shown to be impaired in type 2 diabetes as well as heart failure. The aim of the study was to analyze FID in healthy active versus healthy sedentary and cardiovascular (CV) risk patients in addition to corresponding static vessel diameters.MethodsThirty-one healthy active (HA, mean age 60 ± 8 years), 33 healthy sedentary individuals (HS, 59 ± 7 years) and 76 sedentary patients with increased CV risk (SR, 58 ± 6 years) were included in this cross-sectional study. Group differences in CV risk factors and cardiorespiratory fitness, maximal arteriolar (ADmax) and venular (VDmax) dilatation as well as the arteriolar (AFarea) and venular (VFarea) area under the flicker curve were analyzed. The central retinal arteriolar and venular diameters were used to calculate the arteriolar-to-venular diameter ratio (AVR).ResultsHS [ADmax = 3.5 (2.1)%; AFarea = 48.2 (31.9)%∗s] showed higher FID compared to SR [ADmax = 2.7 (1.8)%, p = 0.021; AFarea = 34.5 (26.5)%∗s, p = 0.006] and HA [AFarea = 32.8 (23.1)%∗s, p = 0.029]. HA and SR did not significantly differ. HA had a higher AVR (0.87 ± 0.05) compared to HS (0.83 ± 0.04, p < 0.001) with further deterioration in SR (0.79 ± 0.05, p < 0.001). Interestingly, 28 participants had impaired FID but normal AVR and 43 participants had normal FID but impaired AVR.DiscussionFID can differentiate between sedentary low and high risk individuals. However, FID in healthy active persons (HA) seemed impaired with a concomitant higher AVR. We postulate that lower FID in HA may be explained by predilatated arterioles and a reduced dilatation reserve. We recommend combination of FID with analysis of retinal vessel diameters to differentiate functional non-responders from manifest microvascular endothelial dysfunction and, thereby, improve microvascular risk stratification in a personalized medicine approach.Clinical Trial RegistrationClinicalTrials.gov: NCT02796976 (https://clinicaltrials.gov/ ct2/show/NCT02796976).

Reduced baseline diameter and contraction of peripheral retinal arterioles immediately after remote ischemia in diabetic patients.

Remote ischemic conditioning (RIC) implies that transient ischemia in one organ can affect blood flow and protect from ischemia in another remote organ such as the retina. The purpose of the present study was to investigate the effect of RIC on the diameter of retinal arterioles in patients with diabetic retinopathy and whether this effect differs among peripheral and macular vessels. In twenty type 1 diabetes patients aged 20-31years, the Dynamic Vessel Analyzer (DVA) was used to measure diameters of peripheral and macular arterioles during rest, isometric exercise, and flicker stimulation. Measurements were obtained before, immediately after, and 1h after RIC, and were compared to responses obtained from normal persons. The reduced baseline diameter (p < 0.009) and contraction of peripheral retinal arterioles during isometric exercise (p = 0.025) observed immediately after RIC in normal persons were absent in the studied diabetic patients. RIC affects the diameter of peripheral but not macular arterioles in normal persons, but the response is abolished in diabetic patients. NCT03906383.

Hypercapnia Impairs Vasoreactivity to Changes in Blood Pressure and Intraocular Pressure in Rat Retina.

The balance between oxygen and carbon dioxide sets the resting tone (or diameter) of retinal blood vessels. Eyes that are hypercapnic use up their "vasodilatory reserve" and therefore fail to respond adequately to changes in intraocular or blood pressure. Retinal vessels are regulated by both myogenic and metabolic mechanisms. We considered whether alteration of metabolic status would modify the vascular response to ocular perfusion pressure (OPP) lowering in rat retina. In pentobarbital anesthetized adult Brown-Norway rats, normocapnia or hypercapnia was achieved by artificially ventilating animals with air or 5% carbon dioxide in ~30% oxygen, respectively. Ocular perfusion pressure was gradually reduced to ~20 mmHg by either lowering blood pressure (slowly drawing blood from a femoral artery/vein) or manometrically increasing intraocular pressure under normocapnic or hypercapnic conditions. In all four groups (n = 7 eyes for each), a confocal scanning laser ophthalmoscope was used to acquire image sequences centered on the optic nerve throughout pressure modification. The diameter of arterioles and venules at various OPP levels was measured and expressed as percentage relative to their own baseline. The response of arterioles and venules to OPP lowering was compared between normocapnic and hypercapnic groups. Average arterial carbon dioxide partial pressures were 36.9 ± 2.6 mmHg in normocapnic and 64.1 ± 5.9 mmHg in hypercapnic (P < .001) animals. In the normocapnic groups, blood pressure lowering and intraocular pressure elevation resulted in significant vasodilation of both arterioles and venules (P < .0001). In the hypercapnic groups, OPP lowering-induced vasodilation was significantly attenuated compared with the corresponding normocapnic groups (P < .0001 for both, two-way analysis of variance). Hypercapnia significantly modified myogenic vascular autoregulation in response to OPP reduction.

Effect of smoking cessation on the parameters of microcirculation in arterial hypertension

Aim. To identify changes of microcirculatory parameters in former hypertensive smokers. &#x0D; Methods. Videobiomicroscopy was used to study the microcirculation of bulbar conjunctiva in 94 patients suffering from arterial hypertension. The results of former smokers (n=21, average age 41.6±2.5 years) were compared to those of smokers (n=32, average age 36.8±2.2 years) and non-smokers (n=41, average age 40.5±2.3 years). &#x0D; Results. The average diameter of arterioles, the arteriolar-to-venular ratio and the average diameter of the capillaries were minimal in the group of smokers with hypertension. In former smokers, these indicators increased significantly (p1

Retinal vessel reactivity is not attenuated in patients with type 2 diabetes compared with matched controls and is associated with peripheral endothelial function in controls

Background and aimsAttenuated retinal vasoreactivity in patients with type 2 diabetes preceding diabetic retinopathy development has been proposed to reflect local endothelial dysfunction.Whether retinal vessel reactivity is associated with peripheral endothelial dysfunction and large artery stiffness in patients with type 2 diabetes remains to be elucidated. MethodsTwenty patients with type 2 diabetes without retinopathy and 20 sex- and age matched controls (diabetes duration: 9.9 years (range 6.0;12.4), 40% male, age: 66.5 ± 7.3 (diabetes) and 65.2 ± 7.6 years (controls)) were included. Endothelial function was assessed using EndoPAT. Arterial stiffness was assessed by carotid-femoral pulse wave velocity using the SphygmoCor. Retinal blood supply regulation was examined by retinal arteriolar diameter change during 1) isometric exercise (hand-weight lifting), 2) exposure to flickering lights, and 3) a combined stimulus of 1) + 2) using the Dynamic Vessel Analyzer. ResultsNo significant differences were observed in retinal vessel reactivity in T2DM patients compared to controls. Endothelial function was associated with mean arteriolar diameter change during only the combination intervention, (Beta = 0.033 [0.0013;0.064], p = 0.042) in the overall population of patients and controls. When groups were analyzed separately, the associations was statistically significant only in controls. However, formal test for interaction was not statistically significant, p = 0.40. No association was observed between pulse wave velocity and retinal arteriolar %-diameter change in patients or controls. ConclusionPeripheral endothelial function was associated with retinal arteriolar diameter change in the combined sample. The association seemed to be driven primarily by the controls. Our findings indicate that peripheral endothelial function is reflective of endothelial function in the retina mainly in subjects without T2DM, whereas an association in T2DM without retinopathy was not observed. Further studies are needed in T2DM patients with more advanced retinopathy.

Age-related impairment of neurovascular coupling responses: a dynamic vessel analysis (DVA)-based approach to measure decreased flicker light stimulus-induced retinal arteriolar dilation in healthy older adults.

Aging is a major risk factor for vascular cognitive impairment and dementia (VCID). Recent studies demonstrate that cerebromicrovascular dysfunction plays a causal role in the development of age-related cognitive impairment, in part via disruption of neurovascular coupling (NVC) responses. NVC (functional hyperemia) is responsible for adjusting cerebral blood flow to the increased energetic demands of activated neurons, and in preclinical animal models of aging, pharmacological restoration of NVC is associated with improved cognitive performance. To translate these findings, there is an increasing need to develop novel and sensitive tools to assess cerebromicrovascular function and NVC to assess risk for VCID and evaluate treatment efficacy. Due to shared developmental origins, anatomical features, and physiology, assessment of retinal vessel function may serve as an important surrogate outcome measure to study neurovascular dysfunction. The present study was designed to compare NVC responses in young (< 45years of age; n = 18) and aged (> 65years of age; n = 11) healthy human subjects by assessing flicker light-induced changes in the diameter of retinal arterioles using a dynamic vessel analyzer (DVA)-based approach. We found that NVC responses in retinal arterioles were significantly decreased in older adults as compared with younger subjects. We propose that the DVA-based approach can be used to assess NVC, as a surrogate cerebromicrovascular outcome measure, to evaluate the effects of therapeutic interventions in older individuals.

Hemoglobin A1c and retinal arteriolar narrowing in children with type 1 diabetes: the diagnostics of early atherosclerosis risk in kids study.

Microvascular alterations play a key role in the development of diabetes complications. Retinal vessel analysis is a unique method to examine microvascular changes in brain-derived vessels. Sixty-seven pediatric and adolescent type 1 diabetes patients and 58 healthy control persons (mean age 12.4 ± 2.9 years) underwent non-mydriatic retinal photography of both eyes. Central retinal arteriolar and central retinal venular (CRVE) diameter equivalents as well as the arteriolar-to-venular ratio were calculated using a semiautomated software. All anthropometric and laboratory parameters were measured according to standardized procedures for children. Retinal vessel diameter did not differ between type 1 diabetic children and healthy controls. However, there was an independent association of higher hemoglobin A1c (HbA1c) levels with arteriolar narrowing. Arteriolar narrowing of 5.4 μm was observed with each percent increase in HbA1c. Longer duration of diabetes was associated with wider retinal arterioles. CRVE was not associated with diabetes duration or HbA1c. Microvascular arteriolar alterations are already present in childhood and may indicate subclinical atherosclerosis and increased risk of diabetes complications later in life. Future research will have to investigate the potential use of retinal vessel diameters for treatment monitoring and guidance of therapy in children.

The Diameter of Retinal Arterioles Is Unaffected by Intravascular Administration of the Adenosine A2A Receptor Agonist Regadenoson in Normal Persons

Background: The neurotransmitter adenosine has been proposed to be involved in the pathogenesis of diabetic retinopathy, which may be due to the vasoactive properties of the compound. Previous studies have shown that adenosine can affect the tone of retinal arterioles in vitro to induce dilatation mediated by A_2A and A_2Breceptors and constriction mediated by A₁ and A₃ receptors. Purpose: To investigate effects of intravenous administration of the adenosine A_2A receptor agonist regadenoson on the diameter of retinal vessels in vivo. Method: The diameter responses of larger retinal arterioles and venules were evaluated using the dynamic vessel analyser in 20 normal persons (age 22–31 years) after intravenous administration of the adenosine A_2A receptor agonist regadenoson during exposure to systemic normoxia and hypoxia. Results: The diameter of retinal arterioles and venules increased significantly during stimulation with flickering light (p < 0.0001). Regadenoson reduced the flicker-induced dilatation of venules during normoxia (p = 0.0006), but otherwise had no effect on vessel diameters (p > 0.08 for all comparisons). Conclusions:Intravenous administration of the adenosine A_2A receptor agonist regadenoson had no significant effect on the diameter of retinal arterioles. Future studies should investigate differential effects of intra- and extravascular administration of adenosine receptor agonists on retinal vessels.

Retinal vascular abnormalities in schizophrenia and bipolar disorder: A window to the brain.

The examination of retinal microvascular abnormalities through fundus photography is currently the best available non-invasive technique for assessment of cerebral vascular status. Several studies in the last decade have reported higher incidences of adverse cerebrovascular events in Schizophrenia (SCZ) and bipolar disorder (BD). However, retinal microvasculature abnormalities in SCZ and BD have remained under-explored, and no study has compared this aspect of SCZ and BD till date. Retinal Images of 100 SCZ patients, BD patients, and healthy volunteers each were acquired by trained individuals using a non-mydriatic camera with a 40-degree field of view. The retinal images were quantified using a valid semi-automated method. The average of left and right eye diameters of the venules and arterioles passing through the extended zone between 0.5 and 2 disc diameters from the optic disc were calculated. The groups differed significantly with respect to average diameters of both retinal venules (P<0.001) and retinal arterioles (P<0.001), after controlling for age and sex. Both SCZ and BD patients had significantly narrower arterioles and wider venules compared to HV. There were also significant differences between SCZ and BD patients; patients with BD had narrower arterioles and wider venules. Considering the affordability and easy accessibility of the investigative procedure, retinal microvascular examination could serve as a potential screening tool to identify individuals at risk for adverse cerebrovascular events. The findings of the current study also provide a strong rationale for further systematic examination of retinal vascular abnormalities in SCZ and BD.

Role of Neuron⁻Glia Signaling in Regulation of Retinal Vascular Tone in Rats.

The interactions between neuronal, glial, and vascular cells play a key role in regulating blood flow in the retina. In the present study, we examined the role of the interactions between neuronal and glial cells in regulating the retinal vascular tone in rats upon stimulation of retinal neuronal cells by intravitreal injection of N-methyl-d-aspartic acid (NMDA). The retinal vascular response was assessed by measuring the diameter of the retinal arterioles in the in vivo fundus images. Intravitreal injection of NMDA produced retinal vasodilation that was significantly diminished following the pharmacological inhibition of nitric oxide (NO) synthase (nNOS), loss of inner retinal neurons, or intravitreal injection of glial toxins. Immunohistochemistry revealed the expression of nNOS in ganglion and calretinin-positive amacrine cells. Moreover, glial toxins significantly prevented the retinal vasodilator response induced by intravitreal injection of NOR3, an NO donor. Mechanistic analysis revealed that NO enhanced the production of vasodilatory prostanoids and epoxyeicosatrienoic acids in glial cells in a ryanodine receptor type 1-dependent manner, subsequently inducing the retinal vasodilator response. These results suggest that the NO released from stimulated neuronal cells acts as a key messenger in neuron–glia signaling, thereby causing neuronal activity-dependent and glial cell-mediated vasodilation in the retina.

High-intensity interval training modulates retinal microvascular phenotype and DNA methylation of p66Shc gene: a randomized controlled trial (EXAMIN AGE)

Impairments of retinal vessel diameter are associated with major adverse cardiovascular (CV) events. Promoter DNA methylation is a repressor of the mitochondrial adaptor p66Shc gene transcription, a key driver of ageing-induced reactive oxygen species. The study aimed to investigate whether high-intensity interval training (HIIT) affects retinal microvascular phenotype as well as p66Shc expression and oxidative stress in ageing subjects with increased CV risk from the EXAMIN AGE cohort. Eighty-four sedentary subjects (mean age 59.4 ± 7.0 years) with ≥2 CV risk factors were randomized into either a 12-week HIIT or standard physical activity recommendations. Retinal arteriolar and venular diameters were measured by use of a retinal vessel analyser. As a marker of oxidative stress plasma 3-nitrotyrosine (3-NT) level was determined by ELISA. Gene expression of p66Shc and DNA methylation were assessed in mononuclear cells by RT-qPCR and methylated-DNA capture (MethylMiner Enrichment Kit) coupled with qPCR, respectively. High-intensity interval training reduced body mass index, fat mass, low-density lipoprotein and increased muscle mass, as well as maximal oxygen uptake (VO2max). Moreover, HIIT restored microvascular phenotype by inducing retinal arteriolar widening (pre: 175 ± 14 µm vs. post: 181 ± 13 µm, P = 0.001) and venular narrowing (pre: 222 ± 14 µm vs. post: 220 ± 14 µm, P = 0.007). After HIIT, restoration of p66Shc promoter methylation (P = 0.034) reduced p66Shc gene expression (P = 0.037) and, in turn, blunted 3-NT plasma levels (P = 0.002). High-intensity interval training rescues microvascular dysfunction in ageing subjects at increased CV risk. Exercise-induced reprogramming of DNA methylation of p66Shc gene may represent a putative mechanistic link whereby exercise protects against age-related oxidative stress. ClinicalTrials.gov: NCT02796976 (https://clinicaltrials.gov/ct2/show/NCT02796976).

Propentdyopents as Heme Degradation Intermediates Constrict Mouse Cerebral Arterioles and Are Present in the Cerebrospinal Fluid of Patients With Subarachnoid Hemorrhage.

Delayed ischemic neurological deficit is the most common cause of neurological impairment and unfavorable prognosis in patients with subarachnoid hemorrhage (SAH). Despite the existence of neuroimaging modalities that depict the onset of the accompanying cerebral vasospasm, preventive and therapeutic options are limited and fail to improve outcome owing to an insufficient pathomechanistic understanding of the delayed perfusion deficit. Previous studies have suggested that BOXes (bilirubin oxidation end products), originating from released heme surrounding ruptured blood vessels, are involved in arterial vasoconstriction. Recently, isolated intermediates of oxidative bilirubin degradation, known as PDPs (propentdyopents), have been considered as potential additional effectors in the development of arterial vasoconstriction. To investigate whether PDPs and BOXes are present in hemorrhagic cerebrospinal fluid and involved in the vasoconstriction of cerebral arterioles. Via liquid chromatography/mass spectrometry, we measured increased PDP and BOX concentrations in cerebrospinal fluid of SAH patients compared with control subjects. Using differential interference contrast microscopy, we analyzed the vasoactivity of PDP isomers in vitro by monitoring the arteriolar diameter in mouse acute brain slices. We found an arteriolar constriction on application of PDPs in the concentration range that occurs in the cerebrospinal fluid of patients with SAH. By imaging arteriolar diameter changes using 2-photon microscopy in vivo, we demonstrated a short-onset vasoconstriction after intrathecal injection of either PDPs or BOXes. Using magnetic resonance imaging, we observed a long-term PDP-induced delay in cerebral perfusion. For all conditions, the arteriolar narrowing was dependent on functional big conductance potassium channels and was absent in big conductance potassium channels knockout mice. For the first time, we have quantified significantly higher concentrations of PDP and BOX isomers in the cerebrospinal fluid of patients with SAH compared to controls. The vasoconstrictive effect caused by PDPs in vitro and in vivo suggests a hitherto unrecognized pathway contributing to the pathogenesis of delayed ischemic deficit in patients with SAH.

Insights on Microvascular Flow Regulation in Microvascular Units: A Computational Modeling Study

BackgroundRegulation of RBC oxygen delivery and plasma flow is a critical function of the microcirculation. Given the complexity of microvascular networks, mathematical modeling has been an essential adjunct for understanding physiological principles. Many studies have simulated flow through branching arteriolar networks or isolated groups of capillaries, but the completed microvascular units (MVU) ‐ from terminal arteriole, through a capillary bundle, and into a post‐capillary venule ‐ has rarely been studied. Modeling this fundamental microvascular structure will help describe how capillary networks interface with the broader microcirculation and provide insight into properties of flow regulation on this scale.MethodsWe constructed an idealized MVU and applied a dual‐phase steady‐state blood flow model to solve for RBC and plasma flow. We incorporated physiologic parameters that were varied individually while keeping all of the other variables constant: (i) number of parallel capillaries in a bundle (4–10 capillaries), (ii) capillary length (50–600 micron), (iii) arteriolar inflow hematocrit (0.1–0.5), (iv) arteriolar diameter (6–18 micron), (v) venular diameter (6–18 micron), and (vi) driving pressure across the MVU. Mean and coefficient of variation (CV) were calculated for RBC flow, plasma flow, and tube hematocrit (HT) for all parallel capillaries.ResultsPlasma flow is significantly more variable than RBC flow in capillaries for all test cases in this study. Increasing the number of capillaries per bundle decreased the mean RBC and plasma flow but increased total flow through the MVU; plasma flow CV (17%–54%) and HT CV (19%–52%) increased substantially while RBC flow CV was much less affected (4%–9%). Increasing capillary length reduced mean RBC flow, plasma flow, and HT nonlinearly with an inflection point occurring at capillary lengths of 200 microns or greater. Increasing arteriolar inflow hematocrit reduced RBC flow CV (16% vs 2%) and increased plasma flow CV (26%–36%). Increases to arteriolar and venular diameter above 10 microns had little effect on the magnitude or distribution of RBC and plasma flow through the MVU. Changes to the driving pressure across the MVU had a linear effect on RBC and plasma flow with no effect on the relative distribution between capillaries.ConclusionsThis study provides insight into how the biophysical properties of the microcirculation may influence flow regulation through completed microvascular units. Pre‐ and post‐capillary microvessels appear optimized for diameters less than 10 microns. Modifications to driving pressure provide a much more straight forward method of flow regulation than alterations to vessel diameter. Future work will compare these results against in vivo capillary measurements with heterogeneous spatial geometry and explore modeling approaches for multiple interconnected MVU. Example of one idealized microvascular unit included in the study; this microvascular unit has 6 parallel capillaries with length 300 microns.imageExample of one idealized microvascular unit included in the study; this microvascular unit has 6 parallel capillaries with length 300 microns.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Inhibition of TLR4 Activation Prevents Renal Autoregulatory Impairment in Ang II Hypertensive Rats

Autoregulation by afferent arterioles regulates renal blood flow and glomerular filtration rate across widely ranging arterial pressures. Autoregulatory function is impaired in hypertension, perhaps due to release of damage associated molecular patterns that activate renal toll‐like receptor (TLR4). Autoregulatory impairment can promote hypertensive kidney injury. We hypothesize that inhibition of TLR4 activation preserves afferent arteriole autoregulatory function in Angiotensin II (AngII) hypertension.Three groups (n=4/group) of male Sprague‐Dawley rats were implanted with osmotic minipumps set to deliver: saline (0.9% NaCl) or AngII (60ng/min). Group three received AngII+anti‐TLR4 Ab (3 μg/ml/kg/day, i.p.) for 14 days. Systolic blood pressure (SBP) was assessed (days 0, 3, 7 and 13). Kidneys were harvested on day 14 for juxtamedullary nephron assessment of afferent arteriole autoregulatory function.SBP increased in the AngII and AngII+Anti‐TLR4 Ab groups compared to saline controls over the 14 days (P&lt;0.05), averaging 198 ± 11, 200 ± 8 and 135 ± 3 mmHg, respectively. Baseline arteriole diameters (100 mmHg) averaged 14 ± 0.8, 15.6 ± 1.7, and 13 ± 0.3 microns for control, AngII and AngII+Anti‐TLR4 Ab, respectively. Perfusion pressure was decreased to 65 mmHg and increased to 170 mmHg in 15 mmHg increments. At 170 mmHg, arteriole diameters decreased by 31 ± 6% and 33 ± 8% of baseline in the control and Ang II+Anti‐TLR4 Ab groups whereas the AngII group had a decline of 11.7 ± 3.7%.These data establish that autoregulatory function is Impaired in AngII hypertensive rats while it is preserved by anti‐TLR4 Ab‐treatment. These findings implicate chronic TLR4 activation as causative in the hypertensive decline in autoregulatory capability.Support or Funding InformationFunded by NHLBI; 1R25 HL115473‐01 and DK044628‐20.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Subpleural Microvascular Dysfunction in the Intact Mouse Lung in Conjunction with Increased Blood Glucose Levels, Oxidative Stress and Altered Nitric Oxide Signaling in a Model of Type‐1 Diabetes

Microvascular dilation important for distributing the blood glucose load to peripheral tissues, such as skeletal muscle, is inhibited by the loss of bioavailable nitric oxide (NO) in diabetes. The lungs could also be a target since NO signaling modulates alveolar perfusion. We tested the hypothesis that diabetes‐induced oxidative stress with subsequent over‐expression of inducible NO synthase (iNOS) and increased protein nitrosylation, leads to decreased bioavailable NO and consequently to pulmonary microvascular dysfunction. Effects of acute NO synthase (NOS) inhibition with L‐NAME on sub‐pleural pulmonary arterioles and alveoli were examined in streptozotocin‐treated C57BL/6J mice (STZ) and saline‐treated controls (Control). Microvascular changes were assessed by intra‐vital microscopy of the intact right lung in anesthetized mice (7 to 11 months old) with open chest and ventilated lungs when the lungs were statically held inflated for brief periods. Pulmonary arteriolar diameters and alveoli were measured before and after acute administration of L‐NAME, a nitric oxide synthase (NOS) inhibitor. L‐NAME significantly increased arteriolar tone in control mice (n=5). In contrast, tone decreased in STZ mice (n=5). Fixed lung tissue sections from these experiments were stained for superoxide detection by fluorescence microscopy (DHE staining) and immuno‐stained for iNOS expression and protein nitrosylation (3‐nitrotyrosine, 3‐NT) by immunohistochemistry. Superoxide formation significantly increased in STZ (22.8 ± 15.0%, p = 0.02) compared to Control (3.8 ± 1.0%) and correlated with increased blood glucose levels in STZ (372.2 ± 43.3 mg/dL) compared to Control (103.8 ± 8.8 mg/dL). Expression of iNOS also increased significantly in STZ (4.7 ± 3.1%, p = 0.009) compared to Control (0.06 ± 0.07%) as did 3‐NT formation in STZ (5.4 ± 5.5%, p = 0.008 compared to Control (0.007 ± 0.01%). Our data suggest that diabetes‐induced systemic effects alter lung endothelial signaling. Control mice had a physiological vasoconstrictor response to L‐NAME likely due to the loss of the vasodilator influence of bioavailable NO. In contrast, NOS inhibition with L‐NAME appeared to have a vasodilator effect in STZ mice by decreasing formation of a vasoconstrictor, or unmasking a vasodilator. DHE staining and 3‐NT immunoreactivity indicated increased oxidative stress related to blood glucose levels. We conclude that diabetes may adversely affect lung microvasculature by decreasing NO bioavailability and inducing oxidative injury. Altered NO‐induced responses may cause pulmonary endothelial injury and microvascular dysfunction leading to ventilation‐perfusion abnormalities that exacerbate systemic complications of diabetes.Support or Funding InformationUniversity of Louisville, School of Medicine Collaborative Enhancement GrantThis abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Visualization of the intrarenal distribution of capillary blood flow.

This study describes a modified technique to fill the renal vasculature with a silicon rubber (Microfil) compound and obtain morphologic information about the intrarenal distribution of capillary blood flow under a variety of conditions. Kidneys and cremaster muscles of rats were perfused in vivo with Microfil using a perfusion pressure equal to the animal's mean arterial pressure at body temperature. Microfil did not alter arteriolar diameter or the pattern of flow in the microcirculation of the cremaster muscle. The modified protocol reproducibly filled the renal vasculature, including; glomerular, peritubular, and vasa recta capillaries. We compared the filling of the renal circulation in control rats with that seen in animals subjected to maneuvers reported to alter the intrarenal distribution of blood flow. Infusion of angiotensin II, hypotension, volume expansion, and mannitol‐ or furosemide‐induced diuresis redistributed flow between renal cortical and medullary capillaries. The advantage of the current technique is that it provides anatomical information regarding the number, diameter, and branching patterns of capillaries in the postglomerular circulation critical in determining the intrarenal distribution of cortical and medullary blood flow.

Impact of analgesics on macro‐ and microcirculatory responses to hemorrhage

BACKGROUNDPeripheral vasoconstriction in responseto hemorrhage is critical for blood pressure compensation and vital organperfusion. Opiates and ketamine have been demonstrated to have direct vasoactive effects, but effects on peripheral vasoconstriction response to hemorrhage are unknown for these analgesics. We hypothesize that opioid(fentanyl) impairs blood pressure compensation following hemorrhage due toblunted peripheral vasoconstriction, while ketamine preserves pressure compensation and vasoconstriction.METHODSprague Dawley rats(11–13wk) were randomly assigned to saline (control), fentanyl, or ketamine‐treated groups (n = 9 for each group). Rats were anesthetized within actin and the spinotrapezius muscles were prepared for microcirculatory observation. The arcade arterioles were topically challenged with saline, fentanyl, or ketamine at concentrations relevant to analgesic doses and vascular responses were recorded. After procedurally‐challenged arteriolar diameters returned to baseline, 30% of total blood volumes were removed during a 25 min period. Ten minutes after hemorrhage, rats were treated with a single intravenous(IV) injection of an analgesic dose of fentanyl or ketamine or a comparable volume of saline. Blood pressure, respiratory rate, and arteriolar responses were recorded throughout the experiment.RESULTSBaseline parameters were not different among groups (Table 1). Topical fentanyl induced vasodilation (17 ± 2%, p &lt; 0.01)but ketamine caused vasoconstriction (−15 ± 4%; p &lt; 0.01). IV ketamine and fentanyl failed to affect blood pressure compensation compared with the control group (Figure A). Neither saline nor ketamine altered respiratory rate. However, IV fentanyl induced a prolonged suppression in respiratory rate (&gt;10 minutes, with a peak inhibition at 57 ± 8% of baseline, Figure B). A persistent and similar arteriolar constriction to hemorrhage was observed in the control and ketamine treated groups. However, this compensatory vasoconstriction was absent in the fentanyl‐treated group, which instead exhibited continuous vasodilation (peak change 42 ± 10% of baseline immediately after injection, p &lt;0.01, Figure C). While no mortality occurred with IV saline or ketamine, fentanyl caused an 18% mortality.CONCLUSIONThese results indicate that ketamine preserves, but fentanyl impairs, respiration and peripheral vasoconstrictor response to hemorrhage, although minor effects on initial compensation of systemic hemodynamics appear to be similar. The study suggests that microcirculatory responses may be more sensitive than systemichemo dynamics to predict outcomes during pain management following hemorrhage.Support or Funding InformationThis study was funded by the US Army Medical and Materiel Command, Clinical and Rehabilitative Medicine Research Program.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Neural activity drives dynamic Ca2+ signals in capillary endothelial cells that shape local brain blood flow

Brain capillaries constitute a vast, arborescent network of microscopic tubes composed of endothelial cells (ECs) that lie in close apposition to all neurons. Capillaries send long‐range electrical signals to regulate arteriolar diameter and control blood flowing into the brain, but it is unknown whether higher resolution control of blood flow exists within the capillary bed. Here, we demonstrate that capillary ECs exhibit recurrent, long‐lasting, high‐amplitude, local Ca2+ signals in vivo that depend on neuronal activity. These signals are mediated by Gq‐protein‐coupled receptors, prominently including prostaglandin E2‐induced activation of the EP1 receptor, and reflect Ca2+ release through endoplasmic reticulum IP3 receptors and Ca2+ entry through TRPV4 channels. EC Ca2+ elevation at capillary branch points relaxes overlying pericytes, which is associated with a nitric oxide‐dependent increase in local blood flow. Capillary and arteriolar ECs respond robustly to neural stimulation, suggesting coordinated Ca2+ signaling in these compartments directs blood flow to satisfy neuronal metabolic needs.Support or Funding InformationSupported by American Heart Association postdoctoral fellowships and a Scientist Development Grant (14POST20480144; 17SDG33670237 to T.A.L.; 17POST33650030 to O.F.H), the Totman Medical Research Trust (to M.T.N.), Fondation Leducq (to M.T.N.), EC Horizon 2020 (to M.T.N.), and National Institutes of Health (NIH 4P20 GM103644/4‐5 to the Vermont Centre on Behavior and Health (T.A.L); P30‐GM‐103498 to the COBRE imaging facility at the University of Vermont College of Medicine; R24‐HL‐120847 to M.I.K; P01‐HL‐095488, R01‐HL‐121706, R37‐DK‐053832 and R01‐HL‐131181 to M.T.N., and FOR2372 to G.M.K and E.K).This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.