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Biomedical subjects

S Chien

Publications and source records attributed to S Chien.

At least 397 records · Page 22Linked to original sources
PubMedDate not supplied

Viscosity of mixtures of sickle and normal red cells at varying hematocrit levels. Implications for transfusion.

Viscosity (eta) in a blood suspension is affected by the total hematocrit (HT) as well as by the deformability of the cells. The impact of these combined factors on the rheologic behavior of sickle cell suspensions and on guidelines for transfusion has not been explored fully. Therefore, the eta of mixtures of washed normal (AA) and sickle (SS) red cells was determined in a rotational viscosimeter as a function of the hematocrit level of SS cells (HS), HT, oxygen tension (PO2), and shear rate. The ratio HT:eta can be taken as an index of potential oxygen delivery. The optimal HT (for maximum HT:eta) became progressively higher as the HS or the HS:HT ratio was lowered: at a given HT, HT:eta rose with a decrease in HS, especially at low HS values. These data support the concept that simple transfusion alone is not as beneficial to the patient as exchange transfusion and that substantial benefit can be obtained by bringing the patient to very low HS levels. The finding that eta rose with HT more steeply when the HS:HT ratio rather than HS was held constant suggested that the absolute level of HS may be more useful than the HS:HT ratio as a guide for a transfusion regimen.

Anemia, Sickle Cell↗
PubMedDate not supplied

Effect of verapamil on splanchnic haemodynamics in a portal hypertensive rat model.

To elucidate the effects of verapamil on splanchnic haemodynamics in rats with portal hypertension, verapamil was given at a low dose (0.2 mg/kg) and a high dose (2 mg/kg) to the rat model after portal vein ligation. Approximately 10% decrease in arterial pressure was caused by the low dose of verapamil, with significant decreases in cardiac output and portal venous inflow as well as reduced portal pressure; these were all indicative of a rise in portal vascular resistance. In contrast, the marked fall in both arterial pressure and cardiac output in the high dose, accompanied by a significant decrease in the portal pressure and the unchanged portal venous inflow, suggested a reduction in portal vascular resistance. This study shows that the acute effects of verapamil on portal hypertension may vary with the dosage used. These results also demonstrate that, since the therapeutic efficacy and safety of verapamil is only in a very limited range of dose, caution should be taken in its clinical use in the treatment of cirrhosis with portal hypertension.

Animals↗
PubMedDate not supplied

Measurement of orientation and distribution of cellular alignment and cytoskeletal organization.

Endothelial cells elongate and align with the direction of applied fluid shear stress. Previously, automated methods for analysis of cell orientation distribution have used Fourier- or fractal-based methods. We used intensity gradients in images of control and sheared endothelial cells to measure orientation distributions. Automated measurements of mean orientation and angular deviation compared favorably with manual measurements. There was a significantly greater angular deviation in images of control cells compared with sheared cells. Automated methods were also used to quantify organization of cytoskeletal fibers using the local angular deviation and a measure of the local coalignment of fibers called the coalignment ratio. The local angular deviation of microtubules and microfilaments was significantly smaller in sheared cells compared with control. The coalignment of cytoskeletal fibers was significantly greater in sheared cells. We conclude that image intensity gradients can be used rapidly, accurately, and objectively to measure cell orientation distributions and cytoskeletal filament organization.

Algorithms↗
PubMedDate not supplied

A strain device imposing dynamic and uniform equi-biaxial strain to cultured cells.

The objective of this study is to design a new apparatus to allow the control of the magnitude and frequency of dynamic stretch applied uniformly to cells cultured on a silicon elastic membrane. The apparatus is designed to produce equi-biaxial dynamic stretches with area changes ranging from 0% to 55% and frequencies ranging from 0 to 2 Hz. Homogeneous finite strain analysis using triangles of markers was performed to compute the symmetric two-dimensional Lagrangian strain tensor on the membrane. Measurements of strain in both static and dynamic conditions showed that the shear component of the strain tensor (Erc) was near zero, and that there was no significant difference between radial (Err) and circumferential (Ecc) components, indicating the attainment of equi-biaxial strain. Bovine aortic endothelial cells were transiently transfected with a chimeric construct in which the luciferase reporter is driven by TPA-responsive elements (TRE). The transfected cells cultured on the membrane were stretched. The luciferase activity increased significantly only when the cells were stretched by 15% or more in area. Cells in different locations of the membrane showed similar induction of luciferase activities, confirming that strain is uniform and equi-biaxial across the membrane.

Animals↗
PubMedDate not supplied

Modeling of molecular mechanisms of cell adhesion.

Cellular adhesion is a process of great importance in biology. We present a simple model of the adhesion process in which the molecular mechanisms involve a receptor, a ligand, and the cytoskeleton of the cell. Based on the energetic consideration of the process, we propose a molecular interpretation of the existing experimental data. The model suggests that the interaction of the receptor and (or) receptor-ligand with the cytoskeleton can have important influence on the formation and strength of the adhesion complex as well as on the subsequent interaction with different ligands. When conformational changes take place during the adhesion process, the characterization of the adhesion bonds based on chemical kinetics alone seems to be incomplete and must be supplemented by parameters, describing the functionality of the complex, i.e., change of the affinity for different ligands, as in the signal transduction, or the strength of the bond, as in the adhesion process.

Cell Adhesion↗
PubMedDate not supplied

Effects of oscillatory mechanical disturbance on macromolecular uptake by arterial wall.

Transport of 125I-albumin by isolated segments of canine common carotid arteries was studied in vitro at zero transmural pressure. Sinusoidal oscillatory variations in length (peak change 4%) for 15 minutes at frequencies of 5 and 10 Hz caused 40% increase in 125I-albumin uptake, and also a 30% increase in the apparent luminal surface area. Changes in the duration and frequency of oscillation indicate that the total number of oscillations (= frequency X duration) was the critical parameter in causing these effects. The increase in apparent luminal surface area was correlated with regional flattening of the internal elastic lamina and the overlying endothelial cells, as demonstrated by transmission and scanning electron microscopy. Endothelial vesicles were counted with the aid of ruthenium red as a postfixation extracellular marker. The ratio of unstained free vesicles to total vesicles averaged 0.083 in the control state and decreased slightly to 0.070 after oscillation. Although the decrease in free vesicle population indicated an acceleration of vesicle diffusion, our theoretical computations showed that the resulting increase in vesicle flux was negligible. The increase in 125I-albumin uptake by the artery following mechanical oscillation is mainly attributable to the increase in apparent luminal surface area.

Animals↗
PubMedDate not supplied

Macromolecular transport across arterial and venous endothelium in rats. Studies with Evans blue-albumin and horseradish peroxidase.

Atherosclerotic lesions are characterized by lipid infiltration in regions with high rates of endothelial cell turnover. The present investigation was designed to elucidate the route of macromolecular transport across vascular endothelium. The aorta and vena cava of male Sprague-Dawley rats were perfusion-fixed after the intravenous injection of Evans-blue albumin (EBA) or horseradish peroxidase (HRP). Fluorescence microscopic examination of en face preparation of the aorta stained with hematoxylin allowed the identification of endothelial cells that underwent mitosis, together with the localization and quantification of fluorescent spots for EBA leakage. The HRP specimens were subjected to histochemical treatment, and HRP leakage was seen as brown spots under the light microscope. Silver nitrate stain was added in both EBA and HRP studies to outline cell boundaries and to visualize stigmata, stomata, and dead cells. In the aorta, almost every dividing cell showed junctional leakage to albumin and HRP, with clustering of leaky spots around the branch orifices. Time-dependent studies showed gradual increases in the diameter and number of these heterogeneously sized leaky spots, which finally fused to sizes corresponding to the "blue areas" for EBA or "brown areas" for HRP. Compared with arteries, veins had fewer mitotic cells, but more dead cells and diffuse dye-staining areas, indicating a more rapid transport of macromolecules. The leaky spots in the artery were associated mainly with mitotic cells, dead cells, and stigmata, whereas those in the vein occurred primarily at regions with dead cells. These results suggest that the preferential association of the enhanced transport of macromolecules with mitosis in the arterial as compared to venous endothelium and the differential behavior in transmural transport between arteries and veins may form the basis for the predilection of atherosclerosis in arteries.

Animals↗
PubMedDate not supplied

Role of dying endothelial cells in transendothelial macromolecular transport.

There are focal areas in the aorta with an enhanced endothelial permeability to macromolecules, as indicated by the focal uptake of the protein-binding azo dye Evans blue in vivo. These areas exhibit high rates of endothelial cell turnover and a number of structural characteristics in en face endothelial morphology. To determine the relationship of endothelial cell death to macromolecular leakage at the level of individual endothelial cells, thoracic aortas of 12 adult male Sprague-Dawley rats were studied at 3 to 5 minutes after intravenous administration of Evans blue-albumin (EBA). Leakage of EBA around individual endothelial cells in en face preparations of the aorta was visualized by fluorescence microscopy. Dying or dead endothelial cells were identified by indirect immunoglobulin G (IgG) immunocytochemistry. Although endothelial cell death is uncommon in normal aortic endothedium (i.e., an average frequency of 0.48%), a high percentage (63%) of IgG-containing dying or dead endothelial cells was found to be associated with EBA leakage. These dying or dead endothelial cells were responsible for 37% of total EBA leaky foci. The results suggest that, in addition to mitotic endothelial cells, the dying or dead endothelial cells also make significant contributions to the local enhancement in aortic endothelial permeability. The present findings lend further support to the "cell turnover-leaky junction" hypothesis for the localization of atherosclerosis.

Albumins↗
PubMedDate not supplied

Endothelial transport of anionized and cationized ferritin in the rabbit thoracic aorta and vasa vasorum.

Transport of anionized ferritins (AF,pl = 3.8-4.2), weakly cationized ferritins (WCF, pI = 7.8-8.1) and cationized ferritins (CF, pI greater than 9.0) was investigated in the rabbit aorta and vasa vasorum. After a 2-minute in situ perfusion, all ferritin species entered luminal vesicles and bound to the luminal endothelial membrane with a high surface density at vesicle necks and regions of cell overlap. In comparison to the aorta, the vasa vasorum had a higher surface density for AF, lower surface densities for CF and WCF, and fewer vesicles containing CF, WCF, or AF. In both types of vessels, vesicle loading of all ferritin species did not agree with a Poisson distribution. After perfusion times of up to 30 minutes, no abluminal vesicles or vasa vasorum endothelium contained CF or WCF; a few abluminal vesicles near cell borders contained AF. In the vasa vasorum, CF and AF entered the subendothelium via occasional fenestrae; AF, but not CF, also permeated the adventitia. Our findings indicate that: 1) binding sites for oppositely charged particles coexist in the same microdomains; 2) the glycocalyces of the vasa vasorum and aorta differ in their relative affinities for oppositely charged particles; 3) vesicular labeling with ferritin is not solely diffusive; and 4) vesicles do not traverse the aortic endothelium under these experimental conditions.

Animals↗
PubMedDate not supplied

Effect of plasma proteins on endothelial binding and vesicle loading of anionized ferritin in rabbit aorta.

Endothelial binding and vesicle loading of anionized ferritin (AF, isoelectric point, 3.8 to 4.2) in plasma and in Tyrode's solution were investigated in the rabbit aorta. After 2 minutes of in situ perfusion, binding to vesicle necks was significantly higher than elsewhere on the membrane and was independent of AF concentration in the range of 0.05 g/ml to 0.2 g/ml for both perfusates. After 30 minutes, no particles were seen in abluminal vesicles and few had reached the basement membrane. Compared to AF in plasma, AF in Tyrode's solution showed lower endothelial binding and greater vesicle loading (p less than 0.005). The average number of particles per loaded vesicle was equal to the average particle density at vesicle necks in Tyrode's solution, but not in plasma, for 0.1 g/ml AF. Gel chromatography and electrophoresis demonstrated no detectable difference between AF particles incubated in plasma or Tyrode's solution. Our experiments indicate that adherence to, or entrapment in, the glycocalyx is an important step for molecules that are transported by vesicles. We hypothesize that plasma proteins adsorb to the endothelial surface and partially shield its net negative charge so that more AF may bind. Plasma proteins also inhibit vesicle loading either sterically or by modifying the electrical potential at the vesicle neck compared to that within the vesicle cavity.

Animals↗
PubMedDate not supplied

Effect of dextran 40 on endothelial binding and vesicle loading of ferritin in rabbit aorta.

The effects of dextran 40 on endothelial binding and vesicle loading of cationized (CF, pl greater than 9.0) and anionic (AF, pl = 3.8 to 4.2) ferritins were investigated in the rabbit aorta. After two minutes of in situ perfusion, both ferritin species entered luminal vesicles and bound to the luminal endothelial membrane with a high surface density at vesicle necks. With CF, the presence of 5% dextran 40 did not change the fraction of vesicles loaded, the number of particles per vesicle, or the average density of particles bound to the luminal membrane, but did reduce the average density of particles adhering to vesicle necks. With AF, dextran 40 increased the percentage of vesicles filled, the average number of particles per loaded vesicle, the membrane particle density, the percentage of loaded vesicle necks, and the average density of particles adhering to vesicle necks. Application of gel chromatography and electrophoresis and determination of carbohydrates in the ferritin and dextran perfusates by the anthrone method after precipitation of the ferritin demonstrated that the dextran and ferritin did not conjugate. We hypothesize that the dextran binds to the endothelial membrane and increases its affinity to AF possibly by shielding negatively charged sites and that it binds in such a way as to offer little steric hindrance to AF particles entering vesicles.

Animals↗
PubMedDate not supplied

Transendothelial transport of low density lipoprotein in association with cell mitosis in rat aorta.

Atherosclerosis is characterized by focal areas of lipid accumulation and intimal smooth muscle cell proliferation in large arteries. In vivo studies on rat aorta with Evans blue-albumin conjugate (EBA) have shown that there are preferential sites of increased permeability with an increased uptake of the conjugate. It has been shown that these blue areas are associated with a high endothelial cell turnover rate and an enhanced permeability to lipids. In a previous study, we demonstrated that 99% of endothelial cells in the mitotic (M) phase as identified by hematoxylin staining of the dividing nuclei exhibited EBA leakage and that these dividing cells accounted for 30% of all leakage sites. In the present study, experiments were performed on the thoracic aortas of 10 adult male Sprague-Dawley rats to determine the statistical frequency of isolated leaks to Lucifer yellow-low density lipoprotein conjugate (LY-LDL) at the level of individual cells and to assess the relationship of such leaks to the cell turnover processes. Leakage of LY-LDL around individual endothelial cells was visualized by fluorescence microscopy, and cells in mitosis on the same specimens were identified by hematoxylin staining. Although endothelial cell mitosis is infrequent (0.034%), 80% of dividing cells in the M phase were associated with LY-LDL leakage. These dividing cells accounted for 45% of all leakage spots. These findings lend support to our recent hypothesis that transiently open junctions surrounding the endothelial cells undergoing cell turnover provide pathways through which LDL enters the subendothelial space, resulting in lipid accumulation.

Animals↗
PubMedDate not supplied

Elevated blood viscosity in patients with borderline essential hypertension.

In patients with borderline hypertension, total peripheral resistance (TPR) is either elevated or abnormally related to cardiac output. Since blood viscosity is one determinant of TPR, we compared various components of blood viscosity in 25 patients with borderline hypertension and 25 normal subjects. Under all experimental blood flow conditions examined, blood viscosity directly correlated with systolic and diastolic blood pressure (p less than 0.05 or better) and was greater in the hypertensive than in normal subjects. Venous hematocrit and plasma viscosity were higher in the hypertensive patients. These latter rheologic abnormalities accounted for the increased blood viscosity at higher shear rates. At lower shear rates, increased red cell aggregation, primarily mediated by elevated fibrinogen concentration, accounted for the higher blood viscosity in the hypertensive subjects. We conclude that even relatively small elevations in arterial pressure are associated with increased viscous resistance of blood to flow, and that the increased blood viscosity is a consequence of increased hematocrit, plasma viscosity, and red cell aggregation.

Adult↗
PubMedDate not supplied

Effects of sphere size and injection site on regional cerebral blood flow measurements.

Regional cerebral blood flows and shunting of microspheres with four different sizes (9,12, 16 and 25 microns) into the superior sagittal sinus were determined in twelve dogs. Venous blood was collected from the superior sagittal sinus for 120 min after the injection of microspheres, and the dogs were then sacrificed immediately. Results on blood flow measurements and venous shunting determinations were similar between left ventricular and left atrial injections. Blood flows measured by 12, 16 and 25 microns spheres were comparable in various brain tissues, except the choroid plexus. 9 microns spheres underestimated blood flows in all regions studied: by 13-19 percent in the cerebral cortex, midbrain, brain stem and cerebellum, by 34-42 percent in the cortical white matter, corpus callosum and cervical cord, and by 64-81 percent in pituitary gland and choroid plexus. These results probably reflect regional difference in microvascular architecture. Venous shunting of 9, 12, 16 and 25 microns spheres during a 24 hr period were 23.6 +/- 2.5, 12.6 +/- 1.2, 4.8 +/- 1.4, and 4.0 +/- 1.2 percent (mean +/- SEM), respectively, with respect to the arterial delivery. Although most of the venous shunting occurred during the first 3 min after the injection of microspheres, it continued 3-60 min after the injection. Beyond 60 min, the venous shunting became minimal for 16 and 25 microns spheres, while significant amount of 9 microns spheres continued to appear in sagittal sinus. This time dependent shunting indicates that some microspheres may be transiently trapped in the microcirculation and become gradually dislodged with time. Failure to consider this time dependence may underestimate the shunting of microspheres through the microcirculation.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMedDate not supplied

Regional cerebral blood flow and oxygen consumption of the canine brain during hemorrhagic hypotension.

The sequential changes in systemic and cerebral hemodynamics, systemic and cerebral oxygen transport and consumption rates, and the regional blood flows (measured with 15 micron microspheres) to the cortical and subcortical brain tissues were determined in nine dogs subjected to graded hemorrhage (10 ml/kg X 4 at 15 min intervals). As hemorrhage progressed, both mean arterial pressure and cardiac output decreased progressively. In contrast to the systemic circulation, the mean cerebral blood flow (mCBF) was well maintained by cerebral vasodilation and the cerebral O2 consumption rate (CMRO2) increased during the first three stages of hemorrhage. At 40 ml/kg of hemorrhage, there were significant reduction in mCBF and CMRO2 despite the increase in O2 extraction, suggesting the occurrence of cerebral hypoxia and decompensation of the cerebral circulation. There were remarkable regional variations in the responses of regional cerebral blood flows (rCBF) to hypovolemia, resulting in a significant redistribution of cerebral blood flow. The fractions of cardiac output supplying the diencephalon (thalamus and hypothalamus), the brain stem (pons and medulla oblongata) and the cervical spinal cord increased after hemorrhage up to 40 ml/kg. The redistribution of rCBF favors those areas where neurons related to cardiovascular control are located. These findings have significant implications relating to hemodynamic regulation during hemorrhagic hypotension.

Animals↗
PubMedDate not supplied

Decrease in cerebral blood flow in rats after experimental subarachnoid hemorrhage: a new animal model.

There continues to be a need for good animal models of experimental subarachnoid hemorrhage (SAH). The rat would be an ideal subject in which to study SAH since it is inexpensive and easier to use than the larger laboratory animals. The present study was undertaken to determine if alterations of cerebral blood flow could be produced in the rat after experimental SAH, and thereby justify using the rat as a model for further study of SAH. Rats weighing between 450 and 500 grams underwent insertion of a cannula into the cisterna magna at least 5 days prior to physiological testing. One group of rats then received a 0.3 cc injection of fresh autologous arterial blood into the cisterna magna to simulate a SAH. Another group of rats received injection of an equal volume of mock CSF (buffered saline) into the cisterna magna. A third group of rats had no subarachnoid injections. In all three groups, blood flow to the cerebral hemispheres was measured with the labeled microsphere technique. Rats with experimental SAH showed a 40% decrease of cerebral blood flow, whereas rats with saline injections showed only a 15% decrease. Control rats had no changes of cerebral blood flow. These studies demonstrate that the rat is a potential experimental model for investigations into SAH.

Animals↗
PubMedDate not supplied

Red cell membrane elasticity as determined by flow channel technique.

The elasticity of red cell membrane was determined in a rectangular flow channel under controlled shear flow. The relation between shear stress and cell extension ratio (lambda) has been analyzed with the use of Evans' two-dimensional model. The deformed cell shapes observed experimentally agreed well with the model with lambda up to 1.4. The best correlation was found at lambda = 1.2. The analysis suggests a nonlinear extensional membrane modulus in the low stress range encountered in the flow channel. In terms of an appropriate strain parameter, the elastic modulus is shown to rise toward the level encountered in micropipette aspiration experiments. The implications of the present findings in modeling of cell mechanics and in cell hemolysis are discussed.

Elasticity↗