Biomedical subjects

K M Jan

Publications and source records attributed to K M Jan.

At least 19 recordsLinked to original sources

PubMed1992

Role of intercellular junctions in the passage of horseradish peroxidase across aortic endothelium.

BACKGROUND: The manner in which molecules are transported across the arterial endothelial layer has been a subject open to much interpretation and controversy. Further elucidation and clarification of these mechanisms are of primary interest. EXPERIMENTAL DESIGN: To investigate the ultrastructural features of arterial endothelial junctions and to evaluate their functional roles as a transendothelial pathway for macromolecular transport, experiments were performed on the thoracic aortae of adult male Sprague-Dawley rats by using the ultrathin serial sectioning technique and horseradish peroxidase (HRP). The aorta was perfusion-fixed with or without prior intravenous injection of HRP. RESULTS: The intercellular clefts exhibited a great deal of variety in shape, being linear, winding, interdigitated, irregular and/or dumbbell-shaped in appearance. Besides the typical 20-nm width encountered at the uniform region of intercellular clefts, local widenings (up to several hundred nm) were quite common. The arterial endothelial junctions were highly organized. Junctional elements, including tight junctions and gap junctions, were frequently present in the same intercellular cleft, even on the same plane of sectioning. Sometimes, gap junctions were found without tight junctions, but the intercellular clefts were rarely obliterated by tight junctions alone. Some intercellular clefts were not obliterated by either gap or tight junctions, and HRP was found to reach the subendothelial space by passing through these junctionless clefts. Densitometric determination of the HRP concentration profile in such junctionless clefts showed a decreasing gradient from the luminal to the abluminal front. The serial sections provided evidence that the apparently free vesicles were actually plasmalemmal membrane invaginations open to the luminal or abluminal front in the arterial endothelium. CONCLUSIONS: The present study showed that the junctionless normal endothelial clefts, in addition to the transiently open junctions surrounding mitotic cells, might provide a significant pathway in the transendothelial transport of macromolecules with the size of HRP.

Animals↗

PubMed1990

Altered rheological properties of blood following administrations of tissue plasminogen activator and streptokinase in patients with acute myocardial infarction.

Tissue blood flow is determined by rheological properties of blood as well as by vascular resistance. In acute myocardial infarction patients who participated in the TIMI I trial, we compared the effects of recombinant tissue plasminogen activator (rt-PA) and streptokinase (SK) on blood rheological properties and plasma fibrinogen concentration. Blood viscosity was determined by using a coaxial cylinder viscometer at shear rates, gamma, of 0.01-200 sec-1. Red blood cell (RBC) deformability was studied by filtration through polycarbonate microsieves with pore size of 3 and 5 microns. Therapy with rt-PA resulted in slight decreases but statistically significant in blood viscosity from 5.2 +/- 0.5 to 4.9 +/- 0.4 cP (gamma = 52 sec-1), plasma viscosity from 1.36 +/- 0.09 to 1.32 +/- 0.06 cP, and plasma fibrinogen from 0.26 +/- 0.04 to 0.21 +/- 0.03 g/dl. SK therapy resulted in reductions in blood viscosity from 5.1 +/- 0.5 to 4.6 +/- 0.3 cP, plasma viscosity from 1.26 +/- 0.10 to 1.16 +/- 0.03 cP, and fibrinogen from 0.26 +/- 0.06 to 0.10 +/- 0.05 g/dl. Changes observed with SK were significantly greater than those observed with rt-PA (all p less than 0.05), and the differences persisted at 10 days after thrombolytic therapy. RBC deformability was similar in the two groups. The greater reduction of blood viscosity after SK than rt-PA suggests that, for a given degree of arterial patency, myocardial blood flow may be better maintained with SK than rt-PA in patients with acute myocardial infarction.

Blood Proteins↗

PubMed1990

Temporal and spatial changes in macromolecular uptake in rat thoracic aorta and relation to [3H]thymidine uptake.

Leaky endothelial junctions associated with cell turnover have been suggested to be a hydrophilic pathway for the transport of macromolecules across the vascular endothelium. To demonstrate focal increases in endothelial permeability, the occurrence of localized uptake of macromolecules in the rat thoracic aorta was studied at various time periods after intravascular administration of Evans blue-albumin (EBA) complexes. With fluorescence microscopy, EBA uptake in the rat thoracic aorta was visible either as discrete spots or as larger areas in both en face and cross-sectional preparations. The average size of EBA leaky spots increased with dye circulation time, indicating that there is a continuous influx of macromolecules through the transiently leaky junctions in these foci with subsequent diffusion in the vessel wall. There was heterogeneity in EBA spot size distribution, suggesting that endothelial cells undergoing turnover in different phases of the cell cycle might exhibit different extents of junctional leakage to macromolecules. The technique of [3H]thymidine labeling autoradiography was applied to en face preparations of the rat thoracic aorta for identifying replicating endothelial cells. The correlation of EBA leakage with [3H]thymidine-labeled endothelial cells was determined. Only 26% of endothelial cells with nuclear incorporation of [3H]thymidine were shown to be associated with EBA leaky foci. This lack of correlation suggests that alterations in endothelial junctional permeability accompanying cell turnover might occur only in some limited time periods of the cell cycle, e.g., the mitotic (M) phase, rather than the whole period of [3H]thymidine labeling.

Albumins↗

PubMed1990

Effect of parathyroid hormone on portal pressure in portal hypertensive rats.

Conflicting results have been common in the pharmacological treatments of portal hypertension. In an attempt to seek better management of portal hypertension, we studied the effect of the synthetic parathyroid hormone (PTH) fragment, [bPTH-(1-34)], in portal hypertensive rats (partial portal vein ligation). PTH, 10 U/kg, administered via the jugular vein resulted in a reduction of both mean arterial blood pressure (MAP) and portal pressure (PP) to a similar extent (18.9% and 16.9%, respectively). A higher dose (40 U/kg) of PTH lowered the PP by 27.8% and MAP by 43.2%. Hemodynamic experiments, performed with labelled microspheres, demonstrated that PTH decreased the blood flow of the splanchnic and hepatic portal collateral vascular beds. To determine whether there is a direct vasodilatory effect on the venous vasculature, the effect of PTH on the isolated portal vein was examined. PTH was capable of inhibiting both spontaneous and drug (methacholine 10(-7) mol/l or KCl 40 mmol/l-induced contraction in a dose-dependent manner. Therefore, it can be assumed that some of the effect of PTH on portal pressure is due to a selective effect on the portal vein.

Animals↗

PubMed1990

Transendothelial macromolecular transport in the aorta of spontaneously hypertensive rats.

Leaky endothelial junctions occurring during cell turnover have been postulated to be a major pathway for enhanced lipoprotein transport across the vascular endothelial layer, which leads to the development of atherosclerosis. Because hypertension has been well documented as one of the major risk factors for atherosclerosis, we explored the possibility that hypertension accelerates atherogenesis by increasing the turnover of endothelial cells and hence the transendothelial macromolecular permeability. The investigations were performed on thoracic aortas of 10 male 3-4-month-old spontaneously hypertensive rats and eight male age-matched Wistar-Kyoto normotensive rats. In en face preparations of aortic specimens, mitotic endothelial cells were identified by hematoxylin nuclear staining; dying or dead endothelial cells containing cytoplasmic immunoglobulin G were detected by indirect immunoperoxidase technique; and endothelial leakage to Evans blue-albumin conjugate was visualized by fluorescence microscopy. The number of leaky foci per unit endothelial surface area in spontaneously hypertensive rats was found to be approximately three times that in Wistar-Kyoto control rats; the frequencies of both endothelial cell mitosis and death in spontaneously hypertensive rats were also approximately three times the corresponding values in Wistar-Kyoto rats. These findings indicate that hypertension in spontaneously hypertensive rats is accompanied by increased endothelial cell turnover and an attendant enhancement of permeability to macromolecules.

Animals↗

PubMed1990

A double isotope technique to determine regional albumin permeability: effects of anesthesia.

The transvascular leakage of albumin in various organs and tissues was studied with a double isotope technique in rats anesthetized with sodium pentobarbital, given intraperitoneally or intravenously, and in unanesthetized (conscious) rats. 125I-labeled albumin and 131I-labeled albumin were injected into the tail vein 1 hr apart. The albumin permeability index in tissues and organs is indicated by the local ratio (Xa/Ya)/(Xb/Yb), where (Xa/Ya) is the ratio of 125I/131I-albumin activities per g of tissue and (Xb/Yb) is the ratio of 125I/131I-albumin activities per g of blood. If there is no passage of albumin across the capillary membrane over the 1-hr period of study, the permeability index will be equal to one. In unanesthetized rats, the liver, lung, kidney, femoral muscle, and femoral skin were regions with a high albumin permeability index (above 2). In these organs, intraperitoneal and intravenous anesthesia caused a decrease or no significant change of the albumin permeability index. There was no significant albumin leakage over 1-hr period (index not significantly different from 1) in the mesentery, abdominal muscle, abdominal skin, cremaster, heart, and brain of unanesthetized rats. Intraperitoneal anesthesia caused the albumin permeability index to increase to approximately 4 in the mesentery, abdominal muscle, and the abdominal skin, but not in the cremaster, heart, or brain. These results demonstrate that pentobarbital anesthesia when given into the peritoneal cavity causes a significant increase in albumin leakage in the abdominal region.

Anesthesia↗

PubMed1990

Effects of blood viscosity on renin secretion.

The effects of alterations in blood and plasma viscosities on plasma renin activity (PRA) were studied in dogs anesthetized with pentobarbital. Blood viscosity was altered by changing the hematocrit (Hct) level by isovolemic exchange using packed red blood cells or plasma. Plasma viscosity was elevated by isovolemic exchange using Hct-matched blood with high molecular weight dextran (Dx, mean m.w. approximately 450,000) dissolved in plasma. Following control measurements of plasma and blood viscosities, plasma [Dx], PRA, Hct and hemodynamic functions, the dog was subjected to isovolemic exchange transfusions to either alter the Hct or administer the Dx. Various measurements were repeated 40-60 min after each exchange. Arterial pressure and renal blood flow remained relatively constant after exchanges; increases in plasma and blood viscosities were accompanied by a decrease in renal vascular hindrance (vasodilation) to keep the renal flow resistance at control level. PRA rose with increases in plasma [Dx] and viscosity, and the rise in PRA was best correlated with the decrease in renal hindrance. The changes in PRA and renal hindrance have the same regression line whether blood viscosity was altered by Hct variation or Dx administration. The results indicate that increases in viscosity cause a compensatory vasodilation of renal vessels to cause renin secretion.

Animals↗

PubMed1989

Effects of dextran-induced hyperviscosity on regional blood flow and hemodynamics in dogs.

In 10 pentobarbitalized dogs, plasma viscosity (Ep) was raised fourfold while apparent blood viscosity (Ea) increased about twofold by two steps of exchange transfusion of 200 ml of plasma with plasma containing high molecular weight dextran (mol wt 500,000, 20% wt/vol). Elevation of Ea was primarily caused by an increase of Ep but not red cell aggregation. As Ea increased, regional blood flow (by 15-microns microspheres) remained constant in most organs but reduced in the small intestine, spleen, and thyroid gland. Vascular hindrance (Z), which reflects the state of vascular geometry, was calculated as flow resistance per Ea. Among various organs, a reduction in Z was noted in the heart, liver, pancreas, kidney, brain, and adrenal gland. In myocardium, there was a progressive reduction of the endocardial-to-epicardial flow ratio, indicating a less profound vasodilation in endocardium than epicardium. These results indicate that dextran-induced hyperviscosity leads to a compensatory vasodilation in several vital organs thus serving to maintain blood flow and nutrient transport.

Animals↗

PubMed1989

Salt-induced hypertension in Dahl salt-sensitive rats. Hemodynamics and renal responses.

This study was performed with Dahl salt-sensitive (DS) and Dahl salt-resistant (DR) rats to detect differences in cardiovascular hemodynamics and renal responses that might be involved in initiating salt-induced hypertension in DS rats. The effects of 4 weeks of 8% NaCl diet were studied in conscious, male DR and DS rats in which vascular and urinary catheters had been previously implanted. Results were compared with those obtained from control groups of DR and DS rats on 4 weeks of 1% NaCl diet. DR rats on 8% salt diet did not develop hypertension, and cardiac output and blood volume were unchanged; glomerular filtration rate, urinary flow, sodium excretion, and plasma atrial natriuretic factor (ANF) increased. DS rats on 8% salt diet developed hypertension, and cardiac output and blood volume increased; glomerular filtration rate, urinary flow, and sodium excretion did not change, despite an increase in ANF. DS and DR rats on 1% NaCl diet were subjected to ANF infusion. After ANF infusion DR rats had a decreased blood volume and an increased glomerular filtration rate, urinary flow, and sodium excretion; DS rats showed no significant changes in blood volume, glomerular filtration rate, urinary flow, or sodium excretion. ANF caused vasodilation in all regions studied in DR rats; DS rats showed vasodilation in all regions except the kidney. After acute volume expansion, although both DR and DS rats responded by an increase in cardiac output, only DS rats developed prolonged hypertension. This finding suggests an inadequate vasodilatory mechanism in DS rats. In response to acute volume expansion, renal resistance decreased in DR rats but not in DS rats. It is concluded that the primary hemodynamic disturbance in DS rats with salt-induced hypertension is an increase in cardiac output caused by blood volume expansion in the absence of any vasodilation. Comparison of the responses of DS and DR rats to high salt diets, ANF infusion, and acute volume expansion indicates that the salt-induced hypertension in DS rats is initiated by a diminished renal response to ANF.

Animals↗

PubMed1989

Shear stress-induced detachment of human polymorphonuclear leukocytes from endothelial cell monolayers.

We employed a static-incubation assay to determine the intensity of wall shear stress (tau) needed to detach human polymorphonuclear leukocytes (HPMNs) from human umbilical vein endothelial cell (HUVE) monolayers. Confluent monolayers of HUVE were placed in a parallel-plate flow chamber which was mounted on the stage of an inverted tissue culture microscope, attached to a perfusion system and maintained at 37 degrees C. All events in the selected fields were recorded using videomicroscopy. HPMNs were co-incubated for 15 minutes with the HUVE monolayers under control conditions or in the presence of 10(-7) M formyl-methionyl-leucyl-phenylalanine (FMLP). Following this static incubation, a series of five individual flows, each 1 minute in duration, were driven through the flow channel, exposing the cells to 1.0, 2.0, 3.8, 7.6 and 14.8 dyn/cm2 wall shear stresses. Under control conditions, the percentage of HPMNs remaining attached to the HUVE monolayers following exposure to each shear stress was 61, 38, 25, 12 and 5, respectively. In the FMLP-treated condition, the percentage of HPMNs remaining attached to the monolayers was significantly greater than control at all five levels of tau. Thus, under control conditions, adherent HPMNs can be detached from endothelial cell monolayers in vitro with levels of shear stress normally found in the microcirculation (18). In the presence of FMLP, the level of shear stress needed to overcome the adhesions is increased significantly.

Cell Adhesion↗

PubMed1988

The role of arterial endothelial cell mitosis in macromolecular permeability.

The present experiments were performed on twelve male Wistar rats to study the quantitative, topographic correlation between transendothelial permeability of Evans Blue-albumin (EBA) conjugate and endothelial cell replication at the single-cell level. En face preparations of the thoracic aorta were examined by fluorescence microscopy. We found a high degree of correlation between endothelial cell mitosis and EBA leaky spots. Although endothelial cell mitosis is very rare in occurrence, nearly all junctions around the dividing cells were leaky (99%), in contrast to only 0.03% of the non-mitotic cells. In addition, electron microscopic observations showed that the junction around a dividing endothelial cell is leaky, whereas that around a dying cell is not. With the aid of our theoretical model, we were able to analyze the dynamics of macromolecular passage through leaky endothelial junctions. The duration of endothelial cell mitosis was estimated to be 67 min, which constituted 0.01% of the duration of the total cell cycle. The time-dependent change in junctional geometry during endothelial cell turnover leads to an inverse relationship between macromolecular size and duration of junctional leakage. For albumin the duration of leakiness across aortic endothelial cell is approximately 3.7 hr. The present findings lend support to our hypothesis that transiently open junctions surrounding the dividing endothelial cells provide the major pathway through which macromolecules enter the subendothelial space to result in lipid accumulation.

Animals↗

PubMed1988

Enhanced macromolecular permeability of aortic endothelial cells in association with mitosis.

Experiments were performed on thoracic aortae of 12 male Sprague-Dawley [corrected] rats to determine the statistical frequency of isolated leaks to Evans blue-albumin (EBA) conjugate at the level of individual cells and to assess the relationship of such leaks to the cell turnover process. Fluorescence microscopy was used to detect leakage of EBA around individual cells, and hematoxylin staining was used to identify cells in mitosis on the same specimens. Although endothelial cell mitosis is very rare in occurrence, 99% of the cells in the M phase were associated with EBA leakage. Since these dividing cells accounted for only one third of all cellular leakage sites, we concluded that significant leakage also occurred in other phases of the cell cycle, probably prior to and after the M phase, or during non-denuding desquamation.

Albumins↗

PubMed1988

Studies on sequestration of neuraminidase-treated red blood cells.

The effects of reduction in the surface charge of red blood cells (RBCs) on regional blood flow and RBC distribution were studied in rats anesthetized with pentobarbital sodium. RBCs were treated with neuraminidase to reduce their electrophoretic mobility by 56%. Normal and neuraminidase-treated RBCs labeled with 51Cr or 111In were injected into a femoral vein while an equal volume of blood was simultaneously withdrawn from a femoral artery. More than 70% of the neuraminidase-treated RBCs injected disappeared from the circulating blood in 30 min compared with less than 2% of normal RBCs. The relative distributions of neuraminidase-treated RBCs to normal RBCs, as determined from radioactivity counting, were significantly greater than 1 in the spleen (5.65 +/- 0.97, mean +/- SD), the liver (2.84 +/- 0.21), the lung (1.48 +/- 0.31), and the kidney (1.49 +/- 0.27), indicating a preferential trapping of neuraminidase-treated RBCs in these regions. This ratio was approximately 1 in all other organs. Regional blood flows in tissues were determined with 15-micron microspheres in the control period and after the infusion of neuraminidase-treated RBCs (experimental). Experimental-to-control blood flow ratios were 0.40 +/- 0.05 in the spleen, 0.66 +/- 0.06 in the liver, 0.78 +/- 0.03 in the lung, and 0.78 +/- 0.09 in the kidneys; this ratio was approximately 1 in all other organs. An experimental-to-control blood flow ratio less than 1 indicates a reduction in blood flow; this occurred in the same organs as those with trapping of neuraminidase-treated RBCs.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1988

Dependence of technetium-99m red blood cell labeling efficiency on red cell surface charge.

The mechanisms by which [99mTc]pertechnetate becomes attached to stannous-primed red blood cells are not known in detail. To study the problem further, the effect of red cell surface charge on labeling efficiency was evaluated. Red cell surface charge was reduced by using the enzyme neuraminidase to remove the terminal charge-bearing sialic acid moiety of the membrane glycoprotein. Forty-five blood samples from six volunteers were treated with neuraminidase for varying lengths of time, resulting in the removal of from 11% to 99% of the normal negative surface charge, as determined from electrophoretic mobility measurements. There was excellent linear correlation between labeling efficiency and the remaining red cell surface charge for values down to 20% of normal (r = 0.89). When surface charge was less than 20% of normal, labeling efficiency was constant at 30%. Eleven blood samples from three donors were divided into two groups that were treated with neuraminidase either before or after they were labeled. The labeling efficiency was independent of the order in which the steps were performed. No evidence for shifting of the radiolabel from the cell membrane to hemoglobin was found. The results suggest that clinical conditions associated with a reduction of sialic acid on the erythrocyte membrane may be one cause of decreased red blood cell labeling efficiency, and that increased membrane permeability for reduced technetium species may be responsible for the decrease.

Adult↗

PubMed1987

Influence of reduced red cell deformability on regional blood flow.

The effects of a reduction in red blood cell (RBC) deformability on regional blood flow and RBC distribution were studied in rats anesthetized with pentobarbital sodium. RBCs were subjected to minimum hardening by incubation in a very diluted solution of glutaraldehyde (0.025%). Normal and partially hardened RBCs, labeled with 51Cr or 111In, were injected into the femoral vein, while an equal volume of blood was simultaneously withdrawn from the femoral artery. Approximately 70% of the labeled, partially hardened RBCs disappeared from the circulating blood within 25 min after injection, compared with less than 2% of the labeled normal RBCs. The relative distribution of RBCs with reduced deformability to normal RBCs in tissues was determined from radioactivity counting; this ratio (mean +/- SD) was 7.95 +/- 0.85 in the spleen, 7.44 +/- 0.43 in the sternum, 7.10 +/- 1.09 in the lung, 4.54 +/- 0.31 in the liver, and 3.50 +/- 0.61 in the femur bone. The results indicate a significant degree of trapping of RBCs with reduced deformability in these regions. This ratio of relative distribution of RBCs with reduced deformability as compared with normal RBCs was 1.06 +/- 0.13 in the heart, indicating the absence of preferential trapping of RBCs with reduced deformability in this organ. Regional blood flows were determined with 15-microns microspheres in the control period and after infusion of RBCs with reduced deformability (experimental).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1986

Effects of blood viscosity on plasma renin activity and renal hemodynamics.

The effects of alterations in apparent blood viscosity on renal hemodynamics and plasma renin activity (PRA) were studied in dogs anesthetized with sodium pentobarbital. Blood viscosity was altered isovolemically either by changes in hematocrit (Hct) or by an increase in plasma viscosity (dextran administration). Arterial blood pressure and renal blood flow (RBF) remained relatively constant when apparent blood viscosity was elevated by changes in Hct or plasma viscosity. Thus the hyperviscosity of blood was associated with a decrease of renal vascular hindrance, resulting in an essentially unchanged renal flow resistance. The decrease in renal vascular hindrance may result from renal vasodilation. In hyperviscosity induced with dextran, the increase in PRA correlates linearly with the decrease in renal vascular hindrance, with a coefficient of correlation of 0.968 (P less than 0.005). The increase in PRA that resulted when Hct was raised from 25 to 55% also can be correlated linearly with the decrease in renal vascular hindrance, with a coefficient of correlation of 0.953 (P less than 0.005). These results suggest that the decrease in renal vascular hindrance in response to a rise in apparent blood viscosity leads to an increase in PRA.

Animals↗

PubMed1986

Roles of surface electrochemistry and macromolecular adsorption in heparin-induced red blood cell aggregation.

Red blood cell (RBC) aggregation in heparin-saline solution was quantified by microscopic observation. The adsorption isotherms of heparin onto normal and neuraminidase-treated RBC surfaces were determined by radioactive heparin labeled with 125I-Bolton-Hunter Reagent. RBC aggregation by heparin requires the presence of sialic acids at cell surface and was enhanced by reduction of ionic strength of the suspending medium. Adsorption of heparin onto RBC surface was increased by removal of sialic acids. These findings not only serve to elucidate the basic mechanism of cell-cell interaction mediated by negatively charged macromolecules, but also provide experimental evidence for the possible conformational change of macromolecules at the charged surface.

Adsorption↗

PubMed1985

Distribution of myocardial stress and its influence on coronary blood flow.

The myocardial stress was analyzed by biomechanical modeling in correlation with experimental findings. The pressure-volume relationship follows the stress-strain relationship of muscle fibers. From the knowledge of fiber orientation and the distribution of sarcomere length, the myocardial stress components including fiber, longitudinal, circumferential and radial stresses were expressed as a function of fraction of wall thickness. The coronary blood flow is influenced by the myocardial radial stress. With the use of vascular waterfall theory, it is possible to correlate the theoretically defined stress distribution with experimentally obtained stress distribution. An elevation of radial stress in myocardium causes a reduction of vessel patency. During both systole and diastole, vessel patency remains constant at epicardium. At endocardium, however, vessel patency undergoes rhythmic changes following the systolic and diastolic influences of the radial stress. The physiological implication is that during systole, the endocardium suffers low blood flow and this transient ischemic state requires compensatory replenishment from diastolic perfusion. Such phenomena become less apparent toward the epicardium.

Biomechanical Phenomena↗