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PubMed2000

Association of plasma viscosity and carotid thickening in a French working cohort.

Plasma viscosity and intima-media thickness (IMT) are frequently associated with cardiovascular disease and its risk factors. We evaluated the association of rheologic and vascular factors in asymptomatic subjects. Plasma viscosity (coaxial cylinder viscometry) and both preintrusive and intrusive atherosclerosis in the carotid arteries (ultrasonography) were investigated in 246 men and 337 women aged 17 to 65 years from the AXA study, a prospective cohort of healthy workers. Plasma viscosity was positively related to age-adjusted mean bifurcation carotid artery IMT (P < .01 for men; P < .04 for women) and maximum carotid artery IMT (P < .01 for men; P < .02 for women), but not to mean common carotid artery IMT. Multivariate adjustment affected these relations to a greater extent in men than in women. The odds ratio (range) of having intrusive atherosclerosis in relation to 1 SD greater plasma viscosity was 2.27 (1.52 -3.38) in men and 1.63 (1.17-2.26) in women. Adjustment of age, waist-to-hip ratio, smoking, hypercholesterolemia, hypertension, diabetes, and fibrinogen had very little effect on the magnitude of these odds ratios. Thus, plasma viscosity was associated with carotid thickening, suggesting that rheologic factors are involved in the subclinical phase of atherosclerosis.

Adolescent↗
PubMed2001

New fluorescent probes for the measurement of cell membrane viscosity.

BACKGROUND: Molecular rotors are fluorescent molecules that exhibit viscosity-dependent fluorescence quantum yield, potentially allowing direct measurements of cell membrane viscosity in cultured cells. Commercially available rotors, however, stain not only the cell membrane, but also bind to tubulin and migrate into the cytoplasm. We synthesized molecules related to 9-(dicyanovinyl)-julolidine (DCVJ), which featured hydrocarbon chains of different length to increase membrane compatibility. RESULTS: Longer hydrocarbon chains attached to the fluorescent rotor reduce the migration of the dye into the cytoplasm and internal compartments of the cell. The amplitude of the fluorescence response to fluid shear stress, known to decrease membrane viscosity, is significantly higher than the response obtained from DCVJ. Notably a farnesyl chain showed a more than 20-fold amplitude over DCVJ and allowed detection of membrane viscosity changes at markedly lower shear stresses. CONCLUSIONS: The modification of molecular rotors towards increased cell membrane association provides a new research tool for membrane viscosity measurements. The use of these rotors complements established methods such as fluorescence recovery after photobleaching with its limited spatial and temporal resolution and fluorescence anisotropy, which has low sensitivity and may be subject to other effects such as deformation.

Cell Membrane↗
PubMed1998

Nonionic compact dimers: a new generation of isosmolar iodinated contrast media with low viscosity.

RATIONALE AND OBJECTIVES: The authors evaluated compact dimers, a new class of molecule designed to reduce the osmolality of concentrated solutions of x-ray contrast media without increasing their viscosity. MATERIALS AND METHODS: Molecular modeling was used to design a new hexaiodo dimeric structure with low viscosity and good shielding of hydrophobic areas. This design ends in the synthesis of different prototypes, the structure of which was characterized by a single bond between two perpendicular rings and the presence of tertiary amides. The validity of this approach was investigated with measurements of physicochemical properties (viscosity, osmolality, logP) and pharmacologic studies (urinary and biliary excretion, intravenous and intracerebral medial lethal dose). RESULTS: Solutions of the compact dimers at a concentration of 350 mg of iodine per milliliter combine osmolalities that are close to that of blood with viscosities at ambient temperature nearly half those of commercially available dimers. Furthermore, these new compounds have a tolerance level comparable with that of currently used nonionic media (intravenous median lethal dose, > 17.5 g of iodine per kilogram). CONCLUSION: The three-dimensional structure of the compact dimers has made it possible to control both physicotoxicity and chemotoxicity by combining isotonicity and low viscosity with good tolerance.

Animals↗
PubMed2006

No effect of increased water intake on blood viscosity and cardiovascular risk factors.

Observational data have suggested that increased water intake decreases the risk of CHD. A postulated mechanism is that increased water ingestion reduces blood viscosity. The aim of the present study was to assess the effect of increased fluid intake on blood viscosity. Men (n 67) and postmenopausal women (n 27) with one or more risk factors for CVD who reported intake of < or =0.5 litres water daily were randomised to a control group (n 31), an intervention group (n 32) that increased their daily water intake by 1 litre/d and an intervention group (n 31) that ingested 1 litre blueberry juice/d. All were encouraged to continue their usual diet and lifestyle. Whole-blood viscosity and blood and urine chemistries were measured by standard techniques after 2 and 4 weeks. Urine volume increased (by a median of 872 and 725 ml in the water and blueberry juice groups, respectively, v. 10 ml in the control group; P< or =0.002), confirming the subjects' adherence to the protocol. Urine osmolality and urinary levels of Na, K and creatinine decreased in the water and blueberry juice groups v. the controls (P<0.05). No change was seen in whole-blood viscosity or in levels of fibrinogen, total protein, lipids, glucose, insulin, C-peptide or other chemistry and haematology variables. In conclusion, a postulated protective effect of increased water or fluid intake is not explained by a change in blood viscosity and increased fluid intake does not influence CVD risk factors in the short term.

Adult↗
PubMedDate not supplied

Prediction of the viscosity radius and the size exclusion chromatography behavior of PEGylated proteins.

Size exclusion chromatography (SEC) was used to determine the viscosity radii of equivalent spheres for proteins covalently grafted with poly(ethylene glycol) (PEG). The viscosity radius of such PEGylated proteins was found to depend on the molecular weight of the native protein and the total weight of grafted PEG but not on PEG molecular weight, or PEG-to-protein molar grafting ratio. Results suggest grafted PEG's form a dynamic layer over the surface of proteins. The geometry of this layer results in a surface area-to-volume ratio approximately equal to that of a randomly coiled PEG molecule of equivalent total molecular weight. Two simple methods are given to predict the viscosity radius of PEGylated proteins. Both methods accurately predicted (3% absolute error) the viscosity radii of various PEG-proteins produced using three native proteins, alpha-lactalbumin (14.2 kDa MW), beta-lactoglobulin dimer (37.4 kDa MW), and bovine serum albumin (66.7 kDa MW), three PEG reagents (2400, 5600, and 22500 MW), and molar grafting ratios of 0 to 8. Accurate viscosity radius prediction allows calculation of the distribution coefficient, K(av), for PEG-proteins in SEC. The suitability of a given SEC step for the analytical or preparative fractionation of different PEGylated protein mixtures may therefore be assessed mathematically. The methods and results offer insight to several factors related to the production, purification, and uses of PEGylated proteins.

Chromatography, Gel↗
PubMed1987

Enzyme kinetics in solvents of increased viscosity. Dynamic aspects of carbonic anhydrase catalysis.

The dependence of enzymatic catalysis on diffusion rates in solution was examined with regard to high specific activity carbonic anhydrase (CA II) by varying the viscosity of the reaction medium with added glycerol, sucrose, and ficoll (a copolymer of sucrose and epichlorohydrin). Responses of the Michaelis-Menten parameters associated with CO2 hydration and HCO3- dehydration were deduced and analyzed by utilizing a spectrophotometric stopped-flow technique. It was found that both kcatHCO3 (= 3.9 X 10(5) s-1 at pH 5.90) and kcatCO2 (= 1.2 X 10(5) s-1 at pH 5.90 and 8.6 X 10(5) s-1 at pH 8.80) steadily decreased with the addition of monomeric viscogen while both KmHC03- (= 20 mM at pH 5.90) and KmCO2 (= 18 mM at pH 5.90 and 13 mM at pH 8.80) remained independent of viscosity, within experimental error. These results indicate that some kind of proton-transfer-related event is primarily responsible for the observed rate decrease. The three polyhydroxy cosolutes exhibited significant differences with regard to the magnitude of the viscosity effect on the kcat of the enzyme, with glycerol affecting the largest decrease, sucrose affecting a moderate one, and ficoll having virtually no effect. The discrepancy between glycerol and sucrose could be largely reconciled by correcting for diffusion-unrelated effects as estimated from rate studies of considerably slower CA II catalyzed acetaldehyde hydration and p-nitrophenyl acetate hydrolysis. Ficoll, however, was found to be unsuitable as a viscogenic probe because it failed to appreciably decrease the mobilities of smaller ions (as deduced from electrolytic conductance measurements) despite its capacity to greatly increase the macroscopic viscosity of the medium. Our best estimates indicate that this reaction comes within ca. 30% of the diffusion limit at 0.890 cP and 25 degrees C for both CO2 hydration and HCO3- dehydration reactions. However, it is reasonable to expect this value to be considerably higher in the natural environment of the enzyme because of the relatively high viscosities attained in the interior of erythrocytes.

Acetaldehyde↗
PubMed2002

Effect of solution viscosity on intramolecular electron transfer in sulfite oxidase.

Our previous studies have shown that the rate constant for intramolecular electron transfer (IET) between the heme and molybdenum centers of chicken liver sulfite oxidase varies from approximately 20 to 1400 s(-1) depending upon reaction conditions [Pacheco, A., Hazzard, J. T., Tollin, G., and Enemark, J. H. (1999) J. Biol. Inorg. Chem. 4, 390-401]. These two centers are linked by a flexible polypeptide loop, suggesting that conformational changes, which alter the Mo-Fe distance, may play an important role in the observed IET rates. In this study, we have investigated IET in sulfite oxidase using laser flash photolysis as a function of solution viscosity. The solution viscosity was varied over the range of 1.0-2.0 cP by addition of either polyethylene glycol 400 or sucrose. In the presence of either viscosogen, an appreciable decrease in the IET rate constant value is observed with an increase in the solvent viscosity. The IET rate constant exhibits a linear dependence on the negative 0.7th power of the viscosity. Steady-state kinetics and EPR experiments are consistent with the interpretation that viscosity, and not other properties of the added viscosogens, is responsible for the dependence of IET rates on the solvent composition. The results are consistent with the role of conformational changes on IET in sulfite oxidase, which helps to clarify the inconsistency between the large rate constant for IET between the Mo and Fe centers and the long distance (approximately 32 A) between these two metal centers observed in the crystal structure [Kisker, C., Schindelin, H., Pacheco, A., Wehbi, W., Garnett, R. M., Rajagopalan, K. V., Enemark, J. H., and Rees, D. C. (1997) Cell 91, 973-983].

Animals↗
PubMedDate not supplied

Dependence of apparent viscosity on mycelial morphology of Streptomyces fradiae culture in various nitrogen sources.

To examine what causes increased viscosity in culture broth in Streptomyces fradiae culture, various natural nitrogen sources were investigated. Extracellular protease activity increased with culture time and decomposed the natural nitrogen source into amino acids. In the case of gluten meal, after a culture time of 5 d, concentrations of glutamic acid and aspartic acid had increased to 600 and 200 mg/L, respectively, which were about 3- and 2-fold as high as levels in cultures under similar conditions using Pharmamedia. For various amino acids tested, the addition of glutamic acid or aspartic acid mixture to the culture medium raised the apparent viscosity to its highest demonstrated value, 260 mPa.s after 5 d of culture, which was 3-fold higher than without amino acids. Consumption of the decomposed glutamic acid and aspartic acid was dependent on the activities of glutamate dehydrogenase and aspartate aminotransferase, respectively. When ammonium ion was used as the nitrogen source, cell concentration reached 1.75 g/L measured as an intracellular nucleic acid concentration, which was about 2.3-fold higher than that with any other natural nitrogen source. However, apparent viscosity was only 75 mPa.s, a value one-third that of the amino acid mixture, and 70% of the pellets were bigger than 1.2 x 10(4) microm(2). In the case of gluten meal or the amino acid mixture, pellets bigger than 1.2 x 10(4) microm(2) comprised only 8%. This demonstrates that consumption of some amino acids affected the formation of filamentous morphology, which caused an increase in the apparent viscosity of the culture broth, and the apparent viscosity was not caused by the mycelial concentration but the mycelial morphology.

Amino Acid Oxidoreductases↗
PubMedDate not supplied

Effect of viscosity upon hydrodynamically controlled natural aggregates of animal cells grown in stirred vessels.

The effect of medium viscosity upon cell growth and aggregate characteristics of baby hamster kidney (BHK) cells cultivated in stirred tanks was evaluated. Two thickening agents were tested, 9300 MW dextran and a low-viscosity sodium (carboxymethyl)-cellulose; both were used in two different sets of experiments: (i) 250 cm3 Wheaton spinner flasks with a ball impeller operated at 45 rpm; (ii) 500 cm3 Corning spinner flasks with a paddle impeller, operated at constant power dissipation (88 cm2 s-3). Aggregate diameter and the fraction of cells in aggregates increased with the increase in viscosity. Power laws were applied to the experimental results. A dependence of aggregate size upon power dissipation of the order of -0.19 and kinematic viscosity of 0.34 and 0.49 for the constant agitation and constant power dissipation tests were obtained, respectively. A model based upon the entire universal-equilibrium range (i.e., the entire spectrum of isotropic eddies) was used to predict theoretical relationships between the variables studied. The model leads to a power dependence of -0.25 for the energy dissipated in the entire universal-equilibrium range and between 0.25 and 0.5 for the kinematic viscosity in the viscous dissipation subrange, depending on the energy correlation used; it also gives a good explanation for the dependence of aggregate size on the hydrodynamics of the vessel.

Animals↗
PubMed2004

Analysis of genotypic and environmental effects on rice starch. 1. Apparent amylose content, pasting viscosity, and gel texture.

Eight rice varieties with wide diversity in apparent amylose content (AC) were selected and planted in the early season and late season of Hangzhou and in the winter season of Hainan for two consecutive years to study the genotype x environment effects on the starch properties of the grain. Analyses of variance showed that AC, cool paste viscosity, breakdown viscosity, setback viscosity, peak time, gel hardness, adhesiveness, and cohesiveness were mainly affected by genotypic variation, whereas peak viscosity and hot paste viscosity were mainly affected by environmental variation. The year x season, year x variety, seasonx variety, and year x season x variety effects were significant for most traits, indicating significant genotype x environment interactions. AC was significantly correlated with all other parameters except PV. Because the Wx gene controls the synthesis of amylose in rice, the mechanism of how the environment affects starch properties is discussed in relation to Wx expression and regulation. The implications of the results for rice breeders and starch-based food manufacturers are discussed.

Amylose↗
PubMed2000

Effects of solution polarity and viscosity on peptide deamidation.

Deamidation kinetics were measured for a model hexapeptide (L-Val-L-Tyr-L-Pro-L-Asn-Gly-L-Ala, 0.02 mg/mL) in aqueous solutions containing glycerol (0-50% w/w) and poly(vinyl pyrrolidone) (PVP, 0-20% w/w) at 37 degrees C and pH 10 to determine the effects of solution polarity and viscosity on reactivity. The observed pseudo-first order deamidation rate constants, k(obs), decreased markedly when the viscosity increased from 0.7 to 13 cp, but showed no significant change at viscosities >13 cp. Values of k(obs) also increased with increasing dielectric constant and decreasing refractive index. Molecular dynamics simulations indicated that the free energy associated with Asn side-chain motion is insensitive to changes in dielectric constant, suggesting that the observed dielectric constant dependence is instead related primarily to the height of the transition state energy barrier. An empirical model was proposed to describe the effects of the viscosity, refractive index and dielectric constant on k(obs). Analysis of the regression coefficients suggested that both permanent and induced dipoles of the medium affect the deamidation rate constant, but that solution viscosity is relatively unimportant in the range studied.

Amides↗
PubMed2002

Effect of viscosity on the deamidation rate of a model Asn-hexapeptide.

The effect of viscosity on the deamidation rate of a model Asn-containing hexapeptide (l-Val-l-Tyr-Pro-l-Asn-Gly-l-Ala) was assessed in aqueous solution and in solids containing varying amounts of poly(vinyl pyrrolidone) (PVP) and water. Stability studies were conducted at 0.1 mg/mL peptide and 0-50% PVP (w/w) in aqueous solution, and at 5% (w/w) peptide and different relative humidities (31.6, 53.1, 74.4 and 96%) in the solid state. The parent peptide and its deamidation products were analysed by reverse-phase high-performance liquid chromatography. Deamidation rates decreased with increasing solvent viscosity in a manner described by a semi-empirical mathematical model developed to describe this relationship. The results suggest that the motion of the Asn side-chain along the reaction coordinate is a function of the macroscopic solvent viscosity. However, the apparent energy barrier for the diffusive movement of the side-chain appears to be less than the energy barrier for that associated with macroscopic viscosity. The dependence of the deamidation rate on viscosity in both viscous solution and hydrated solids further demonstrates the importance of mobility in peptide deamidation.

Calorimetry, Differential Scanning↗
PubMed2001

Blood viscosity, hemodynamics and vascular hindrance in a rat model of acute controlled bleeding and volume restitution with blood or Haemaccel.

BACKGROUND: Hemorrhage and volume restitution with commercially available solutions is followed by reduced blood viscosity. Consequent hemodynamic changes may arise not only from the reduced viscosity itself but also from changes in vascular geometry induced by autoregulation processes. Vascular hindrance reflects the contribution of vascular geometry to flow. Our aim was to explore the possible effects of blood volume restitution with Haemaccel or blood, on regional blood flow and vascular geometry. METHODS: Under ketamine anesthesia, blood was withdrawn at a rate of 0.3 ml/min for 15 min followed by 15 min of stabilization. The shed blood or Haemaccel was infused at the same rate and volume as used for withdrawal. Hemodynamic measurements were performed using radioactive microspheres. Blood viscosity was measured with an Ostwald viscometer. Vascular hindrance was calculated as the resistance/viscosity ratio. RESULTS: Volume replacement with Haemaccel (n=10), compared to blood (n=10), was followed by increased cardiac output and portal venous inflow (37.1 +/- 9.0 and 3.1 +/- 0.5 vs 25.9 +/- 6.8 and 2.2 +/- 0.9 ml x min(-1) x 100 g bw(-1), respectively; P<0.05), decreased viscosity (2.8 +/- 1.3 vs 3.7 +/- 1.3, respectively; P<0.01) and decreased peripheral and splanchnic arteriolar resistance (3.8 +/- 1.1 and 40.9 +/- 7.6 vs 5.2 +/- 1.7 and 61.1 +/- 29.5 mmHg x ml(-1) x min x 100 g bw, respectively; P<0.05). No significant differences between the groups were observed in vascular hindrance and cardiac output distribution. CONCLUSION: Volume replacement with Haemaccel, compared to blood, induced increase in systemic and splanchnic blood flows, reflecting mainly changes in viscosity and not in blood vessel geometry. These results suggest no significant difference in overall activation of autoregulation process between volume restitution with blood or Haemaccel.

Animals↗
PubMed1994

Lack of dependence of cerebral blood flow on blood viscosity after blood exchange with a Newtonian O2 carrier.

Whether the increase in cerebral blood flow measured after hemodilution is mediated by a decrease in blood viscosity or in oxygen delivery to the brain is debated. In the present study, blood was replaced by an oxygen-carrying blood substitute, ultrapurified, polymerized, bovine hemoglobin (UPBHB). In contrast to normal blood, UPBHB yields a constant and defined viscosity in the brain circulation, since its viscosity is not dependent on the shear rate. CBF was determined after blood exchange with UPBHB in one group of conscious rats (UPBHB group) and in another group of blood-exchanged conscious rats in which viscosity was increased fourfold by the addition of 2% polyvinylpyrrolidone (PVP), mw 750,000 (UPBHB-PVP group). Local CBF (LCBF) was measured in 34 brain structures by means of the quantitative iodo(14C)antipyrine method. After blood replacement, systemic parameters such as cardiac index, arterial blood pressure, blood gases, and acid-base status were not different between the UPBHB and the UPBHB-PVP groups. In particular, arterial oxygen content was similar in both groups. Compared with a control group without blood exchange, LCBF was increased after blood exchange in the different brain structures by 60-102% (UPBHB group) and by 33-101% (UPBHB-PVP group). Mean CBF was increased by 77% in the UPBHB group and by 69% in the UPBHB-PVP group. No significant differences were observed in the values of LCBF or mean CBF between the UPBHB group and the UPBHB-PVP group. The results show that a fourfold variation in the viscosity of a Newtonian blood substitute does not result in differences in CBF values.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed2006

Systemically administered trefoil factors are secreted into the gastric lumen and increase the viscosity of gastric contents.

BACKGROUND AND PURPOSE: Trefoil factors (TFFs) secreted by mucus-producing cells are essential for the defence of the gastrointestinal mucosa. TFFs probably influence the viscoelastic properties of mucus, but this has not been demonstrated in vivo. We therefore studied the gastric secretion of systemically administered TFF2 and TFF3, and their influence on the viscosity of the secretions. EXPERIMENTAL APPROACH: Mice and rats under general anaesthesia were injected intravenously with human (h) TFF2, hTFF3 (5 mg kg(-1) to mice and 25 mg kg(-1) to rats), murine (m) (125)I-TFF3, or (125)I-hTFF3 (300,000 cpm, mice only). The appearance of TFFs in the gastric mucosa and luminal secretions was analysed by autoradiography, gamma-counting, and ELISA, and the viscosity by rheometry. KEY RESULTS: (125)I-mTFF3 and (125)I-hTFF3 were taken up by secretory cells of the gastrointestinal tract and detected at the gastric mucosal surface 15 min after injection. Stressing the stomach by carbachol (3.5 microg kg(-1)) and pyloric ligation significantly increased the uptake. Injected hTFF2, hTFF3, and mTFF3 were retrieved from the gastric contents after 4 h. In rats, an approximately seven-fold increase in the viscosity was detected after injection of TFF2 compared to the controls, whereas TFF3 did not increase the viscosity. In mice, TFF2 increased the viscosity approximately 4-fold. CONCLUSIONS: These data indicate that systemically administered TFFs are transferred to the gastric lumen in a biologically active form.

Animals↗
PubMed2003

Viscosity-dependent diastereoselectivity and product selectivity in the photodenitrogenation of a spirocyclopropane-substituted, DBH-type azoalkane.

In the photodenitrogenation of the spirocyclopropane-substituted azoalkane 1 in alcoholic solvents of various viscosity (from 0.6 to 89.2 cP) to the diastereomeric housanes 2 (major product) and bicyclo[3.2.0]heptenes 3 (minor product), the same (within experimental error) viscosity dependence is observed in the diastereoselectivity of the housane 2 formation as well as in the product selectivity (2/3). These viscosity effects corroborate the intermediacy of the diazenyl diradical 1DZ as a common branching point for the housane 2 and bicycloheptene 3 formation. In contrast, the diastereoselectivity of the bicycloheptene 3 generation is independent of viscosity, which implies that a nitrogen-free, symmetrical 1,4 diradical serves as precursor to the rearrangement products. The free-volume model of viscosity is employed to rationalize the product selectivity as well as the diastereoselectivity.

Alcohols↗
PubMed1982

Blood viscosity, glycaemic control and retinopathy in insulin-dependent diabetes.

1. In a cross-sectional study, 32 insulin-treated diabetic patients had elevated low shear (27.1 vs 22.1 mPa s, P less than 0.05) and high shear blood compared with 10 non-diabetic controls. After correction to 45% packed cell volume, the abnormality had a tendency to be greater in patients with proliferative (mean low shear viscosity, 30.8 mPa s) than background (29.2 mPa s) or nil/minimal retinopathy (27.6 mPa s, 0.05 less than P less than 0.97, permutational trend test). 2. The fibrinogen levels were higher in the diabetic group (P less than 0.05) and correlated with the low shear blood viscosity (rs = 0.38, P less than 0.05). 3. In a prospective study, 74 insulin-treated diabetic patients with background retinopathy were randomized into two groups. Thirty-six patients were on attempted improved therapy (A group); in these the mean glycosylated haemoglobin (Hb A1c) fell within 1 year (11.6 to 10.1%, P less than 0.001). both the corrected low shear blood and plasma viscosity fell similarly (P less than 0.001). The fall was greater than in those patients who were kept on usual therapy (U group) and whose glycosylated haemoglobin did not change significantly (11.7 to 11.4% over the year. 4. The effect of diabetes on blood viscosity may not be a direct pathological factor, as the same increased viscosity would be produced by a mean increase of 1.7% in packed cell volume, compared with a population range of 14% packed cell volume.

Adult↗
PubMed1998

Effects of hormone replacement therapies on fibrinogen and plasma viscosity in postmenopausal women.

In women, cardiovascular morbidity and mortality sharply increase after the onset of menopause. There is substantial evidence that hormone replacement therapy (HRT) may decrease the risk of coronary heart disease (CHD); however, the mechanisms of this preventive effect are unclear. We investigated the association between HRT and plasma viscosity as well as fibrinogen levels in postmenopausal women of a population-based sample (n=300, age 52-65 years). A total of 94 women used HRT; of these, 50 took oestrogen monotherapy and 44 used oestrogen-progesterone combinations. HRT was associated with significantly lower fibrinogen concentrations (2.32 v 2.68 g/l, P<0.001) and decreased plasma viscosity (1.147 v 1.176 mPa/s, P=0.01). Multivariate analyses controlling simultaneously for the effects of age, smoking, body mass index, and use of diuretics confirmed decreased fibrinogen and plasma viscosity values in women using HRT. A trend towards lower plasma viscosity (1.139 v 1.160 mPa/s) and plasma fibrinogen (2.28 v 2.44 g/l) was observed in women on oestrogen-progesterone combinations as compared with oestrogen monotherapy users: however, after controlling for the above-mentioned variables these differences were not statistically significant. This study demonstrates decreased plasma viscosity in women on HRT. Improved rheology offers a mechanism by which HRT lowers the risk of CHD in postmenopausal women.

Aged↗