剪切应力对毛细血管内皮细胞代谢的影响

建立的平行平板流协腔装置适用于研究血管内皮细胞代谢对剪切流场的响应。将培养的人胚肾小球血管单层内皮细胞置于剪应力分别为５＊１０＾－５Ｎ／ｃｍ＾２,１＊１０＾－４Ｎ／ｃｍ＾２和１．５＊１０＾－４Ｎ／ｃｍ＾２的定常层流中剪切２５小时。     

Local hemodynamics affect monocytic cell adhesion to a three-dimensional flow model coated with E-selectin.

Monocyte adhesion to the endothelium depends on concentrations of receptors/ligands, local concentrations of chemoattractants, monocyte transport to the endothelial surface and hemodynamic forces. Monocyte adhesion to the inert surface of a three-dimensional perfusion model was shown to correlate inversely with wall shear stress, but was also affected by flow patterns which influenced the near-wall cell availability. We hypothesized that (a) under the same flow conditions, insolubilized E-selectin on the model's surface may mediate adhesive interactions at higher wall shear stresses, compared to an uncoated model, and (b) pulsatile flow may modify the adhesion profile obtained under steady flow. An axisymmetric flow model with a stenosis and a sudden expansion produced a range of wall shear stresses and a separated flow with recirculation and reattachment. Pre-activated U937 cells were perfused through the model under either steady (Re = 100, 140) or pulsatile (Remean = 107) flow. The velocity field was characterized through computational fluid dynamics and validated by inert particle tracking. Surface E-selectin greatly increased cell adhesion in all regions at Re = 100 and 140, compared to an uncoated model under the same flow conditions. In regions where the cells near the wall were abundant (taper and stenosis), adhesion to E-selectin correlated with the reciprocal of local wall shear stress when flow was steady. Pulsatile flow distributed the adherent cells more evenly throughout the coated model. Hence, characterizing both the local hemodynamics and the biological activity on the vessel wall is important in leukocyte adhesion.     

Flow in the well: computational fluid dynamics is essential in flow chamber construction

A perfusion system was developed to generate well defined flow conditions within a well of a standard multidish. Human vein endothelial cells were cultured under flow conditions and cell response was analyzed by microscopy. Endothelial cells became elongated and spindle shaped. As demonstrated by computational fluid dynamics (CFD), cells were cultured under well defined but time varying shear stress conditions. A damper system was introduced which reduced pulsatile flow when using volumetric pumps. The flow and the wall shear stress distribution were analyzed by CFD for the steady and unsteady flow field. Usage of the volumetric pump caused variations of the wall shear stresses despite the controlled fluid environment and introduction of a damper system. Therefore the use of CFD analysis and experimental validation is critical in developing flow chambers and studying cell response to shear stress. The system presented gives an effortless flow chamber setup within a 6-well standard multidish.     

Effect of shear stress on expression of a recombinant protein by Chinese hamster ovary cells

A flow chamber was used to impart a steady laminar shear stress on a recombinant Chinese hamster ovary (CHO) cell line expressing human growth hormone (hGH). The cells were subjected to shear stress ranging from 0.005 to 0.80 N m(-2). The effect of shear stress on the cell specific glucose uptake, cell specific hGH, and lactate productivity rates were calculated. No morphological changes to the cells were observed over the range of shear stresses examined. When the cells were subjected to 0.10 N m(-2) shear in protein-free media without Pluronic F-68, recombinant protein production ceased with no change in cell morphology, whereas control cultures were expressing hGH at 0.35 microg/10(6 )cells/h. Upon addition of the shear protectants, Pluronic F-68 (0.2% [w/v]) or fetal bovine serum (1.0% [v/v] FBS), the productivity of the cells was restored. The effect of increasing shear stress on the cells in protein-free medium containing Pluronic F-68 was also investigated. Cell specific metabolic rates were calculated for cells under shear stress and for no-shear control cultures performed in parallel, with shear stress rates expressed as a percentage of those obtained for control cultures. Upon increasing shear from 0.005 to 0.80 N m(-2), the cell specific hGH productivity decreased from 100% at 0.005 N m(-2) to 49% at 0.80 N m(-2) relative to the no-shear control. A concurrent increase in the glucose uptake rate from 115% at 0.01 N m(-2) to 142% at 0.80 N m(-2), and decreased lactate productivity from 92% to 50%, revealed a change in the yield of products from glucose compared with the static control. It was shown that shear stress, at sublytic levels in medium containing Pluronic F-68, could decrease hGH specific productivity.     

Effects of pulsatile flow on cultured vascular endothelial cell morphology

Endothelial cells (EC) appear to adapt their morphology and function to the in vivo hemodynamic environment in which they reside. In vitro experiments indicate that similar alterations occur for cultured EC exposed to a laminar steady-state flow-induced shear stress. However, in vivo EC are exposed to a pulsatile flow environment; thus, in this investigation, the influence of pulsatile flow on cell shape and orientation and on actin microfilament localization in confluent bovine aortic endothelial cell (BAEC) monolayers was studied using a 1-Hz nonreversing sinusoidal shear stress of 40 +/- 20 dynes/cm2 (type I), 1-Hz reversing sinusoidal shear stresses of 20 +/- 40 and 10 +/- 15 dynes/cm2 (type II), and 1-Hz oscillatory shear stresses of 0 +/- 20 and 0 +/- 40 dynes/cm2 (type III). The results show that in a type I nonreversing flow, cell shape changed less rapidly, but cells took on a more elongated shape than their steady flow controls long-term. For low-amplitude type II reversing flow, BAECs changed less rapidly in shape and were always less elongated than their steady controls; however, for high amplitude reversal, BAECs did not stay attached for more than 24 hours. For type III oscillatory flows, BAEC cell shape remained polygonal as in static culture and did not exhibit actin stress fibers, such as occurred in all other flows. These results demonstrate that EC can discriminate between different types of pulsatile flow environments.(ABSTRACT TRUNCATED AT 250 WORDS)     

An apparatus to study the response of cultured endothelium to shear stress

An apparatus which has been developed to study the response of cultured endothelial cells to a wide range of shear stress levels is described. Controlled laminar flow through a rectangular tube was used to generate fluid shear stress over a cell-lined coverslip comprising part of one wall of the tube. A finite element method was used to calculate shear stresses corresponding to cell position on the coverslip. Validity of the finite element analysis was demonstrated first by its ability to generate correctly velocity profiles and wall shear stresses for laminar flow in the entrance region between infinitely wide parallel plates (two-dimensional flow). The computer analysis also correctly predicted values for pressure difference between two points in the test region of the apparatus for the range of flow rates used in these experiments. These predictions thus supported the use of such an analysis for three-dimensional flow. This apparatus has been used in a series of experiments to confirm its utility for testing applications. In these studies, endothelial cells were exposed to shear stresses of 60 and 128 dynes/cm2. After 12 hr at 60 dynes/cm2, cells became aligned with their longitudinal axes parallel to the direction of flow. In contrast, cells exposed to 128 dynes/cm2 required 36 hr to achieve a similar reorientation. Interestingly, after 6 hr at 128 dynes/cm2, specimens passed through an intermediate phase in which cells were aligned perpendicular to flow direction. Because of its ease and use and the provided documentation of wall shear stress, this flow chamber should prove to be a valuable tool in endothelial research related to atherosclerosis.     

Induction of mammalian cell death by simple shear and extensional flows

In this work we investigated whether the type of shear flow, to which cells are exposed, influences the initiation of cell death. It is shown that mammalian cells, indeed, distinguish between discrete types of flow and respond differently. Two flow devices were employed to impose accurate hydrodynamic flow fields: uniform steady simple shear flow and oscillating extensional flow. To distinguish between necrotic and apoptotic cell death, fluorescence activated cell sorting and the release of DNA in the culture supernatant was used. Results show that Chinese Hamster Ovaries and Human Embryonic Kidney cells will enter the apoptotic pathway when subjected to low levels of hydrodynamic stress (around 2.0 Pa) in oscillating, extensional flow. In contrast, necrotic death prevails when the cells are exposed to hydrodynamic stresses around 1.0 Pa in simple shear flow or around 500 Pa in extensional flow. These threshold values at which cells enter the respective death pathway should be avoided when culturing cells for recombinant protein production to enhance culture longevity and productivity. Biotechnol. Bioeng. 2009; 104: 360–370 © 2009 Wiley Periodicals, Inc.     

Flow-induced wall shear stress in abdominal aortic aneurysms: Part II--pulsatile flow hemodynamics

In continuing the investigation of AAA hemodynamics, unsteady flow-induced stresses are presented for pulsatile blood flow through the double-aneurysm model described in Part I. Physiologically realistic aortic blood flow is simulated under pulsatile conditions for the range of time-average Reynolds numbers 50< or =Re(m) < or =300. Hemodynamic disturbance is evaluated for a modified set of indicator functions which include wall pressure (p(w)), wall shear stress (tau(w)), Wall Shear Stress Gradient (WSSG), time-average wall shear stress (tau(w)*), and time-average Wall Shear Stress Gradient WSSG*. At peak flow, the highest shear stress and WSSG levels are obtained at the distal end of both aneurysms, in a pattern similar to that of steady flow. The maximum values of wall shear stresses and wall shear stress gradients are evaluated as a function of the time-average Reynolds number resulting in a fourth order polynomial correlation. A comparison between numerical predictions for steady and pulsatile flow is presented, illustrating the importance of considering time-dependent flow for the evaluation of hemodynamic indicators.     

Flow-induced Wall Shear Stress in Abdominal Aortic Aneurysms: Part II - Pulsatile Flow Hemodynamics

In continuing the investigation of AAA hemodynamics, unsteady flow-induced stresses are presented for pulsatile blood flow through the double-aneurysm model described in Part I. Physiologically realistic aortic blood flow is simulated under pulsatile conditions for the range of time-average Reynolds numbers 50 h Re m h 300. Hemodynamic disturbance is evaluated for a modified set of indicator functions which include wall pressure ( p w ), wall shear stress ( w ), Wall Shear Stress Gradient (WSSG), time-average wall shear stress ( w *), and time-average Wall Shear Stress Gradient WSSG *. At peak flow, the highest shear stress and WSSG levels are obtained at the distal end of both aneurysms, in a pattern similar to that of steady flow. The maximum values of wall shear stresses and wall shear stress gradients are evaluated as a function of the time-average Reynolds number resulting in a fourth order polynomial correlation. A comparison between numerical predictions for steady and pulsatile flow is presented, illustrating the importance of considering time-dependent flow for the evaluation of hemodynamic indicators.     

Cell morphological response to low shear stress in a two-dimensional culture microsystem with magnitudes comparable to interstitial shear stress

Slow interstitial flow can lead to large changes in cell morphology. Since conventional biological assays are adapted to two-dimensional culture protocols, there is a need to develop a microfluidic system that can generate physiological levels of interstitial flow. Here we developed a system that uses a passive osmotic pumping mechanism to generate sustained and steady interstitial flows for two-dimensional cultures. Two different cell types, fibroblasts and mesenchymal stem cells, were selected because they are generally exposed to interstitial flow. To quantify the cellular response to interstitial shear flow in terms of proliferation and alignment, 4 rates of flow were applied. We found that the proliferation rate of fibroblasts varied linearly with wall shear stress. In addition, alignment of fibroblast cells depended linearly on the magnitude of the shear stress, whereas mesenchymal stem cells were aligned regardless of the magnitude of shear stress. This suggested that mesenchymal stem cells are very sensitive to shear stresses, even at levels generated by interstitial flow. The results presented here emphasize the need to consider the mechanosensitivity and the natural role of different cell types when evaluating their responses to fluid flow.     

Establishment of a microcarrier culture system with serial sub-cultivation for functionally active human endothelial cells

A microcarrier culture system was established for a large-scale production of functional human endothelial cells. It has been difficult to cultivate human endothelial cells in large quantities for the reasons that specific growth factor and extracellular matrix are required for the survival and proliferation of the cells and the life span of the primary cells are limited. A lot of studies have reported that the shear stress gives significant influences on the structure, growth rate and biological functions of endothelial cells. We aimed to develop a convenient microcarrier culture system for human endothelial cells which can reproduce the flow effects experienced in vivo or in vitro. In 200 mL volume culture, human umbilical vein endothelial cells (HUVEC) could be serially sub-cultivated by optimizing the culture conditions such as shear strength, growth factor, beads and seeding cell concentration, serum concentration, and passage timing. The growth rate was enhanced depending on the shear strength and the life span of the cells was elongated until over 43PDL which is much longer than those of monolayer cultures. The cells maintained the diploidy of over 80% without obvious abnormal changes in the chromosomes. The serially sub-cultured microcarrier cells maintained various endothelial cell functions such as the syntheses of von Willebrand factor (vWf), prostacyclin and other biological substances, the expression of CD31, and the VEGF(165) dependent growth characteristic. The synthesis of biological products was affected by shear strength. In the case of prostacyclin, a different synthesis response was observed between steady flow and transiently reduced shear strength. The synthesis of endothelin-1 (ET-1) was down-regulated by increase of shear strength different from those of other products. The culture system was scaled up until 2 L volume under the optimum DO control. The cells synthesized IL-6 in response to shear strength. These results indicate that the established microcarrier system might be able to contribute to the supply of functional human endothelial cells for various medical applications such as the reconstruction of injured blood vessels caused by atherosclerosis or restenosis of coronary arteries after angioplasty, and the construction of an anti-coagulable artificial blood vessel or an artificial skin with good transplant-ability.     

Cross talk of shear-induced production of prostacyclin and nitric oxide in endothelial cells

We tested the hypothesis that vessel homeostasis is maintained through the cross talk of shear-induced production of prostacyclin and nitric oxide (NO). Confluent human umbilical vein endothelial cells (HUVEC) were exposed to fluid shear stress at 15 dyn/cm(2) using a cone-plate device, and the concentrations of 6-keto-PGF(1alpha) and NO metabolites (nitrate and nitrite) in the medium were measured with radioimmunoassay and the Greiss method, respectively. Compared with static control, shear stress increased cumulative prostacyclin production by twofold after 90 min of exposure. Inhibition of NO synthase enhanced flow-induced prostacyclin production by twofold without affecting the baseline production. Guanylyl cyclase inhibitor enhanced flow-induced prostacyclin production to the same degree. In contrast, a stable agonist of cGMP attenuated the rapid early phase of flow-dependent prostacyclin production. Shear-induced NO metabolite production was unaffected even after indomethacin inhibited prostacyclin production. We conclude that NO shows an inhibitory effect on prostacyclin production under shear stress and that vessel homeostasis may be maintained through an increase in prostacyclin production when NO synthesis is impaired in endothelial cells.     

Computational simulations predict a key role for oscillatory fluid shear stress in de novo valvular tissue formation

Previous efforts in heart valve tissue engineering demonstrated that the combined effect of cyclic flexure and steady flow on bone marrow derived stem cell-seeded scaffolds resulted in significant increases in engineered collagen formation [Engelmayr et al. Cyclic flexure and laminar flow synergistically accelerate mesenchymal stem cell-mediated engineered tissue formation: Implications for engineered heart valve tissues. Biomaterials 2006; 27(36): 6083–95]. Here, we provide a new interpretation for the underlying reason for this observed effect. In addition, another related investigation demonstrated the impact of fluid flow on DNA content and quantified the fluid-induced shear stresses on the engineered heart valve tissue specimens [Engelmayr et al. A Novel Flex-Stretch-Flow Bioreactor for the Study of Engineered Heart Valve Tissue Mechanobiology]. Annals of Biomedical Engineering 2008, 36, 1–13]. In this study, we performed more advanced CFD analysis with an emphasis on oscillatory wall shear stresses imparted on specimens when mechanically conditioned by a combination of cyclic flexure and steady flow. Specifically, we hypothesized that the dominant stimulatory regulator of the bone marrow stem cells is fluid-induced and depends on both the magnitude and temporal directionality of surface stresses, i.e., oscillatory shear stresses (OSS) acting on the developing tissues. Therefore, we computationally quantified the (i) magnitude of fluid-induced shear stresses as well as (ii) the extent of temporal fluid oscillations in the flow field using the oscillatory shear index (OSI) parameter. Noting that sample cyclic flexure induces a high degree of OSS, we incorporated moving boundary computational fluid dynamic simulations of samples housed within a bioreactor to consider the effects of: (1) No Flow, No Flexure (control group), (2) Steady Flow-alone, (3) Cyclic Flexure-alone and (4) Combined Steady flow and Cyclic Flexure environments. Indeed we found that the coexistence of both OSS and appreciable shear stress magnitudes explained the high levels of engineered collagen previously observed from combining cyclic flexure and steady flow states. On the other hand, each of these metrics on its own showed no association. This finding suggests that cyclic flexure and steady flow synergistically promote engineered heart valve tissue production via OSS, so long as the oscillations are accompanied by a critical magnitude of shear stress.     

Osteoblasts respond to pulsatile fluid flow with short-term increases in PGE(2) but no change in mineralization.

Although there is no consensus as to the precise nature of the mechanostimulatory signals imparted to the bone cells during remodeling, it has been postulated that deformation-induced fluid flow plays a role in the mechanotransduction pathway. In vitro, osteoblasts respond to fluid shear stress with an increase in PGE(2) production; however, the long-term effects of fluid shear stress on cell proliferation and differentiation have not been examined. The goal of this study was to apply continuous pulsatile fluid shear stresses to osteoblasts and determine whether the initial production of PGE(2) is associated with long-term biochemical changes. The acute response of bone cells to a pulsatile fluid shear stress (0.6 +/- 0.5 Pa, 3.0 Hz) was characterized by a transient fourfold increase in PGE(2) production. After 7 days of static culture (0 dyn/cm(2)) or low (0.06 +/- 0.05 Pa, 0.3 Hz) or high (0.6 +/- 0.5 Pa, 3.0 Hz) levels of pulsatile fluid shear stress, the bone cells responded with an 83% average increase in cell number, but no statistical difference (P > 0.53) between the groups was observed. Alkaline phosphatase activity per cell decreased in the static cultures but not in the low- or high-flow groups. Mineralization was also unaffected by the different levels of applied shear stress. Our results indicate that short-term changes in PGE(2) levels caused by pulsatile fluid flow are not associated with long-term changes in proliferation or mineralization of bone cells.     

Shear stress enhances prostacyclin release from endocardial endothelial cells

The effect of shear stress on the release of prostacyclin (PGI2) from cultured endocardial endothelial cells (EECs) was investigated. EECs were harvested from the right ventricle (RV) and the left ventricle (LV) of porcine heart. Confluent EECs were incubated under various degrees of shear stress (0.2, 1, 4 and 6 dyne/cm2) and PGI2 release from each cell was measured. PGI2 release from LV-EECs and RV-EECs was enhanced by the elevation of shear stress in a shear-dependent manner with a rapid increase at the onset of flow; however, there was no significant difference in PGI2 production between RV-EECs and LV-EECs. production of PGI2 was significantly inhibited from cells exposed to 8-(dimetilamino) octyl 3,4,5-trymethoxybenzoate hydrochloride (10 and 100 microM: an inhibitor of intracellular calcium mobilization) or cyclopiazonic acid (10 microM: an endoplasmic reticulum Ca2+-ATPase inhibitor). These results indicate that shear stress enhances PGI2 release from cultured EECs and that mechanotransduction of shear stress depends on calcium mobilization in EECs.     

Cells in fluidic environments are sensitive to flow frequency

Virtually all cells accommodate to their mechanical environment. In particular, cells subject to flow respond to rapid changes in fluid shear stress (SS), cyclic stretch (CS), and pressure. Recent studies have focused on the effect of pulsatility on cellular behavior. Since cells of many different tissue beds are constantly exposed to fluid flows over a narrow range of frequencies, we hypothesized that an intrinsic flow frequency that is optimal for determining cell phenotype exists. We report here that cells from various tissue beds (bovine aortic endothelial cells (BAEC), rat small intestine epithelial cells (RSIEC), and rat lung epithelial cells (RLEC)) proliferate maximally when cultured in a perfusion bioreactor under pulsatile conditions at a specific frequency, independent of the applied SS. Vascular endothelial and pulmonary epithelial cell proliferation peaked under 1 Hz pulsatile flow. In contrast, proliferation of gastrointestinal cells, which in their physiological context are subject to no flow or higher wavelength signal, was maximum at 0.125 Hz or under no flow. Moreover, exposure of BAEC to pulsatile flow of varying frequency influenced their nitric oxide synthase activity and prostacyclin production, which reached maximum values at 1 Hz. Notably, the "optimal" frequencies for the cell types examined correspond to the physiologic operating range of the organs from where they were initially derived. These findings suggest that frequency, independent of shear, is an essential determinant of cell response in pulsatile environments.     

Blood flow in abdominal aortic aneurysms: pulsatile flow hemodynamics

Numerical predictions of blood flow patterns and hemodynamic stresses in Abdominal Aortic Aneurysms (AAAs) are performed in a two-aneurysm, axisymmetric, rigid wall model using the spectral element method. Physiologically realistic aortic blood flow is simulated under pulsatile conditions for the range of time-averaged Reynolds numbers 50< or =Re(m)< or =300, corresponding to a range of peak Reynolds numbers 262.5< or =Re(peak) < or = 1575. The vortex dynamics induced by pulsatile flow in AAAs is characterized by a sequence of five different flow phases in one period of the flow cycle. Hemodynamic disturbance is evaluated for a modified set of indicator functions, which include wall pressure (p(w)), wall shear stress (tau(w)), and Wall Shear Stress Gradient (WSSG). At peak flow, the highest shear stress and WSSG levels are obtained downstream of both aneurysms, in a pattern similar to that of steady flow. Maximum values of wall shear stresses and wall shear stress gradients obtained at peak flow are evaluated as a function of the time-average Reynolds number resulting in a fourth order polynomial correlation. A comparison between predictions for steady and pulsatile flow is presented, illustrating the importance of considering time-dependent flow for the evaluation of hemodynamic indicators.     

Red blood cell deformation in shear flow. Effects of internal and external phase viscosity and of in vivo aging.

Shear deformation of young and old human red blood cells was examined over a range of shear stresses and suspending phase viscosities (eta o) using a cone-plate Rheoscope. The internal viscosities (eta i) of these cell types differ, and further changes in internal viscosity were induced by alteration of suspension osmolality and hence cell volume. For low suspending viscosities (0.0555 or 0.111 P) old cells tended to tumble in shear flow, whereas young cells achieved stable orientation and deformed. Changes in osmolality, at these external viscosities, altered the percentage of cells deforming, and for each cell type threshold osmolalities (Osm-50) were determined where 50% of cells deformed. The threshold osmolalities were higher for younger cells than for older cells, but the internal viscosities of the two cell types were similar at their respective Osm-50. Threshold osmolalities were also higher for the higher external viscosity, but the ratio of internal to external viscosities (i.e., eta i/eta o) was nearly constant for both external viscosities. Deformation of stably oriented cells increased with increasing shear stress and approached a value limited by cell surface area and volume. For isotonic media, over a wide range of external viscosities and shear stresses, deformation was greater for younger cells than for older cells. However, deformation vs. shear stress data for the two cell types became nearly coincident if young cells were osmotically shrunk to have their internal viscosity close to that for old cells. Increases in external viscosity, at constant shear stress, caused greater deformation for all cells. This effect of external viscosity was not equal for young and old cells; the ratio of old/young cell deformation increased with increasing eta o. However, if deformation was plotted as a function of the ratio lambda = eta i/eta o, at constant shear stress, young and old cell data followed similar paths. Thus the ratio lambda is a major determinant of cell deformation as well as a critical factor affecting stable orientation in shear flow.     

The elongation and orientation of cultured endothelial cells in response to shear stress

Vascular endothelial cells appear to be aligned with the flow in the immediate vicinity of the arterial wall and have a shape which is more ellipsoidal in regions of high shear and more polygonal in regions of low shear stress. In order to study quantitatively the nature of this response, bovine aortic endothelial cells grown on Thermanox plastic coverslips were exposed to shear stress levels of 10, 30, and 85 dynes/cm2 for periods up to 24 hr using a parallel plate flow chamber. A computer-based analysis system was used to quantify the degree of cell elongation with respect to the change in cell angle of orientation and with time. The results show that (i) endothelial cells orient with the flow direction under the influence of shear stress, (ii) the time required for cell alignment with flow direction is somewhat longer than that required for cell elongation, (iii) there is a strong correlation between the degree of alignment and endothelial cell shape, and (iv) endothelial cells become more elongated when exposed to higher shear stresses.     

血管内皮细胞内皮素代谢的数值分析

将培养的人胚肾小球血管单层内皮细胞置于剪应力分别为6．5dyn/cm^2和13．0dyn/cm^2的定常层流中剪切10小时,样品中的内皮素（ET）分泌量用放射免疫法测定。结果表明,剪切应力和剪切作用时间对内皮细胞内皮素的代谢均有显著的影响,其影响不是简单的线性增减,而呈较复杂的非线性特征,内皮素累积含量和分泌速率,随剪切时间的变化的关系可用Logistic方程来描述,获得了反映内皮素（ET）分泌规律的大量特征方程和特征数,为了解体内发生于血管壁的病理生理过程中内皮素分泌规律提供了实验数据。