Passive Diameter Research Articles

Knockout of Sirtuin 3 in endothelial cells impairs endothelial-dependent relaxation and myogenic response in mice.

Sirtuin 3 has been shown to regulate endothelial function and coronary flow reserve in mice. Knockout of SIRT3 reduced endothelial nitric oxide synthase expression in the mouse hearts. In this study, we investigate whether endothelial SIRT3 regulates vascular function and myogenic responses in distal intramural branches of the left anterior descending coronary artery (CA) and middle cerebral artery (MCA) of mice. Both male and female endothelial SIRT3 knockout (SIRT3ECKO) mice and control SIRT3LoxP mice were used and CA and MCA were dissected and mounted in a myograph system. The myogenic response was evaluated by measuring changes in inner diameter in response to 20 mmHg stepwise increases in intraluminal pressure in PSS (active diameter) and Ca2+-free PSS (passive diameter). Acetylcholine (Ach)-induced endothelial-dependent relaxation (EDR) and sodium nitroprusside (SNP)-induced endothelial-independent relaxation (EIR) were examined. Our results showed that the myogenic responses were significantly impaired in both the CA and MCA of SIRT3ECKO mice. Furthermore, female mice had worsened myogenic response in MCA. In CA, EDR was abolished in both male and female SIRT3ECKO mice. Intriguingly, EIR was only reduced in the female mice. In MCA, EDR was reduced in male SIRT3ECKO mice, whereas EIR was decreased in both male and female mice. Female SIRT3ECKO mice had profound dysfunction in CA, whereas male mice exhibited more dysfunction in MCA. These data revealed a sex and organ-specific role of endothelial SIRT3 in vascular function and myogenic responses. Our study suggests that endothelial SIRT3 is necessary for maintaining vascular function and blood flow autoregulation.

Influence of Passive Pre-Chamber Nozzle Diameter on Jet Ignition in a Constant-Volume Optical Engine under Varying Load and Dilution Conditions

<div>Despite the growing prominence of electrified vehicles, internal combustion engines remain essential in future transportation. This study delves into passive pre-chamber jet ignition, a leading-edge combustion technology, offering a comprehensive visualization of its operation under varying load and dilution conditions in light-duty GDI engines. Our primary objectives are to gain fundamental insights into passive pre-chamber jet ignition and subsequent main combustion processes and evaluate their response to different load and dilution conditions. We conducted experimental investigations using a light-duty, optical, single-cylinder engine equipped with three passive pre-chamber designs featuring varying nozzle diameters. Optical diagnostic imaging and heat release analysis provided critical insights. Findings reveal that as load decreases, fuel availability and flow conditions deteriorate, leading to delayed and suboptimal jet characteristics impacting main chamber ignition and combustion. Notably, at high and medium loads without dilution, the 1.2 mm-PC (smallest nozzle diameter) excels, exhibiting superior jet ignition and main combustion. This is attributed to earlier jet ejection, improved penetration, and intensified jets, all enabled by the smaller nozzle diameter. Conversely, under low load conditions, the 1.6 mm-PC (largest nozzle diameter) performs better due to enhanced scavenging and reduced pre-chamber residuals, resulting in more balanced pre-chamber combustion and jet characteristics. Furthermore, nozzle diameter significantly influences cycle-to-cycle variations, with smaller diameters enhancing jet ignition but intensifying variability. The impact of external residuals (dilution) on jet ignition performance varies with nozzle diameter, with the 1.6 mm-PC displaying less degradation and demonstrating earlier jet ejection and CA50 timing under higher dilution conditions. In summary, this research underscores the importance of scavenging and residual levels in pre-chamber design, influencing dilution tolerance, and extending possibilities for high-efficiency engines. It contributes essential insights into the behavior of passive pre-chamber jet ignition systems, facilitating their optimization for future internal combustion engines.</div>

Impact of Passive Pre-Chamber Nozzle Diameter on Jet Formation Patterns and Dilution Tolerance in a Constant-Volume Optical Engine

<div>Pre-chamber jet ignition technologies have been garnering significant interest in the internal combustion engine field, given their potential to deliver shorter burn durations, increased combustion stability, and improved dilution tolerance. However, a clear understanding of the relationship between pre-chamber geometry, operating condition, jet formation, and engine performance in light-duty gasoline injection engines remains under-explored. Moreover, research specifically focusing on high dilution levels and passive pre-chambers with optical accessibility is notably scarce. This study serves to bridge these knowledge gaps by examining the influence of passive pre-chamber nozzle diameter and dilution level on jet formation and engine performance. Utilizing a modified constant-volume gasoline direct injection engine with an optically accessible piston, we tested three passive pre-chambers with nozzle diameters of 1.2, 1.4, and 1.6 mm, while nitrogen dilution varied from 0 to 20%. With the help of high-speed imaging, we captured pre-chamber jet formations and subsequent flame propagation within the main chamber. Our novel findings reveal that asymmetric temporal and spatial jet formation patterns arising from pre-chambers significantly impact engine performance. The larger-nozzle-diameter pre-chambers exhibited the least variation in jet formation due to their improved scavenging and main mixture filling processes, but had the slowest jet velocity and lowest jet penetration depth. At no dilution condition, the 1.2 mm-PC demonstrated superior performance attributed to higher pressure build-up in the pre-chamber, resulting in accelerated jet velocity and increased jet penetration depth. However, at high dilution condition, the 1.6 mm-PC performed better, highlighting the importance of scavenging and symmetry jet formation. This study emphasizes the importance of carefully selecting the pre-chamber nozzle diameter, based on the engine’s operating conditions, to achieve an optimal and balanced configuration that can improve both jet formation and jet characteristics, as well as scavenging.</div>

Effect of passive pre-chamber orifice diameter on the methane combustion process in an optically accessible SI engine

Due to its potential to extend the lean limit or overcome knock-limited conditions on spark-ignited (SI) engines, the pre-chamber spark-ignition (PCSI) concept has gained attention as an efficient alternative to the conventional ignition architecture. Nevertheless, especially in engine-like conditions, the effect of the main geometrical parameters on combustion development is still not fully understood and might be a hindrance to the use of this technology. In this sense, the current study aims to evaluate the effect of the orifice diameter on the jet characteristics and main chamber combustion of a novel passive pre-chamber in an optically accessible single-cylinder SI engine, as well as to compare the PCSI with the typical SI ignition method. High-speed broadband chemiluminescence imaging was used to track the jet penetration and flame front propagation of three mixture compositions at various spark timings (ST). Additionally, based on the in-cylinder pressure, a heat-released analysis was performed to assess the overall combustion process. When compared with the typical SI, the pre-chamber concept presented a higher equivalent flame front velocity, which is also corroborated by the higher in-cylinder pressure rise rate and rate of heat released. For all mixtures tested, the 1.2 mm orifice diameter PC presented the shortest flame development angle (crank angle interval between ST and 10 % of mass fraction burned in the MC), followed by 1.5 and lastly 1.0 mm. When comparing different STs, the shortest flame development angle occurred at MBT condition. Despite the highest flame development angle, the PC 1.0 mm case presented the lowest main chamber combustion duration (CA10-90), which increases as the orifice diameter is increased.

The role of nitric oxide in flow-induced and myogenic responses in 1A, 2A, and 3A branches of the porcine middle cerebral artery.

Myogenic and flow-induced reactivity contribute to cerebral autoregulation, with potentially divergent roles for smaller versus larger arteries. The present study tested the hypotheses that compared with first-order (1A) branches of the middle cerebral artery, second- and third-order branches (2A and 3A, respectively) exhibit greater myogenic reactivity but reduced flow-induced constriction. Furthermore, nitric oxide synthase (NOS) inhibition may amplify myogenic reactivity and abolish instances of flow-induced dilation. Isolated porcine cerebral arteries mounted in a pressure myograph were exposed to incremental increases in intraluminal pressure (40-120 mmHg; n = 41) or flow (1-1,170 µL/min; n = 31). Intraluminal flows were adjusted to achieve 5, 10, 20, and 40 dyn/cm2 of wall shear stress at 60 mmHg. Myogenic tone was greater in 3A versus 1A arteries (P < 0.05). There was an inverse relationship between myogenic reactivity and passive arterial diameter (P < 0.01). NOS inhibition increased basal tone to a lesser extent in 3A versus 1A arteries (P < 0.01) but did not influence myogenic reactivity (P = 0.49). Increasing flow decreased luminal diameter (P ≤ 0.01), with increased vasoconstriction at 10-40 dyn/cm2 of shear stress (P < 0.01). However, relative responses were similar between 1A, 2A, and 3A arteries (P = 0.40) with and without NOS inhibition conditions (P ≥ 0.29). Whereas NOS inhibition increases basal myogenic tone, and myogenic reactivity was less in smaller versus larger arteries (range = ∼100-550 µM), neither NOS inhibition nor luminal diameter influences flow-induced constriction in porcine cerebral arteries.NEW & NOTEWORTHY This study demonstrated size-dependent heterogeneity in myogenic reactivity in porcine cerebral arteries. Smaller branches of the middle cerebral artery exhibited increased myogenic reactivity, but attenuated NOS-dependent increases in myogenic tone compared with larger branches. Flow-dependent regulation does not exhibit the same variation; diameter-independent flow-induced vasoconstrictions occur across all branch orders and are not affected by NOS inhibition. Conceptually, flow-induced vasoconstriction contributes to cerebral autoregulation, particularly in larger arteries with low myogenic tone.

Sirt1 overexpression attenuates Western-style diet-induced aortic stiffening in mice.

Increased arterial stiffness is a cardiovascular disease risk factor in the setting of advancing age and Western diet (WD) induced obesity. Increases in large artery stiffness, as measured by pulse wave velocity (PWV), occur within 8 weeks of WD feeding in mice. Sirtuin‐1 (Sirt1), a NAD‐dependent deacetylase, regulates cellular metabolic activity and activation of this protein has been associated with vasoprotection in aged mice. The aim of the study was to elucidate the effect of global Sirt1 overexpression (Sirttg) on WD‐induced arterial stiffening. Sirt1 overexpression did not influence PWV in normal chow (NC) fed mice. However, PWV was higher in wild‐type (WT) mice (p < 0.04), but not in Sirttg mice, after 12 weeks of WD and this effect was independent of changes in blood pressure or the passive pressure diameter relation in the carotid artery. Overexpression of Sirt1 was associated with lower collagen and higher elastin mRNA expression in the aorta of WD fed mice (both p < 0.05). Although MMP2 and MMP3 mRNA were both upregulated in WT mice after WD (both p < 0.05), this effect was reversed in Sirttg mice compared to WT mice fed WD (both p < 0.05). Surprisingly, histologically assessed collagen and elastin quality were unchanged in the aortas of WT or Sirttg mice after WD. However, Sirttg mice were protected from WD‐induced glucose intolerance, although there was no difference in insulin tolerance between groups. These findings demonstrate a vasoprotective effect of Sirt1 overexpression that limits the increase in arterial stiffness in response to consumption of a WD.

The Effect of Pregnancy Status on Rat Main Uterine Artery and Radial Uterine Artery Structure and Function

BackgroundHealthy pregnancy is associated with remodeling of the maternal uterine vasculature to meet the metabolic demands of the developing fetus. In contrast to the systemic circulation during pregnancy, it has been suggested that pregnancy decreases radial uterine artery (RUA) distensibility, potentially persisting throughout the postpartum period. The intent of this study is to compare RUA and main uterine artery (MUA) during late pregnancy and the postpartum period to determine whether pregnancy‐related changes in distensibility is similar in both large and small uterine vessels.MethodsMUAs and RUAs from NP (n=7‐9), LP (gestational age: 21±1 d, n=6‐8), and 30±1 days postpartum (PP30; n=4‐6) Sprague‐Dawley rats were isolated, cleaned of connective tissue, cut into 8mm segments, and cannulated in an arteriograph chamber to assess vascular reactivity to the addition of 60 mM KCl and phenylephrine (PE, 1 µM). In addition, passive mechanical properties such as lumen diameter, wall thickness, distensibility and arterial stress/strain were assessed at intraluminal pressures ranging from 10mm Hg to 140mm Hg. Data were analyzed using one‐way ANOVA or two‐way ANOVA. Data were considered significant at P&lt;0.05.ResultsK+‐ induced constriction was similar in RUAs and MUAs from NP, LP, and PP30 rats. PE‐induced constrictions were similar at all pregnancy states in RUAs. In contrast, PE‐induced constriction in LP MUA was greater than NP MUA (P&lt;0.05) and PP30 MUA (P&lt;0.01). Passive LP RUA lumen diameter was greater than PP30 RUA (P&lt;0.05) and trended toward significance in NP RUA (P&lt;0.07). Passive NP MUA lumen diameters were smaller than MUA diameters from LP (P&lt;0.05) and PP30 (P&lt;0.05) rats. There was no difference in arterial wall thickness between NP, LP and PP30 MUAs (P=NS) and NP, LP and PP30 RUAs (P=NS). Distensibility in NP RUA was greater than PP30 RUAs (P&lt;0.05), but there was no statistical difference in distensibility between LP RUA and PP30 RUAs. There was no difference in distensibility in MUAs at all pregnancy states. Stress/strain relationships unmasked vascular remodeling in both RUAs and MUAs. There was a significantly greater leftward shift in stress/strain values in RUAs from PP30 rats than RUAs from LP (P&lt;0.05) and NP (P&lt;0.05) rats. Furthermore, stress/strain values from LP RUAs were different than RUAs from PP30 (P&lt;0.05) and NP (P&lt;0.05) animals. Similar to RUA, the leftward shift in stress/strain values from PP30 MUA were statistically greater than MUA from LP and NP animals.ConclusionsThese preliminary data suggest that significant vascular remodeling occurs with pregnancy which persists 30 days post parturition. Additional studies need to be completed to determine how multiple pregnancies may alter RUA and MUA structure and function.

Wildfire Smoke Observations in the Western United States from the Airborne Wyoming Cloud Lidar during the BB-FLUX Project. Part II: Vertical Structure and Plume Injection Height

Abstract The western U.S. wildfire smoke plumes observed by the upward-pointing Wyoming Cloud Lidar (WCL) during the Biomass Burning Fluxes of Trace Gases and Aerosols (BB-FLUX) project are investigated in a two-part paper. Part II here presents the reconstructed vertical structures of seven plumes from airborne WCL measurements. The vertical structures evident in the fire plume cross sections, supported by in situ measurements, showed that the fire plumes had distinct macrophysical and microphysical properties, which are closely related to the plume transport, fire emission intensity, and thermodynamic structure in the boundary layer. All plumes had an injection layer between 2.8 and 4.0 km above mean sea level, which is generally below the identified boundary layer top height. Plumes that transported upward out of the boundary layer, such as the Rabbit Foot and Pole Creek fires, formed a higher plume at around 5.5 km. The largest and highest Pole Creek fire plume was transported farthest and was sampled by University of Wyoming King Air aircraft at 170 km, or 2.3 h, downwind. It was associated with the warmest, driest, deepest boundary layer and the highest wind speed and turbulence. The Watson Creek fire plume intensified in the afternoon with stronger CO emission and larger smoke plume height than in the morning, indicating a fire diurnal cycle, but some fire plumes did not intensify in the afternoon. There were pockets of relatively large irregular aerosol particles at the tops of plumes from active fires. In less-active fire plumes, the WCL depolarization ratio and passive cavity aerosol spectrometer probe mass mean diameter maximized at a height that was low in the plume.

Modeling acute and chronic vascular responses to a major arterial occlusion.

To incorporate chronic vascular adaptations into a mathematical model of the rat hindlimb to simulate flow restoration following total occlusion of the femoral artery. A vascular wall mechanics model is used to simulate acute and chronic vascular adaptations in the collateral arteries and collateral-dependent arterioles of the rat hindlimb. On an acute timeframe, the vascular tone of collateral arteries and distal arterioles is determined by responses to pressure, shear stress, and metabolic demand. On a chronic timeframe, sustained dilation of arteries and arterioles induces outward vessel remodeling represented by increased passive vessel diameter (arteriogenesis), and low venous oxygen saturation levels induce the growth of new capillaries represented by increased capillary number (angiogenesis). The model predicts that flow compensation to an occlusion is enhanced primarily by arteriogenesis of the collateral arteries on a chronic time frame. Blood flow autoregulation is predicted to be disrupted and to occur for higher pressure values following femoral arterial occlusion. Structural adaptation of the vasculature allows for increased blood flow to the collateral-dependent region after occlusion. Although flow is still below pre-occlusion levels, model predictions indicate that interventions which enhance collateral arteriogenesis would have the greatest potential for restoring flow.

Prolonged mechanical ventilation increases diaphragm arteriole circumferential stretch without changes in stress/stretch: Implications for the pathogenesis of ventilator-induced diaphragm dysfunction.

Prolonged mechanical ventilation (MV; ≥6h) results in large, time-dependent reductions in diaphragmatic blood flow and shear stress. We tested the hypothesis that MV would impair the structural and material properties (ie, increased stress/stretch relation and/or circumferential stretch) of first-order arterioles (1A) from the medial costal diaphragm. Shear stress was estimated from isolated arterioles and prior blood flow data from the diaphragm during spontaneous breathing (SB) and prolonged MV (6h MV). Thereafter, female Sprague-Dawley rats (~5months) were randomly divided into two groups, SB (n=6) and 6h MV (n=6). Following SB and 6h MV, 1A medial costal diaphragm arterioles were isolated, cannulated, and subjected to stepwise (0-140cmH2 O) increases in intraluminal pressure in calcium-free Ringer's solution. Inner diameter and wall thickness were measured at each pressure step and used to calculate wall:lumen ratio, Cauchy-stress, and circumferential stretch. Compared to SB, there was a ~90% reduction in arteriolar shear stress with prolonged MV (9±2 vs 78±20dynes/cm2 ; p≤.05). In the unloaded condition (0cmH2 O), the arteriolar intraluminal diameter was reduced (37±8 vs 79±13μm) and wall:lumen ratio was increased (120±18 vs 46±10%) compared to SB (p≤.05). There were no differences in the passive diameter responses or the circumferential stress/stretch relationship between groups (p>.05), but at each pressure step, circumferential stretch was increased with 6h MV vs SB (p≤.05). During prolonged MV, medial costal diaphragm arteriolar shear stress is severely diminished. Despite no change in the material behavior (stress/stretch), prolonged MV resulted in altered structural and mechanical properties (ie, elevated circumferential stretch) of medial costal diaphragm arterioles. This provides important novel mechanistic insights into the impaired diaphragm blood flow capacity and vascular dysfunction following prolonged MV.

Myogenic Tone in Peripheral Resistance Arteries and Arterioles: The Pressure Is On!

Resistance arteries and downstream arterioles in the peripheral microcirculation contribute substantially to peripheral vascular resistance, control of blood pressure, the distribution of blood flow to and within tissues, capillary pressure, and microvascular fluid exchange. A hall-mark feature of these vessels is myogenic tone. This pressure-induced, steady-state level of vascular smooth muscle activity maintains arteriolar and resistance artery internal diameter at 50–80% of their maximum passive diameter providing these vessels with the ability to dilate, reducing vascular resistance, and increasing blood flow, or constrict to produce the opposite effect. Despite the central importance of resistance artery and arteriolar myogenic tone in cardiovascular physiology and pathophysiology, our understanding of signaling pathways underlying this key microvascular property remains incomplete. This brief review will present our current understanding of the multiple mechanisms that appear to underlie myogenic tone, including the roles played by G-protein-coupled receptors, a variety of ion channels, and several kinases that have been linked to pressure-induced, steady-state activity of vascular smooth muscle cells (VSMCs) in the wall of resistance arteries and arterioles. Emphasis will be placed on the portions of the signaling pathways underlying myogenic tone for which there is lack of consensus in the literature and areas where our understanding is clearly incomplete.

Deficiency in CD4 T Cells Leads to Enhanced Postpartum Internal Carotid Artery Vasoconstriction in Mice: The Role of Nitric Oxide.

The risk of postpartum (PP) stroke is increased in complicated pregnancies. Deficiency in CD4 T cell subsets is associated with preeclampsia and may contribute to PP vascular disease, including internal carotid artery (ICA) stenosis and stroke. We hypothesized that CD4 T cell deficiency in pregnancy would result in ICA dysregulation, including enhanced ICA vasoconstriction. We characterized the function, mechanical behavior, and structure of ICAs from C57BL/6 (WT) and CD4 deficient (CD4KO) mice, and assessed the role of NO in the control of ICA function at pre-conception and PP. WT and CD4KO mice were housed under pathogen-free conditions, mated to same-strain males, and allowed to litter or left virgin. At 3 days or 4 weeks PP, mice were euthanized. The responses to phenylephrine (PE), high K+ and acetylcholine (ACh) were assessed in pressurized ICAs before and after NOS inhibition. Passive lumen diameters were measured at 3–140 mmHg. eNOS and iNOS expression as well as the presence of T cells were evaluated by immunohistochemistry. Constriction of WT ICAs to PE was not modified PP. In contrast, responses to PE were significantly increased in ICAs from PP as compared to virgin CD4KO mice. Constriction to high K+ was not enhanced PP. ICAs from WT and CD4KO mice were equally sensitive to ACh with a significant rightward shift of dose-response curves after L-NNA treatment. NOS inhibition enhanced PE constriction of ICAs from WT virgin and PP mice. Although a similar effect was detected in ICAs of virgin CD4KO mice, no such changes were observed in vessels from PP CD4KO mice. Passive arterial distensibility at physiological levels of pressure was not modified at PP. ICA diameters were significantly increased in PP with no change in vascular wall thickness. Comparison of eNOS expression in virgin, 3 days and 4 weeks PP revealed a reduced expression in ICA from CD4 KO vs. WT PP vessels which reached significance at 4 weeks PP. iNos expression was similar and decreased over the PP period in vessels from WT and CD4KO mice. Dysregulation of the CD4 T cell population in pregnancy may make ICA vulnerable to vasospasm due to decreased NO-dependent control of ICA constriction. This may lead to cerebral hypoperfusion and increase the risk of maternal PP stroke.

Investigation of Sphingosine‐1‐Phosphate‐induced Vasodilation in the Human Microvasculature

The sphingolipid sphingosine-1-phosphate (S1P) has emerged as a regulator of microvascular tone in animals, however its role in the human microcirculation remains unknown. Pre-clinical studies suggest that S1P-induced activation of two endothelial-specific receptors, S1PR1 and S1PR3,elicits nitric-oxide (NO)-mediated vasodilation. As opposed to S1PR1, the S1PR3 pathway also activates NADPH oxidase (NOX) to produce reactive oxygen species (ROS). We therefore hypothesized that S1P induces vasodilation in the human microvasculature through activation of S1PR1 and S1PR3 in both a ROS-independent and ROS-dependent manner, respectively. Human microvessels (100-200µm in diameter) were prepared for videomicroscopy. Following equilibration, arterioles were pre-constricted with endothelin-1 to 30-70% of their passive diameters. Luminal diameter was measured and recorded in regular intervals (1 min) in response to increasing concentrations of S1P (10-12 to 10-6 M) in the presence or absence of the S1PR1 receptor antagonist W146 (10-5M), S1PR3 antagonist CAY10444 (10-5 M), nitric oxide synthase inhibitor Nω-nitro-ʟ-arginine (L-NAME, 10-4 M), NO scavenger 2-4-carboxyphenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (c-PTIO, 10-4 M), polyethylene glycol-catalase (peg-Cat, 500U/ml), NADPH oxidase inhibitor apocynin (3x10-4 M), NOX-2 inhibitor GSK2795039 (10-6 M) or the NOX-4 inhibitor GKT137831 (10−6 M). S1P induced vasodilation in a dose-responsive manner with a maximum dilation of 56.5%±4.9, n=12 (mean±SEM). Dilation was abolished during inhibition of S1PR1 (1.5%±5.2, n=4) and was reduced during inhibition of S1PR3 (19.7%±8.7, n=6). Both L-NAME and c-PTIO inhibited S1P-induced dilation (13.0%±7.5, n=4 and 11.2%±3.3, n=4, respectively). Interestingly, dilation was nearly completely inhibited by peg-Cat (11%±6.6, n=4), apocynin (12.5%±4.4, n=3) and the NOX-4 inhibitor (7.2%±3.1, n=4). Dilation was also partly reduced during inhibition of NOX-2 (25.6%±7.8, n=4). These data suggest that S1P-induced dilation occurs through activation of S1PR1 and S1PR3 through formation of NO and NOX-4-generated H2O2. These translational studies highlight the inter-species variation observed in vascular signaling and provide insight into the mechanism by which S1P regulates microvascular resistance in humans.

Upregulation of Epithelial Na + Channel Beta Subunit in Isolated Mouse Middle Cerebral Artery Enhances Pressure‐Induced Constriction

Pressure-induced constriction (PIC), also referred to as myogenic constriction, is an intrinsic response to the vascular smooth muscle cell (VSMC) of small arteries and arterioles. The response is mechano-dependent and initiated by intraluminal pressure-induced VSMC stretch. While numerous molecules are required for the overall signaling response, our laboratories have focused on the role of Degenerin (Deg) proteins, such as Epithelial Na+Channel (ENaC), because of their close evolutionary link to known mechanosensors in the nematode. Loss of function phenotypes, using broad spectrum pharmacological inhibition and specific gene silencing, have been demonstrated in cerebral arteries. However, a gain of function phenotype has not been shown. Demonstration of a gain of function phenotype is critical to establishing a role for loss of vascular degenerin function in certain diseases, such as pre-eclampsia. Thus, the aim of this study was to determine if upregulation of full-length βENaC in the isolated middle cerebral artery (MCA) enhances the PIC response. To address this aim, MCA segments were dissected from mature, female mice (24 weeks old, mixed genetic background) and transiently transfected with βENaC enhanced green fluorescent protein (EGFP) fusion vector (βENaC-EGFP, n=5) or with EGFP alone (EGFP, n=5) using Lipofectamine 3000 (Thermo Fisher Scientific) using a 1:1 ratio. Vessel segments were incubated for 18 hours at 37 °C and 5% CO2, then pressurized in a pressure-flow myograph system with physiological salt solution. Responses to KCl (20-80 mM), phenylephrine (PE, 10-7-10-4 M), and active (+Ca2+) and passive (-Ca2+) diameters measured under graded pressure steps (15-90 mm Hg, 15 mm Hg increments, 5 min) were determined to assess vasoconstriction to depolarizing and α-adrenergic agonists and intraluminal pressure, respectively. Data were analyzed using repeated measures ANOVA. MCA vasoconstrictor responses to KCl (80 mM, 30.3±2.2% vs 34.3±4.2%, main effect of treatment p=0.55) and PE (10-4 M, 40.3±4.0% vs 35.6.0±3.1%, main effect of treatment p=0.73) were identical in βENaC-EGFP and EGFP transfected segments, respectively. Circumferential stress/strain, wall thickness and wall-to-lumen ratio were also similar. In contrast, PIC responses were greater in βENaC-EGFP group at >30 mm Hg (main effect of treatment p=0.0015). Peak myogenic tone was nearly 2 fold greater in βENaC-EGFP treated segments (11.6±0.4% vs 6.3±0.4% at 75 mmHg, p=0.0006). These data confirm previous findings that βENaC is an important mediator of the PIC response. Moreover, they provide proof-of-concept that upregulating βENaC can potentially improve PIC responses in cerebral vessels and will allow us to test the hypothesis that downregulation of vascular βENaC in inflammatory conditions, such as preeclampsia, contributes to cerebrovascular dysfunction.

Twisted tapered plastic optical fibers for continuous liquid level sensing

Abstract A low-cost liquid level sensor capable of continuous liquid level sensing is proposed in this work. The sensor is based on twisted tapered plastic optical fibers (POFs) which is fabricated by twisting the tapered POFs around each other. The tapered structure could enhance the evanescent field and the light transmission from one POF to the other. The changes of liquid level can lead to the variations of light intensity at two output ends of the probe and by monitoring the changes of the coupling ratio, the liquid level can be measured. Experimental results show that a linear response with the sensitivity of 0.65%/mm and response time of 3.2 s is obtained when the probe is with active fiber diameter of 150 µm and the passive fiber diameter of 250 µm. In addition, the influences of tapered POFs diameters, the liquid refractive index and the temperature on the sensing performance are investigated, and the repeatability and the dynamic performance for the probe are also tested.

Impact of Acute and Chronic Hypertension on Changes in Pial Collateral Tone In Vivo During Transient Ischemia.

We investigated vasoconstrictive responses of pial collaterals in vivo at baseline and during transient middle cerebral artery occlusion during chronic hypertension. A cranial window was used to measure diameter of leptomeningeal anastomoses (pial collaterals) in male Wistar (n=8) and spontaneously hypertensive rats (SHRs; n=8) using video dimensional analysis. Middle cerebral artery occlusion was induced by remote filament for 2 hours with 2 hours reperfusion. Phenylephrine was infused during ischemia as a pressor therapy. Active diameters of pial collaterals were significantly smaller in SHRs versus Wistar (14.1±1.5 versus 21.6±2.8 µm; P<0.01); however, passive diameters were similar (25.0±2.9 versus 25.0±2.6 µm; P>0.05). Basal tone of pial collaterals before occlusion was 42±5% in SHRs versus 15±4% in Wistar (P<0.01). Tone decreased in both Wistar and SHRs during occlusion but remained higher in SHRs (9±2% versus 29±4%; P<0.05). Phenylephrine increased blood pressure in both groups but had little effect on leptomeningeal anastomoses diameters. Reperfusion caused vasoconstriction of pial collaterals, increasing tone from 8±1% to 20±5% in Wistar and 29±5% to 44±5% in SHRs (P<0.01). Higher tone in pial collaterals from SHRs basally and during occlusion/reperfusion could limit flow to the penumbra and promote evolution of infarction. Sustained elevated tone of pial collaterals from SHRs with phenylephrine suggests pressor therapy may not be appropriate during chronic hypertension.

Traumatic Brain Injury Impairs Flow‐Dependent Constrictions of Isolated Rat Middle Cerebral Arteries, Primarily by Interfering with the Flow Sensing Mechanisms

BackgroundTraumatic brain injury (TBI) is a major health problem worldwide due to its high mortality (35–40%), and morbidity (headache, brain edema, cognitive, behavioral, and communicative disabilities). Previously we have shown that mechanotransductions of two hemodynamic factors, pressure and flow are importantly involved in the autoregulation of cerebral blood flow, which may become inefficient after TBI. Indeed, previously we have shown that TBI diminishes pressure‐induced myogenic constriction of middle cerebral arteries (MCA). In the present study we hypothesized that TBI effects also flow‐induced constrictor response of MCA.MethodsTBI was induced in anaesthetized rat by Marmarou’s weight drop model, then MCA was isolated and transferred into pressure‐flow chamber. Inflow and outflow pressures were controlled and measured. The internal diameter was continuously measured by a videomicroscopy equipped with a microangiometer and recorded digitally by PowerLab system (AD Instruments). Data are mean±SEM.ResultsThe active (242,2±6,1 μm) and passive (277,9±8,8) diameters (p&lt;0.05) of isolated MCAs of control rats (n=39) indicate that a substantial myogenic tone developed in response to pressure (80 mmHg: Δ−35,7 ±2,7 μm, p&lt;0.05). Arachidonic acid (AA) ‐ after initial dilations (+6±3 and +9±2,5 μm) ‐ elicited dose dependent constrictions (−9±2,1 and −20±3,2 μm) of MCA of control rats. Step increases in flow elicited gradual constrictions of MCA of control rats (from max.: 229,3±6,6 to 191±6 μm, Δ−38,3 ±0,6 μm, p&lt;0.05), which was eliminated after TBI (from 227,3±14,1 to 227,4±13,3 μm). U46619, a thromboxane A2 (TXA2) / prostaglandin H2 (PGH2) receptor (TP receptor) agonist elicited similar constrictions of MCA of control and TBI rats (max.: Δ−66,1 ±0,7 μm vs. Δ−49 ±4 μm) rats, which were eliminated by SQ 29,548 a TP receptor antagonist. CYP‐450 metabolite 20‐HETE elicited similar constrictions of MCA in control (Δ−18 ±0,9 μm and TBI rats (Δ−15 ±0,1 μm) which were eliminated by HET0016, an inhibitor of CYP‐450. Paxilline (an inhibitor of potassium channel blocker) inhibited flow‐induced constrictions of MCA of control (max.: Δ−37,5 ±3 μm vs. max.: Δ−2,8 ±1 μm, p&lt;0.05), whereas did not affect the diameters of MCA after TBI (max.: Δ−0,1 ±1,6 μm vs. Δ−2,5 ±3 μm).ConclusionsThese findings suggest that 1) flow‐induced constrictor response of MCA depends on AA‐metabolites acting on TP receptors, 2) constrictor responses to TP agonists remain intact after TBI, 3) thus TBI interferes primarily with the flow sensing mechanisms of the vascular wall, which 4) likely leads to diminished autoregulation of cerebral blood flow.Support or Funding InformationScientific Excellence Program 2019., at the University of Physical Education, Innovation and Technology Ministry, Hungary TUDFO/51757/2019‐ITM and Higher Education Institutional Excellence Program at Semmelweis University and the National Bionika Program ED_17‐1‐2017‐0009, Hungary, and the University of Pecs within the framework of the 5th. thematic programme, National Research Development and Innovation Office NKFI‐FK123798.

Hyperglycemia-induced transcriptional regulation of ROCK1 and TGM2 expression is involved in small artery remodeling in obese diabetic Göttingen Minipigs.

Obesity and diabetes in humans are associated with hypertrophic remodeling and increased media:lumen ratio of small resistance arteries, which is an independent predictor of cardiovascular events. In order to minimize increases in media:lumen ratio, hypertrophic remodeling should be accompanied by outward remodeling. We aimed to investigate the mechanisms of structural remodeling in small pial arteries (PAs) and terminal mesenteric arteries (TMAs) from obese Göttingen Minipigs with or without diabetes. Göttingen Minipigs received either control diet (lean control (LC)), high fat/high fructose/high cholesterol diet (FFC), or FFC diet with streptozotocin (STZ)-induced diabetes (FFC/STZ) for 13 months. At the end of the study (20 months), we assessed body weight, fasting plasma biochemistry, passive vessel dimensions, mRNA expression (matrix metallopeptidases 2/9 (MMP2, MMP9), tissue inhibitor of metallopeptidase 1 (TIMP1), transglutaminase 2 (TGM2), Rho-kinase 1 (ROCK1), TGFβ-receptor 2 (TGFBR2), and IGF1-receptor (IGFR1) genes), and immunofluorescence in PAs and TMAs. We performed multiple linear correlation analyses using plasma values, structural data, and gene expression data. We detected outward hypertrophic remodeling in TMAs and hypertrophic remodeling in PAs from FFC/STZ animals. ROCK1 and TGM2 genes were up-regulated in PAs and TMAs from the FFC/STZ group. Passive lumen diameter (PLD) of TMAs was correlated with plasma values of glucose (GLU), fructosamine (FRA), total cholesterol (TC), and triglycerides (TGs). ROCK1 and TGM2 expressions in TMAs were correlated with PLD, plasma GLU, fructosamine, and TC. ROCK1 and TGM2 proteins were immunolocalized in the media of PAs and TMAs, and their fluorescence levels were increased in the FFC/STZ group. Hyperglycemia/hyperlipidemia is involved in regulation of ROCK1 and TGM2 expression leading to outward remodeling of small resistance arteries in obese diabetic Göttingen Minipigs.

Shear Stress Attenuates Inward Remodeling in Cultured Mouse Thoracodorsal Arteries in an eNOS-Dependent, but Not Hemodynamic Manner, and Increases Cx37 Expression

Background: Arteries chronically constricted in culture remodel to smaller diameters. Conversely, elevated luminal shear stress (SS) promotes outward remodeling of arteries in vivo and prevents inward remodeling in culture in a nitric oxide synthase (NOS)-dependent manner. Objectives: To determine whether SS-induced prevention of inward remodeling in cultured arteries is specifically eNOS-dependent and requires dilation, and whether SS alters the expression of eNOS and other genes potentially involved in remodeling. Methods: Female mouse thoracodorsal arteries were cannulated, pressurized to 80 mm Hg, and cultured for 2 days with low SS (<7 dyn/cm²), high SS (≥15 dyn/cm²), high SS + L-NAME (NOS inhibitor, 10^–4 M), or high SS in arteries from eNOS–/– mice. In separate arteries cultured 1 day with low or high SS, eNOS and connexin (Cx) 37, Cx40, and Cx43 mRNA were assessed with real-time PCR. Results: High SS caused little change in passive diameters after culture (–4.7 ± 2.0%), which was less than low SS (–18.9 ± 1.4%; p < 0.0001), high SS eNOS–/– (–18.0 ± 1.5; p < 0.001), or high SS + L-NAME (–12.0 ± 0.6%; nonsignificant) despite similar constriction during culture. Cx37 mRNA expression was increased (p < 0.05) with high SS, but other gene levels were not different. Conclusions: eNOS is involved in SS-induced prevention of inward remodeling in cultured small arteries. This effect does not require NO-mediated dilation. SS increased Cx37.

Abstract 625: Mixed Lineage Kinase 3 Regulates Blood Pressure Through Kinase Independent Effects in the Vasculature

Background: Mixed lineage kinase 3 (MLK3) opposes pathologic cardiac remodeling, but its role in blood pressure (BP) has not been studied. MLK3 activates JNK signaling through kinase-dependent effects, and opposes RhoA activation through kinase-independent mechanisms, but the relevance of these mechanisms to BP is unknown. We investigated the effect of genetic deletion of MLK3 on BP. Methods and Results: Using ambulatory telemetric monitoring in 3 month old male mice, MLK3 -/- mice had significant hypertension compared to wild type (WT) littermates (WT systolic BP 121 ± 2 mmHg, MLK3-/- 162 ± 5 mmHg; n=3; p&lt;0.05). The MLK3 kinase inhibitor URMC-099 (10 mg/kg IP) did not affect BP in WT mice. By contrast, inhibition of downstream RhoA dependent Kinase (ROCK) with Y-27632 (15 mg/kg) fully normalized BP in MLK3 -/- mice (SBP WT baseline 126 ± 2 mmHg; WT ROCK inhibitor 94 ± 2 mmHg; MLK-/- baseline 163 ±6 mmHg; MLK3 -/- ROCK inhibitor 94 ± 12 mmHg; n=5 WT, 9 MLK3-/-). Aortic pulse wave velocity was elevated in MLK-/- mice (2.7 ± 0.1 mm/ms WT vs 3.6 ± 0.2 mm/ms MLK3-/-; p&lt;0.05) indicating increased aortic stiffness. Pressure myography in mesenteric resistance arterioles of MLK3 -/- mice revealed reduced distensibility compared to WT. Both pressure myography and direct histological measurement in resistance arterioles demonstrated reduced passive luminal diameter but preserved wall cross sectional area in MLK3-/- arterioles, indicating eutrophic remodeling. Compared with dispersed aortic smooth muscle cells from WT littermates, MLK3 -/- cells had increased actin stress fiber accumulation and cell area. Summary and Conclusions: These data demonstrate that MLK3 deletion leads to hypertension with increased arterial stiffness, reduced distensibility and eutrophic remodeling of resistance vessels, but retained BP responsiveness to downstream ROCK inhibition. Together with previous work, these findings support that MLK3 modulates cardiac remodeling through a kinase dependent mechanism while modulating blood pressure through kinase-independent effects. Because hypotension limits many heart failure therapies, delineating vascular versus cardiac mechanisms of MLK3 signaling has the potential to suggest novel approaches to heart failure treatment.