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At least 865 records · Page 48Linked to original sources
PubMed1986

Increase in fluid viscosity during epididymal transit and the immobilization of rat epididymal spermatozoa.

A microcapillary method was developed to measure the viscosity of small volumes of undiluted epididymal fluid. Fluid from the cauda epididymis registered 82 +/- 17 centipoise which was much more viscous than fluid from the caput region (8 +/- 2 centipoise). Initiation of sperm motility was strongly suppressed in the viscosity range of 7 to 150 centipoise. A significant increase in the viscosity of fluid from the caput region was observed when immobilin in the fluid binds with a lectin from Jack fruit (Artocarpus heterophyllus). Thus, it is postulated that aggregation of the immobilin induced by a lectin-like material produced by the cauda epididymis may be a mechanism by which fluid viscosity is increased during epididymal transit.

Animals↗
PubMed1983

The influence of cholesterol incorporation and removal on lipid-bilayer viscosity and electron transfer in rat-liver microsomes.

The incorporation and removal of cholesterol from rat liver microsomes was used as a methodical approach to investigate the molecular organization of microsomal redox-chains. It was shown that the incorporation of cholesterol in microsomes increases and removal of cholesterol decreases lipid bilayer viscosity as indicated from the rate of fluorescent probe-pyrene eximerisation in cholesterol-enriched and cholesterol-depleted microsomes. The increase of membrane viscosity slows down the initial rates and decreases the rate constants of cytochrome b5 reduction by NAD(P)H, whereas the decrease of membrane viscosity enhances the initial rates and increases the rate constants of these reactions. The rates of cytochrome P450 reduction by reduced pyridine nucleotides do not depend on the viscosity of lipid bilayer. The incorporation and removal of cholesterol from microsomes was not followed by any essential changes in the rates of dimethylaniline N-demethylation, aniline p-hydroxylation, p-nitroanisole O-demethylation, oxygen consumption, oxidation of NADH and NADPH. Thus the reduction of cytochrome b5 by NADH and NADPH is the diffusion-dependent reaction in the redox-chains of microsomes only.

Animals↗
PubMed1991

Conformational dynamics and solvent viscosity effects in carboxypeptidase-A-catalyzed benzoylglycylphenyllactate hydrolysis.

We have used a new approach to the dynamics of hydrolytic metalloenzyme catalysis based on investigations of both external solvent viscosity effects and kinetic 2H isotope effects. The former reflects solvent and protein dynamics, and the nuclear reorganization distribution among damped protein motion and intramolecular friction-free nuclear motion. The isotope effect represents proton tunnelling and reorganization in the hydrogen bond network around the active site. We illustrate the approach by new spectrophotometric and pH-titration data for carboxypeptidase-A-catalyzed benzoylglycyl-L-phenyllactate hydrolysis. This substrate exhibits both a significant inverse fractional power law viscosity dependence over wide ranges controlled by glycerol and sucrose, and a kinetic 2H isotope effect of 1.65. The analogous benzoylglycylphenylalanine hydrolysis has a smaller isotope effect (1.3) and no viscosity dependence. Viscosity variation has no effect on the CD spectra in the 180-240-nm range. In terms of stochastic chemical rate theory, the data correspond to an enzyme-peptide substrate complex with a 'tight' structure protected from the solvent. In comparison, the enzyme-ester substrate complex is 'softer', strongly coupled to the solvent, and the rate-determining step is accompanied by proton transfer or by substantial reorganization in the hydrogen bonds near the active site.

Carboxypeptidases↗
PubMed2005

Effects of enhanced viscosity on canine gastric and intestinal motility.

BACKGROUND AND AIM: The aim of this study was to investigate the effect of enhanced viscosity on gastric emptying and gastrointestinal motor and myoelectrical activities in dogs. METHOD: The study was performed in eight healthy female hound dogs chronically implanted with four pairs of gastric and two pairs of intestinal serosal electrodes and a duodenal fistula. Each dog was studied in three sessions and fed with three test meals with different viscosity. Gastric emptying was monitored for 2 h simultaneously with gastric and intestinal myoelectrical recordings. RESULTS: The liquid test meal containing either 0.78% or 1.21% of galactomannan significantly delayed gastric emptying but had no effect on postprandial blood glucose levels in comparison with the meal containing no galactomannan. The liquid test meal containing either 0.78% or 1.21% of galactomannan significantly increased the frequency and strength of intestinal motility but had no effect on intestinal slow wave rhythms. The product with enhanced viscosity had no effect on gastric motor activity or gastric slow waves. CONCLUSION: It was concluded that enhanced viscosity delays gastric emptying, increases postprandial intestinal but not gastric motility, and has no effects on gastric or intestinal slow waves.

Animal Feed↗
PubMed1991

The effects of diet and insulin therapy on coagulation factor VII, blood viscosity, and platelet release proteins in diabetic patients with secondary sulphonylurea failure.

The effect of intensified dietary measures and subsequently insulin therapy upon haemorheological measures were studied in Type 2 diabetic patients with secondary sulphonylurea failure. Coagulation factors VIIc and VIIIc, fibrinogen, plasma viscosity, whole blood viscosity, beta-thromboglobulin, platelet factor 4, von Willebrand factor, and euglobulin clot lysis time were measured at baseline, after 3 months intensified dietary therapy and after 4 months insulin therapy. During intensified dietary therapy there was a significant fall in serum cholesterol (p less than 0.05) and a small decrease in weight, but no significant change in blood glucose control. Factor VIIc levels fell significantly (1.22 (SE 0.07) vs 1.42 (0.08) u ml-1, p less than 0.01), and plasma viscosity and whole blood viscosity (23 s-1) also improved (both p less than 0.05). Insulin therapy was instituted with either continuous subcutaneous insulin therapy or twice daily injections of soluble and isophane (NPH) insulin. During this period glycosylated haemoglobin improved (mean (SE) 49.5 (1.4) vs 65.0 (2.1) mmol-HMF mol-Hb-1, p less than 0.001; normal range 29-39 mmol-HMF mol-Hb-1) as did serum triglyceride (p less than 0.01), but weight increased (p less than 0.001). The only haemorheological changes with insulin were increased levels of the platelet release proteins beta-thromboglobulin (37 (3) vs 28 (2) micrograms l-1, p less than 0.01) and platelet factor 4 (median 7.5 (range 3.0-18.0) vs 4.5 (2.0-10.5) micrograms l-1, p less than 0.01).

Adult↗
PubMed1988

Impression materials: effect of hydrophilicity and viscosity on ability to displace water from dentin surfaces.

The water-displacing ability of hydrophilic and hydrophobic impression materials was determined and related to the hydrophilicity and viscosity of the materials. The water-displacing ability of the materials was determined on a network of grooves in a dentin surface covered by a drop of water. After setting of the material, the number of crossings reproduced in the impression was calculated in percent of the total number of crossings. The hydrophilicity was assessed by measuring the contact angle between water and impression material. To determine viscosity, a rotoviscosimeter was used. Impression materials with contact angles less than 70 degrees showed a significant negative correlation between water-displacing ability and contact angle, i.e. the reproducing ability decreased with decreasing hydrophilicity of the materials. Impression materials with contact angles above 70 degrees showed a significant positive correlation between water-displacing ability and viscosity, i.e. the water-displacing ability improved with increasing viscosity.

Chemical Phenomena↗
PubMed1992

In vivo measurement of leukocyte viscosity during capillary plugging.

Leukocyte plugging of capillaries in vivo was measured in rat spinotrapezius muscle. The plug durations, leukocyte and capillary dimensions, and arteriolar pressure at the plug sites were applied to the mechanical model of Needham and Hochmuth (1990) to estimate the leukocyte viscosities. The viscosity distribution of 389 cells was lognormal with a median value of 232 Poise. 3.1 percent of the cells were apparently activated and displayed viscosities greater than 3000 Poise. The median viscosity suggests that inactivated leukocytes have a minimal effect on blood flow, but that leukocyte activation may result in significant increases in microvascular flow resistance.

Animals↗
PubMed1996

Effect of viscosity on swimming by the lateral and polar flagella of Vibrio alginolyticus.

By using mutants of Vibrio alginolyticus with only a polar flagellum (Pof+ Laf-) or only lateral flagella (Pof- Laf+), we examined the relationship between swimming speed and the viscosity of the medium for each flagellar system. Pof+ Laf- cells could not swim in the high-viscosity environment (ca. 200 cP) in which Pof- Laf+ cells swam at 20 microns/s. The Pof- Laf+ cells swam at about 20 microns/s at normal viscosity (1 cP) without the viscous agent, and the speed increased to 40 microns/s at about 5 cP and then decreased gradually as the viscosity was increased further. These results show the functional difference between polar and lateral flagella in viscous environments.

Cell Movement↗
PubMed2002

Trehalose-mediated inhibition of the plasma membrane H+-ATPase from Kluyveromyces lactis: dependence on viscosity and temperature.

The effect of increasing trehalose concentrations on the kinetics of the plasma membrane H+-ATPase from Kluyveromyces lactis was studied at different temperatures. At 20 degrees C, increasing concentrations of trehalose (0.2 to 0.8 M) decreased V(max) and increased S(0.5) (substrate concentration when initial velocity equals 0.5 V(max)), mainly at high trehalose concentrations (0.6 to 0.8 M). The quotient V(max)/S(0.5) decreased from 5.76 micromol of ATP mg of protein(-1) x min(-1) x mM(-1) in the absence of trehalose to 1.63 micromol of ATP mg of protein(-1) x min(-1) x mM(-1) in the presence of 0.8 M trehalose. The decrease in V(max) was linearly dependent on solution viscosity (eta), suggesting that inhibition was due to hindering of protein domain diffusional motion during catalysis and in accordance with Kramer's theory for reactions in solution. In this regard, two other viscosity-increasing agents, sucrose and glycerol, behaved similarly, exhibiting the same viscosity-enzyme inhibition correlation predicted. In the absence of trehalose, increasing the temperature up to 40 degrees C resulted in an exponential increase in V(max) and a decrease in enzyme cooperativity (n), while S(0.5) was not modified. As temperature increased, the effect of trehalose on V(max) decreased to become negligible at 40 degrees C, in good correlation with the temperature-mediated decrease in viscosity. The trehalose-mediated increase in S(0.5) was similar at all temperatures tested, and thus, trehalose effects on V(max)/S(0.5) were always observed. Trehalose increased the activation energy for ATP hydrolysis. Trehalose-mediated inhibition of enzymes may explain why yeast rapidly hydrolyzes trehalose when exiting heat shock.

Adenosine Triphosphate↗
PubMed1983

Abnormal blood viscosity and haemostasis in long-standing retinal vein occlusion.

Blood viscosity and several haemostatic factors were measured in 42 patients with long-standing retinal vein occlusion and 33 control subjects. Blood viscosity, haematocrit, plasma viscosity, fibrinogen, fibrinopeptide A, and beta-thromboglobulin were increased in the 20 subjects with capillary nonperfusion or new vessels, but not in the 22 subjects without these complications. Patients with nonperfusion or new vessels also had a lower platelet count than patients without complications. Increased levels of factor VIII antigen and decreased levels of antithrombin III were found in the retinal vein occlusion group as a whole. These findings suggest that blood viscosity, platelets, and coagulation may be involved in retinal vein occlusion and its vascular complications.

Aged↗
PubMed1996

Blood viscosity, coagulation, and activated protein C resistance in central retinal vein occlusion: a population controlled study.

BACKGROUND: The role of blood viscosity and haemostasis has been investigated in mixed groups of patients with branch and central retinal vein occlusion (CRVO) with conflicting results. This may have partly been due to the different aetiologies of these two types of vein occlusion. METHODS: In this study viscosity and coagulation (including activated protein C resistance) were examined in 87 patients with CRVO and compared with the results from an age-matched, population based control group. RESULTS: Viscosity variables were higher in CRVO than in controls which suggested that reduced red cell deformability was associated with the occurrence of CRVO. A higher percentage of the patients with CRVO (12%) had activated protein C resistance than controls (5%). Patients who developed the complication of iris neovascularisation had relatively low antithrombin III, factor VII, and tissue plasminogen activator indicating both a tendency to thrombus formation and a reduction in fibrinolytic activity. CONCLUSION: Increased blood viscosity may contribute to the production of CRVO by inducing stasis of blood flow, with thrombus formation in at risk individuals who go on to develop iris neovascularisation.

Adult↗
PubMed1971

Influence of blood viscosity on blood flow and the effect of low molecular weight dextran.

Changes in whole blood viscosity are related to changes in the leg blood flow during infusions of low-molecular-weight dextran and Hartmann's solution. A close inverse correlation exists between changes in viscosity and blood flow, the change in blood flow being about three times greater than the change in blood viscosity. The dextran and Hartmann's solution had a similar effect on blood viscosity and blood flow if corrections are made for the difference in haemodilution.

Blood Flow Velocity↗
PubMed1995

Helicobacter pylori infection does not reduce the viscosity of human gastric mucus gel.

The mechanism by which Helicobacter pylori undermines host defence mechanisms is unclear. Several in vitro studies using soluble mucins have suggested that H pylori may compromise mucus function. Gastric mucus gel was obtained from 13 H pylori infected patients; six untreated subjects and seven after eradication of the infection. Gastric mucus is a non-Newtonian substance in that its viscosity changes with changing rates of shear, requiring mucus viscosity to be measured in a rotational cone-plate microviscometer. Viscosity was measured at shear rates varying from 1.15 s-1 to 46 s-1. The gastric mucus viscosity was significantly higher in patients infected with H pylori compared with mucus gel obtained after eradication of the infection. The results of our study suggest that the previous studies using in vitro methods involving soluble mucins or its components may have lead to erroneous conclusions about the in vivo interactions of H pylori and gastric mucus gel. The present findings argue against the hypothesis that degradation of gastric mucus by H pylori is important in the pathogenesis of peptic ulcer.

Female↗
PubMed1977

A comparison of the erythrocyte sedimentation rate and plasma viscosity in detecting changes in plasma proteins.

The Westergren erythrocyte sedimentation rate (ESR) and plasma viscosity were compared in 114 patients and their correlations with total and differential plasma protein fractions were analysed. There is a linear correlation between these two screening tests. Higher correlation coefficients were obtained between the plasma viscosity and fibrinogen and alpha and gamma globulins than with the ESR. Albumin affected the two tests in opposite directions. The ESR was falsely increased by a fall in haemoglobulin even within two standard deviations from the mean. Both tests gave an appreciable number of incorrect values--the plasma viscosity in 21 cases and the ESR in 33. The cause for these is discussed. It is concluded that the plasma viscosity is the more sensitive and reliable measure of changes in acute phase protein reactants and more useful for monitoring clinical progress.

Alpha-Globulins↗
PubMed1976

Frothy feedlot bloat in cattle: production of extracellular polysaccharides and development of viscosity in cultures of Streptococcus bovis.

Streptococcus bovis was cultured in a synthetic medium with three concentrations of sucrose. Initial viscosity of the media was 1.5 centipoise (cp). After incubation for 8 h, the viscosity of the medium with 0.5% sucrose was unchanged, that with 3% sucrose had increased to 8 cp, and that with 6% sucrose to 112 cp. Similar results were found with a rumen fluid medium. A slimy material, responsible for increased viscosity of these cultures, was digested by dextranase. The material appeared as a complex system of intercellular fibers when viewed under the electron microscope after freeze-etching. With proteins and other polymers released from lysed bacteria, this slimy material may contribute directly to increased viscosity and foam formation. In addition to these intercellular fibers, each cell was surrounded by a fibrous capsule that was not digested by dextranase. This capsule stained with lead citrate and uranyl acetate, but not with ruthenium red. The amount of capsular material produced was similar whether the media contained 0.5, 3.0, or 6% sucrose.

Anaerobiosis↗
PubMed1992

Organic osmolytes increase cytoplasmic viscosity in kidney cells.

The hypothesis was tested that accumulation of osmolytes by kidney cells grown in hyperosmolar media decreases the rotational and translational mobilities of small polar solutes in the cytosolic compartment. Rotational mobility was measured by the picosecond rotational correlation times (tau c) of 2',7'-bis(2-carboxyethyl)-5(6)carboxylfluorescein (BCECF) by multiharmonic microfluorimetry. In isolated segments of rabbit proximal tubule, thick ascending limb, and cortical collecting duct that were perfused and bathed in 300 mosM media, tau c were in the range 180-250 ps, corresponding to apparent rotational viscosities (eta r) of 1.1-1.5 cP. In cortical collecting tubule, eta r was not influenced by serosal vasopressin. In Madin-Darby canine kidney (MDCK) cells grown in 300-1,200 mosM media, eta r increased progressively by up to a factor of 1.38 +/- 0.03; measurements of tau c and macroscopic viscosity in artificial solutions containing osmolytes supported the hypothesis that the increased eta r was due to accumulation of organic osmolytes. BCECF translational mobility was measured by fluorescence photobleaching recovery using a focused 1.2-microns diameter Ar laser beam at 488 nm. Recovery half-times were 36 +/- 3 (SE) ms (n = 10) in MDCK cells grown in 300 mosM media and 62 +/- 3 ms (n = 10) when grown in 1,200 mosM media. The results suggest that accumulation of osmolytes by renal cells is associated with significantly increased cytosolic viscosity. The increased viscosity would slow enzymatic and transport processes in the cytosolic compartment.

Animals↗
PubMed1991

Profound increase in viscosity and aggregation of pig gastric mucin at low pH.

Epithelial mucins are glycoproteins of very large molecular weight that provide viscoelastic and gel-forming properties to mucus, the jellylike protective layer covering epithelial organs. In the mammalian stomach the mucus gel layer protects the underlying epithelial cells from HCl in the lumen. We report here that pig gastric mucin undergoes a 100-fold increase in viscosity in vitro when pH is lowered from 7 to 2. Sedimentation velocity and dynamic light-scattering measurements revealed the formation of extremely large aggregates at low pH consistent with the observed increase in viscosity. Aggregation of mucin at low pH was prevented by increasing the ionic strength, suggesting the involvement of electrostatic interactions. Trypsin digestion and thiol reduction, but not enzymatic removal of neuraminic acid, prevented aggregation at low pH. This implies that the peptide core rather than the oligosaccharide side chains of the molecule is involved in the aggregation of mucin at low pH. Increased aggregation and viscosity at low pH were also observed in a solvent made to mimic the ionic composition of gastric juice, indicating the physiological relevance of our findings. Our observations suggest that one mechanism of gastric protection may be the ability of gastric mucin to undergo aggregation with a marked increase in viscosity at low pH.

Animals↗
PubMed2004

Elevated plasma viscosity in extreme hemodilution increases perivascular nitric oxide concentration and microvascular perfusion.

We tested the hypothesis that high-viscosity (HV) plasma in extreme hemodilution causes wall shear stress to be greater than low-viscosity (LV) plasma, leading to enhanced production of nitric oxide (NO). The perivascular concentration of NO was measured in arterioles and venules and the tissue of the hamster chamber window model, subjected to acute extreme hemodilution, with a hematocrit (Hct) of 11% using Dextran 500 (n = 6) or Dextran 70 (n = 5) with final plasma viscosities of 1.99 +/- 0.11 and 1.33 +/- 0.04 cp, respectively. HV plasma significantly increased the periarteriolar, perivenular, and tissue NO concentration by 2.0, 1.9, and 1.4 times the control (n = 7). The NO concentration with LV plasma was not statistically different from control. Arteriolar shear stress was significantly increased in HV plasma relative to LV plasma in arterioles but not in venules. Aortic endothelial NO synthase (eNOS) protein expression was increased with HV plasma but not with LV plasma. There was a weak correlation between perivascular NO concentration and the locally calculated shear stress induced by the procedures, when blood viscosity was corrected according to Hct values previously determined in studies of microvascular Hct distribution. The finding that the periarteriolar and venular NO concentration in HV plasma was the same although arteriolar shear stress was significantly greater than venular shear stress maybe be due to differences in vessel wall metabolism between arterioles and venules and the presence of NO transport through the blood stream in the microcirculation. Results support the concept that in extreme hemodilution HV plasma maintains functional capillary density through a NO-mediated vasodilatation.

Animals↗