Alterations in bovine endothelial histidine decarboxylase activity following exposure to shearing stresses

Endothelial cell injury produced by elevated intravascular stresses represents a causative factor in atherogenesis. Of the various hemodynamic stresses, those imposed by shear have been particularly implicated. Since it is well established that tissue histamine synthesis increases following various forms of injury, and since endothelial histamine synthesis is considerably greater than that of other wall components, the histidine decarboxylase (HD) activity of primary cultures of bovine endothelium following 1.5 hr exposure to various shearing stress intensities has been examined. Results indicate that with respect to paired, nonstressed control cultures, endothelial cell HD activity increases 2.8-, 2.3-, and 3.7-fold when subjected to mean shearing stresses of 2.8, 4.6, and 6.2 dynes/cm², respectively. These data indicate endothelial histamine synthesis is extremely sensitive to shearing stress exposure, and suggest this enzyme system may represent an enzymatic coupler between hemodynamic stresses and subsequent permeability alterations.     

Hemodynamic modulation of monocytic cell adherence to vascular endothelium

Hemodynamic shear stress is hypothesized to contribute to the localization of atherosclerotic plaques to certain arterial sites. Monocyte recruitment to these sites is an early event in atherogenesis. To determine the possible mechanisms by which shear stress modulates monocyte adhesionin vivo, studies of human monocytic cell adherence to endothelium were conducted under different shear conditions in a parallel-plate flow chamber. The number of monocytes capable of developing firm adhesive contacts with endothelium decreased as shear stress-induced drag forces increased over the range of 0.5 to 30 dynes/cm². The number of adherent monocytic cells at a given shear stress was highly dependent on the activation state of the endothelium. To test the direct effect of shear stress on endothelial cell adhesivity, endothelial cells were presheared for 2 to 6 hr at 2, 10, or 30 dynes/cm², and monocytic cell adherence was quantified at 1 dyne/cm². Adherence increased 330% or 370% when endothelial cells were presheared for 2 hr at 2 or 10 dynes/cm², respectively, as compared to unsheared endothelium. In contrast, when endothelial cells were presheared at 30 dynes/cm², monocytic cell adherence at 1 dyne/cm² was not significantly different from unsheared controls. Increased monocytic cell adherence to presheared endothelium was via a vasuclar cell adhesion molecule 1 (VCAM-1)α₄β₁ mechanism, and enzyme-linked immunosorbent assay studies showed that preshearing at 2 dynes/cm² for 2 hr increased endothelial VCAM-1 expression by 38%. These data demonstrated that low levels of shear stress induce enthelial VCAM-1 expression and increase monocytic cell adherence via a VCAM-1/α₄β₁ mechanism. Thus, shear stress can modulate monocyte adherence to vascular endothelium through drag forces that affect the establishment and maintenance of adhesive bonds and by directly modulating the expression of endothelial VCAM-1. This dual effect of shear stress produces the most favorable conditions for adhesion at low-shear regions, where drag forces are low and induction of VCAM-1 is likely. The preferential adherence of monocytes to these regions may contribute to the localization of atherosclerotic plaques to low-shear regions of the arterial circulationin vivo.     

Relationship between low intensity shear stress,aortic histamine formation,and aortic albumin uptake

The relationship between aortic histamine forming capacity (HFC) and aortic albumin uptake, as measured through fluorometric determination of the intraaortic content of bovine serum albumin conjugated to fluorescein isothiocyanate (FITCBSA) under steady-state conditions has been examined in relationship to the applied mean shear stress intensity created by pulsatile perfusion of rabbit aortas with platelet-free blood for a 1-hr period. HFC and FITCBSA determinations were made on aortic segments exposed to entrance and exit flow conditions as well as on those segments in which flow was stable; mean shear stresses in the latter ranged from 7 to 21 dynes/cm². Regression analyses between the HFC and intraaortic FITCBSA content yielded the equation y = 0.41x + 38.6, r = 0.81 (P < 0.005), where y = HFC and x = FITCBSA. These results indicate that the local rate of aortic histamine formation may influence local wall permeability to blood-borne macromolecules such as albumin; they also suggest that de novo histamine synthesis, mediated via the aortic histidine decarboxylase system, may have the potential of coupling altered hemodynamic states with subsequent alterations in wall resistance to macromolecule penetration and, as such, may have important ramifications with respect to vascular wall permeability increases involved in the initiation of atherosclerosis.     

Focal and regional patterns of uptake and the transmural distribution of 131-I-fibrinogen in the pig aorta in vivo

The focal and regional patterns of uptake, and the transmural distribution of human ¹³¹I-fibrinogen have been examined in the macroscopically normal pig aorta in vivo. Uptake of ¹³¹I-fibrinogen by focal areas of the aortic arch accumulating Evans blue dye (blue areas) was significantly greater than uptake into areas of the arch showing no dye accumulation (white areas) 2 hr after the intravenous injection of labeled fibrinogen. Not more than 5% of the ¹³¹I-fibrinogen was associated with the endothelium. Regional differences in the aortic uptake of ¹³¹I-fibrinogen were also observed; uptake into white areas of upper and lower abdominal aortic segments was significantly less than into white areas from the aortic arch.¹³¹I-Fibrinogen activity showed a distinct transmural gradient in each of the three regions of the aorta studied, namely, aortic arch and upper and lower abdominal aortic segments. As activity was greatest in the intima and inner media, the slope of the gradients has been interpreted as indicating fibrinogen entry from the endothelial surface. ¹³¹I-Fibrinogen activity was consistently greater in areas of dye accumulation than in white areas at each level across the aortic arch, although the greatest differences were observed in the intima and innermost media. Activity across the aortic wall in both the upper and lower abdominal segments was significantly less than in the arch at each of the levels studied. In the inner 300 μm the activity was less in the lower than in the upper abdominal segments.Fibrinogen influx rates were calculated for blue and white areas from the aortic arch, and for white areas in the upper and lower abdominal aortic segments. In the arch, calculated influx was 0.82±0.13 μg/cm²/hr in white areas, and 1.73 ± 0.30 μg/cm²/hr in blue areas. In both the upper and lower abdominal aortic segments, influx was approximately half that of white areas in the aortic arch. This study has shown that plasma ¹³¹I-fibrinogen crosses the normal aortic endothelium, and that the uptake shows both regional and focal differences. It is concluded that the presence of fibrinogen or fibrin in early atheromatous lesions may reflect the demonstrated permeability of normal aortic endothelium to circulating fibrinogen.     

Spatial variation of aortic wall oxygen diffusion coefficient from transient polarographic measurements

Polarographic current transients following a voltage step (turn-on transient) were measured with bare cathodes (25 μm diameter) and shallowly recessed oxygen microelectrodes (<5μm diameter). Except for the initial part of the current transient, the experimental measurements were in excellent agreement with simple models in the literature, which predict an inverse relationship with . Turn-on transients were measured in aqueous solutions with known physical properties, and in aortic wall tissue from three different species (n=6 rabbits, n=3 dogs, and n=1 miniature pig). Oxygen diffusion coefficients (D) were determinedin vitro by comparing time constants measured by the same microelectrode in saline and in strips of aortic wall tissue at 37°C. On the inner side (endothelium and intima) of the aorta, D averaged (±S.E.) 7.0 (±0.8)×10⁻⁶ cm²/s in 6 rabbits, 6.4 (±1.0)×10⁻⁶ cm²/s in 3 dogs, and was 4.6×10⁻⁶ cm²/s in the pig. On the adventitial side, D was 9.5×10⁻⁶ cm²/s in 1 rabbit, 11.4 (±1.2)×10⁻⁶ cm²/s in 3 dogs, and 8.1×10⁻⁶ cm²/s in the pig. For every aortic strip on which D was measured from both sides, D for the inner wall was always lower, overall by a little more than one third (p<0.001). The lower D on the endothelial side may limit oxygen transport to the vascular wall and play a role in atherogenesis.     

Influence of contraceptive and other sex steroids on aortic collagen and elastin

The effects of estradiol, progesterone, the contraceptive steroid combination mestranol-norethynodrel (M-N), and testosterone on aortic connective tissue were studied in ovariectomized and intact female rats. Estradiol and M-N administration to ovariectomized rats resulted in decreased accumulation of aortic collagen and elastin and, after injection of rats with [¹⁴C]proline, a lower specific activity of hydroxyproline in aortic collagen and elastin. The ratio of collagen to elastin ($\text{C}\text{E}$), which is an index of passive stiffness, was relatively low in aortas of all rats receiving female hormones and high in ovariectomized oil-treated and in testosterone-treated rats. Estradiol and M-N reduced $\text{C}\text{E}$ mainly by decreasing the percentage collagen, but progesterone reduced it by increasing the percentage elastin. It is concluded that sex hormones differentially alter aortic collagen and elastin synthesis and degradation and in so doing alter the accumulation and proportions of the two fibers in the vessel wall.     

Reduced cyclic stretch,endothelial dysfunction,and oxidative stress: an ex vivo model

BackgroundThe objective of this study was to investigate whether reduction of cyclic circumferential stretch will impair endothelial function and elevate basal levels of oxidative stress, both known risk factors linked to cardiovascular disease.MethodsEx vivo and in vitro models were used to perfuse porcine carotid arteries and porcine endothelial cells, respectively, for 24 h. In both cases, one group was allowed to stretch naturally when exposed to a pulse shear stress (6±3 dynes/cm²) combined with a pulse pressure of 80±10 mmHg, yielding a physiological cyclic stretch of 4–5%. This group was compared to a reduced stretch group, achieved by wrapping the arterial segment with a silicon band or by seeding the endothelial cells inside less compliant tubes, decreasing cyclic stretch to 1%.ResultsThe experimentally reduced compliance caused a significant decrease in bradykinin-dependent vascular relaxation. Reduced compliance significantly decreased the phosphorylation of serine 1177 (Ser1177) on eNOS, suggesting the activity of eNOS was decreased. Overall production of reactive oxygen species was increased by reducing compliance, as visualized with DHE. Finally, p22-phox and p47-phox, key players in the superoxide-generating NAD(P)H oxidase, were also up-regulated by reduced compliance.ConclusionsThese findings point out how reduced arterial compliance increases the risk of arterial disease by creating a less functional endothelium, interrupting the eNOS activation pathway, and increasing the vascular levels of oxidative stress.     

<Emphasis Type="Italic">In Vitro</Emphasis>, Time-Resolved PIV Comparison of the Effect of Stent Design on Wall Shear Stress

The effect of stent design on wall shear stress (WSS) and oscillatory shear index (OSI) was studied in vitro using time-resolved digital particle image velocimetry (DPIV). Four drug-eluting stents [XIENCE V^® (Abbott Vascular), TAXUS^® Liberté^® (Boston Scientific), Endeavor^® (Medtronic), and Cypher^® (J&;J Cordis)] and a bare-metal stent [VISION^® (Abbott Vascular)] were implanted into compliant vessel models, and the flow was measured in physiologically accurate coronary conditions featuring reversal and realistic offsets between pressure and flowrate. DPIV measurements were made at three locations under two different flow rates (resting: Re = 160, f = 70 bpm and exercise: Re = 300, f = 120 bpm). It was observed that design substantially affected the WSS experienced at the vessel walls. Averaged values between struts ranged from 2.05 dynes/cm² (Cypher^®) to 8.52 dynes/cm² (XIENCE V^®) in resting conditions, and from 3.72 dynes/cm² (Cypher^®) to 14.66 dynes/cm² (VISION^®) for the exercise state. Within the stent, the WSS dropped and the OSI increased immediately distal to each strut. In addition, an inverse correlation between average WSS and OSI existed. Comparisons with recently published results from animal studies show strong correlation between the measured WSS and observed endothelial cell coverage. These results suggest the importance of stent design on the WSS experienced by endothelial cells in coronary arteries.     

Antigen trapping cells in xenopus laevis: Tissue distribution

In the spleen of $\text{Xenopus laevis}$, antigen trapping (XL) cells are located at the periphery of the B-lymphocyte follicles and extend pseudopods through the boundary cell layer into the T-lymphocyte rich marginal zone to provide an anatomical bridge between the B-and T-cell compartments. The relationship between XL cells and nonsplenic antigen trapping cells was probed with a T-“independent” antigen, $\text{Aeromonas salmonicida}$. ¹²⁵I-$\text{Aeromonas}$ were trapped in high concentrations in marrow, spleen and liver. Splenic trapping was most efficient at low doses and liver trapping at high doses of antigen. Immunofluorescence stains demonstrated large cells with trapped $\text{Aeromonas}$ in spleen, marrow, liver, thymus, gut, kidney and blood. An antisera to XL cells stained large cells in all of these organs as well as vascular endothelium of the spleen, thymus, gut and lung. Thus, $\text{Xenopus}$ has a widely distributed system of antigen trapping cells that may be related to some vascular endothelial cells.     

Hemodynamic patterning of the avian atrioventricular valve

In this study, we develop an innovative approach to rigorously quantify the evolving hemodynamic environment of the atrioventricular (AV) canal of avian embryos. Ultrasound generated velocity profiles were imported into Micro‐Computed Tomography generated anatomically precise cardiac geometries between Hamburger‐Hamilton (HH) stages 17 and 30. Computational fluid dynamic simulations were then conducted and iterated until results mimicked in vivo observations. Blood flow in tubular hearts (HH17) was laminar with parallel streamlines, but strong vortices developed simultaneous with expansion of the cushions and septal walls. For all investigated stages, highest wall shear stresses (WSS) are localized to AV canal valve–forming regions. Peak WSS increased from 19.34 dynes/cm² at HH17 to 287.18 dynes/cm² at HH30, but spatiotemporally averaged WSS became 3.62 dynes/cm² for HH17 to 9.11 dynes/cm² for HH30. Hemodynamic changes often preceded and correlated with morphological changes. These results establish a quantitative baseline supporting future hemodynamic analyses and interpretations. Developmental Dynamics, 2011. © 2010 Wiley‐Liss, Inc.     

In vivo and in vitro comparison of fire ant venom and fire ant whole body extract

Thirty-four patients with a history of immediate hypersensitivity to the sting of the imported fire ant were evaluated in a study designed to compare the diagnostic usefulness of fire ant whole body extract (WBE) preparations with that of fire ant venom (IFAV). Ninety-one percent ($\text{31}\text{34}$) of the hypersensitive patients skin tested with IFAV at a maximal concentration of 1:5 × 10³, $\text{v}\text{v}$, demonstrated a wheat equal to or greater than the histamine control. Fifty-three percent ($\text{18}\text{34}$) of the group were skin test positive to a WBE preparation. When the criteria for a positive skin test were relaxed, 82% of the hypersensitive group could be identified with the IFAWBE. A comparison of skin test results in sensitive patients revealed variability in the sensitivity of the WBE preparations utilized in the study. Leukocyte histamine release demonstrated a dose-response release of histamine with both IFAV and SIWBEa preparations. Specific venom antisera produced in rabbits identified a precipitin line of common identity in a gel-diffusion system containing IFAWBE and IFAV. This finding was verified by the competitive inhibition of IFAWBE with IFAV in a solid-phase radioimmunoassay system. Fire ant WBEs contain venom constituents and are effective diagnostic agents in up to 82% of patients with hypersensitivity to the sting of the imported fire ant. Marked variability in the responsiveness of sensitive patients to different WBE preparations mandates standardization of these diagnostic preparations.     

The relationship of plasma histamine to the activity of bronchial asthma

Venous plasma histamine levels were measured in 60 asthmatic subjects in order to investigate the role of histamine in naturally occurring asthmatic episodes. The patients were divided into 3 groups of 20 according to the degree of disease activity. Group A consisted of asthmatic patients with severe exacerbations. Flow/volume curves demonstrated a forced expiratory volume in 1 sec to forced vital capacity ratio ($\text{FEV}{}_1\text{FVC}$) of less than 55% and a maximum expiratory flow at 50% of FVC (MEF₅₀) of less than 1.0 L/sec. Asthmatics in group B were in partial remission. The patients in this group had $\text{FEV}{}_1\text{FVC}$ ratios between 55% and 75% and MEF₅₀ values between 1.0 and 4.0 L/sec. The remaining asthmatic patients (group C) were in complete remission. They were asymptomatic and had normal physical examinations and flow/volume curves. Venous plasma histamine levels were also measured in 50 normal control subjects (group D). Every asthmatic subject in group A had plasma histamine above 1.25 ng/ml (mean, 1.9 ng/ml ± 0.5). Only 3 asthmatic patients in group B and 3 in group C had venous plasma histamine levels greater than 1 ng/ml. None of the normal subjects in group D had plasma histamine above 1 ng/ml. These data show a relationship between spontaneously occurring asthmatic attacks and elevated plasma histamine and support previous studies suggesting that histamine may play a role in the mediation of bronchial asthma.     

An E-selectin-IgG chimera supports sialylated moiety dependent adhesion of colon carcinoma cells under fluid flow

To further characterize the molecular mechanisms that govern carcinoma cell adhesion to stimulated endothelium, we studied the adhesion of a human colon carcinoma cell line, KM12-L4, to an E-selectin-IgG₁ chimera and interleukin (IL)-1β-stimulated human umbilical vein endothelial cells (HUVEC) underin vitro fluid flow conditions. Between 0.6 and 1.8 dynes/cm², KM12-L4 cells attach to and roll on IL-1β-stimulated HUVEC. The adhesion is E-selectin dependent and diminished upon pretreatment of the KM12-L4 cells with neuraminidase (neuraminidase sensitive). Between 0.7 and 1.8 dynes/cm², surfaces coated with an E-selectin-IgG₁ chimera support attachment and rolling of KM12-L4 cells. The adhesion to the E-selectin-IgG₁ chimera is blocked by an antibody to the lectin domain of E-selectin and is neuraminidase sensitive. Rolling KM12-L4 cells exhibit variable velocity motion over both IL-1β-stimulated HUVEC and E-selectin-IgG₁ chimera-coated surfaces. Our results provide the first direct evidence that sialylated moieties are involved in the adhesion of carcinoma cells to IL-1β-stimulated endothelium under flow conditions; E-selectin-IgG₁ chimeras can support cell attachment and rolling under defined flow conditions; the topology of the endothelium is not the sole cause of variable velocity motion observed in cell rolling systems.     

Human versus bovine endothelial cell culture on glass and tissue-culture plastic

Summary This work demonstrates that human umbilical vein endothelial cells (HUVECs; Passages 1 and 5) attach to and grow on glass poorly in comparison to bovine aortic endothelial cells (BAECs; Passage 5). Seventeen hours after seeding passage 5 cells, there are 6.0±0.1 × 10³ HUVECs/cm² (mean±SE,n=12) on gelatin-coated glass, vs. 29.3±1.5 × 10³ BAECs/cm². This poor attachment and growth is due to a dependence of HUVECs on surface charge and preadsorbed fibronectin not shared by BAECs, because both cell types proliferate on tissue culture plastic and HUVECs can be made to grow comparably well on gelatin-coated glass by the further addition of poly-l-lysine and fibronectin. These data indicate the existence of a human-bovine species difference with respect to endothelial cell adhesion to and growth on glass. This work was supported by a grant from the National Institutes of Health (HL 33095), Bethesda, MD.     

Evidence of nucleosomes in situ and their organization in chromatin and chromosomes of Chinese hamster cells

Freeze-fracture studies of intact metaphase Chinese hamster cells indicate that the chromosomes are composed of compactly aligned, flat and hexagonally shaped bipartite disks. The overall dimensions of a bipartite disk are about $\text{140 ± 25}\text{A}\text{?}$ in height, $\text{100 ± 20}\text{A}\text{?}$ in width, and $\text{54 ± 4}\text{A}\text{?}$ in thickness. The center-to-center distance of two units of a bipartite disk is about $\text{34 ± 3}\text{A}\text{?}$. The core of a disk appears to contain four substructures that measure about $\text{25 ± 5}\text{A}\text{?}$ in diameter. Through the center of the disk core there is an axial structure measuring about $\text{20 ± 5}\text{A}\text{?}$ in diameter, which spans and interconnects similar bipartite disks to form a continuous linear array. A structure measuring $\text{20 ± 4}\text{A}\text{?}$ in diameter is wound around the edges of the disk core and interconnects with the next bipartite disk. The connecting strand is parallel to the axial structure. In addition, there appear to be bridgings between the curled structure and disk core. The chromatin of intact interphase cell nuclei shows similar bipartite disks with dimensions and features similar to those of metaphase chromosomes. The bipartite disks are aligned in a linear array in both chromatin and chromosomes.     

Quantification of head sweating during rest and exercise in the heat

The head’s capacity for evaporative heat loss is important for design of protective helmets for use in hot environments. This study quantified head sweating rate (m _sw) in eight males during rest and exercise at three metabolic rates (338 ± 36, 481 ± 24, 622 ± 28 W) in hot-dry (HD: 45 °C, 21 % RH) and hot-wet (HW: 35 °C, 69 % RH) conditions (matched at 31.6 °C WBGT), which were counterbalanced. Heads were shaved, and surface area was (458 ± 61 cm²) measured by 3D scanner. For measurement of head m _sw, dry air was passed through a sealed helmet, whereas for forearm m _sw a capsule (15.9 cm²) was ventilated with ambient air. Evaporation rate was determined from the increase in vapor pressure in the exiting air. Whole-body sweat loss was calculated from the change in nude weight plus fluid intake and corrected for respiratory fluid losses. Head m _sw increased (p = 0.001) with metabolic rate, and was lower (p = 0.018) in HD (0.4 ± 0.2 mg cm^?2 min^?1 at rest to 1.1 ± 0.6 mg cm^?2 min^?1 at 622 W), compared to HW (0.5 ± 0.3–1.4 ± 0.8 mg cm^?2 min^?1). Forearm m _sw increased (p < 0.001) with metabolic rate, but was higher (p = 0.002) in HD (0.4 ± 0.3–1.4 ± 0.7 mg cm^?2 min^?1) than HW (0.1 ± 0.1–1.1 ± 0.3 mg cm^?2 min^?1). Whole-body sweat loss was not significantly different (p = 0.06) between HD (647 ± 139 g m^?2 h^?1) and HW (528 ± 189 g m^?2 h^?1). This study demonstrates the importance of the head for evaporative heat loss, particularly for populations who wear protective clothing which can impair vapor transfer from the skin.     

Dopamine-β-hydroxylase activity in normal and sympathectomized carotid bodies

Normal carotid bodies excised from cats showed DBH values of 5.04 ± 0.53 nmol [³H]octopamine formed/h/100 mg tissue ($\text{x}\text{?}\text{±}\text{S.E.}$). Values from sympathectomized carotid bodies were not significantly different. While the ganglio-glomerular nerves, providing the sympathetic innervation of the carotid bifurcation, had a high DBH level, this was low in the carotid sinus nerve, providing its sensory innervation. Glomeral DBH may be contained in a special type of noradrenergic glomus cells, distinct from the most common dopaminergic glomus cells.     

An E-selectin-IgG chimera supports sialylated moiety dependent adhesion of colon carcinoma cells under fluid flow

To further characterize the molecular mechanisms that govern carcinoma cell adhesion to stimulated endothelium, we studied the adhesion of a human colon carcinoma cell line, KM12-L4, to an E-selectin-IgG₁ chimera and interleukin (IL)-1β-stimulated human umbilical vein endothelial cells (HUVEC) underin vitro fluid flow conditions. Between 0.6 and 1.8 dynes/cm², KM12-L4 cells attach to and roll on IL-1β-stimulated HUVEC. The adhesion is E-selectin dependent and diminished upon pretreatment of the KM12-L4 cells with neuraminidase (neuraminidase sensitive). Between 0.7 and 1.8 dynes/cm², surfaces coated with an E-selectin-IgG₁ chimera support attachment and rolling of KM12-L4 cells. The adhesion to the E-selectin-IgG₁ chimera is blocked by an antibody to the lectin domain of E-selectin and is neuraminidase sensitive. Rolling KM12-L4 cells exhibit variable velocity motion over both IL-1β-stimulated HUVEC and E-selectin-IgG₁ chimera-coated surfaces. Our results provide the first direct evidence that sialylated moieties are involved in the adhesion of carcinoma cells to IL-1β-stimulated endothelium under flow conditions; E-selectin-IgG₁ chimeras can support cell attachment and rolling under defined flow conditions; the topology of the endothelium is not the sole cause of variable velocity motion observed in cell rolling systems.     

Autophagy Regulates Vascular Endothelial Cell eNOS and ET-1 Expression Induced by Laminar Shear Stress in an Ex Vivo Perfused System

Vascular endothelial cell function responds to steady laminar shear stress; however, the underlying mechanisms are not fully elucidated. In the present study, we examined the effect of steady laminar shear stress on vascular endothelial cell autophagy and endothelial cell nitric oxide synthase (eNOS) and endothelin-1 (ET-1) expression using an ex vivo perfusion system. Human vascular endothelial cells and common arteries of New Zealand rabbits were pretreated with or without rapamycin or 3-MA for 30 min. These were then placed in an ex vivo cell perfusion system or an ex vivo organ perfusion system under static conditions (0 dynes/cm²) or steady laminar shear stress (5 or 15 dynes/cm²) for 1 h. In both ex vivo perfusion vascular endothelial cells and vascular vessel segment, steady laminar shear stress promoted autophagy and eNOS expression and inhibited ET-1 expression. Compared with steady laminar shear stress treatment alone, the pretreatment of autophagy inducer rapamycin obviously strengthened the expression of eNOS and decreased the expression of ET-1 in both the 5 and 15 dynes/cm² treatment groups. Moreover, when pretreated with the autophagy inhibitor 3-MA, the eNOS expression was obviously inhibited and the ET-1 expression was reversed. These findings demonstrate that autophagy is upregulated under steady laminar shear stress, improving endothelial cell maintenance of vascular tone function.     

Hemodynamic Regulation of Inflammation at the Endothelial–Neutrophil Interface

Arterial shear stress can regulate endothelial phenotype. The potential for anti-inflammatory effects of shear stress on TNFα-activated endothelium was tested in assays of cytokine expression and neutrophil adhesion. In cultured human aortic endothelial cells (HAEC), arterial shear stress of 10 dyne/cm² blocked by >80% the induction by 5 ng/mL TNFα of interleukin-8 (IL-8) and IL-6 secretion (50 and 90% reduction, respectively, in the presence of nitric oxide synthase antagonism with 200 μM nitro-l-arginine methylester, l-NAME). Exposure of TNFα-stimulated HAEC to arterial shear stress for 5 h also reduced by 60% (p < 0.001) the conversion of neutrophil rolling to firm arrest in a venous flow assay conducted at 1 dyne/cm². Also, neutrophil rolling lengths at 1 dyne/cm² were longer when TNFα-stimulated HAEC were presheared for 5 h at arterial stresses. In experiments with a synthetic promoter that provides luciferase induction to detect cis interactions of glucocorticoid receptor (GR) and NFκB, shear stress caused a marked 40-fold induction of luciferase in TNFα-treated cells, suggesting a role for GR pathways in the anti-inflammatory actions of fluid shear stress. Hemodynamic force exerts anti-inflammatory effects on cytokine-activated endothelium by attenuation of cytokine expression and neutrophil firm arrest.