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At least 325 records · Page 18Linked to original sources
PubMed2001

Interaction of the antimicrobial peptide gramicidin S with dimyristoyl--phosphatidylcholine bilayer membranes: a densitometry and sound velocimetry study.

We determined changes in the volume and adiabatic compressibility of large multi- and unilamellar vesicles composed of dimyristoylphosphatidylcholine containing various concentrations of the antimicrobial peptide gramicidin S (GS) by applying densitometry and sound velocimetry. Gramicidin S incorporation was found to progressively decrease the phase transition temperature of DMPC vesicles as well as to decrease the degree of cooperativity of the main phase transition and to increase the volume compressibility of the vesicles. GS probably enhanced thermal fluctuations at the region of main phase transition and provide more freedom of rotational movement for the phospholipid hydrocarbon chains. The ability of GS to increase the membrane compressibility and to decrease the phase transition temperature is evidence for regions of distorted membrane structure around incorporated gramicidin S molecules. At relatively high GS concentration (10 mol%), more significant changes of specific volume and compressibility appear. This might suggest changes in the integrity of the lipid bilayer upon interaction with high concentrations of GS.

Anti-Bacterial Agents↗
PubMed1978

Determination of individual hydroxyethyl rutosides in various animal body fluids by thin-layer chromatography and scanning densitometry.

A method is described for the accurate determination in plasma of the beta-hydroxyethylrutosides by measurement of the fluorescence of their borocitrate complexes by scanning densitometry following separation by thin-layer chromatography. A modification is also described for estimation of individual hydroxyethylrutosides and their glucuronide conjugates in samples of bile and urine.

Animals↗
PubMed1975

[Quantitative determinaton of glycerides by densitometry (author's transl)].

After determination of charring conditions and the measurement by densitometry of lipids separated by thin-layer chromatography, a statistical analysis was performed to determine the significance of the results. Calibration curves were studied and response factors calculated for some saturated and unsaturated triglycerides.

Chromatography, Thin Layer↗
PubMed1990

Quantitation of hexadecylphosphocholine by high-performance thin-layer chromatography with densitometry.

A method for the determination of the antineoplastic ether phospholipid hexadecylphosphocholine (HePC) is presented, based on the separation of the lipids by high-performance thin-layer chromatography charring with a cupric sulphate reagent and quantitation by in situ densitometry. The lower limit of determination is ca. 25 pmol. Concentrated hexane-isopropanol extracts of plasma samples can be applied to the plate without further clean-up, making this method useful for clinical drug monitoring. Additional ion-exchange chromatography and removal of the salt contaminants by gel filtration permits the study of endogenous phospholipids together with HePC from the same sample.

Choline↗
PubMed1984

A quantitative densitometric method for the rapid separation and quantitation of the major tissue and lipoprotein lipids by high-performance thin-layer chromatography. I. Sample preparation, chromatography, and densitometry.

A rapid method for the separation and quantitation of the major lipids of tissues and lipoproteins by automated high-performance thin-layer chromatography is presented. Solvent systems for one-dimensional separation of neutral lipids, of cholesteryl esters, and of phospholipids are described. Separated lipids are measured following treatment with methanolic sulphuric acid containing manganese chloride and scanned in fluorescence or absorption mode. Absolute quantitation is obtained by the use of an internal standard and by references to standards for each lipid run on the same plates as samples. The method described here is particularly suitable for the rapid quantitation of small amounts of lipid (0.01-0.02 nmol per sample), for example in tissue culture studies; 100 micrograms of fibroblast or macrophage protein are sufficient for complete lipid analysis. The coefficients of variation due to the sample preparation, application to the plates and densitometry are in the range 7.2-9.1%. The method was compared with enzymatic determinations for cholesterol and gave correlation coefficients of 0.95 for total cholesterol and 0.91 for unesterified cholesterol. Phospholipid estimation was compared with large-plate thin-layer chromatography and phosphorus analysis and gave correlation coefficients of 0.90 for phosphatidylcholine and 0.89 for sphingomyelin.

Animals↗
PubMed1989

Progress in densitometry for quantitation in planar chromatography.

The principal methods for obtaining quantitative information from separations performed by planar chromatographic techniques are reviewed. Recent advances in obtaining structural information for sample identification of separated components are also discussed. Reasonable expectations concerning future developments in densitometry are made.

Chemistry, Clinical↗
PubMed1997

Concurrent quantification of cellular cholesterol, cholesteryl esters and triglycerides in small biological samples. Reevaluation of thin layer chromatography using laser densitometry.

Absolute specificity and high accuracy is required for the quantitation of cholesterol, cholesteryl esters and triglycerides in small biological samples, particularly in a limited number of cells. Both can be achieved through thin-layer chromatography and molybdatophosphoric acid staining, while the shortcomings of traditional spot detection are overcome by laser densitometry. The major advantage of the proposed technique is the concurrent assay of nanogram quantities of cholesterol, cholesteryl esters and triglycerides. Our assay is at least ten-fold more sensitive than common thin-layer chromatography-based techniques and at least four-fold more sensitive than common enzymatic methods. The present low-cost assay is highly reproducible and may be particularly suitable for the routine lipid analysis of a 10% aliquot of relatively small tissue and cell samples, equivalent, for instance, to > or = 10(4) human monocytes.

Cholesterol↗
PubMed1997

Bile acid kinetics in man studied by radio thin-layer chromatography and densitometry coupling.

A method based on coupling of the techniques of radioscanning a TLC plate and densitometry has been developed for the determination of pool sizes and fractional turnover rate of bile acids in man after intraduodenal administration of 14C-labelled acid. The validity of the method has been checked by comparison of the results obtained with those of an enzymatic spectrophotometric analysis, and a measurement of the radioactivity by liquid scintillation counting, after elution of the separated bile acid from a TLC plate. Advantages of the proposed method over the previous one include a reduced number of manipulations, the possibility of automation, a better reproducibility, and the possibility of elaborating the radiometric data obtained for the primary bile acid for better characterising its metabolism inside the enterohepatic circulation.

Carbon Radioisotopes↗
PubMed1997

Analysis of aporphine and quinolizidine alkaloids from Caulophyllum thalictroides by densitometry and HPLC.

High-performance liquid chromatographic (HPLC) and densitometry procedures were developed to determine the principal alkaloids in the roots of C. thalictroides. In both techniques the alkaloids content was assessed using cytisine as an internal standard. The purity and identity of the peaks of the alkaloids was examined by diode array detection and by comparison with the standards. The content of individual alkaloids was found to be in the range 0.02-1.1% w/w.

Alkaloids↗
PubMed1997

Determination of glafenine in dosage forms and serum by thin layer densitometry and high performance liquid chromatography.

New thin layer densitometry and high performance liquid chromatography (HPLC) methods are described for quantitative determination of glafenine in dosage forms in the presence of its photo-degradation products and in serum in the presence of its metabolites. Mobile phases consisting of toluene-isopropyl alcohol-dimethylformamide-water (18:3:1:0.5) and methanol-water-phosphoric acid (80:120:0.5) are found to be efficient for reasonable separation and adequate resolution of glafenine from associated substances by thin layer chromatography (TLC) and HPLC techniques, respectively. The methods are used for the study of glafenine purity, stability, bioavailability, bioequivalence and tablet dissolution rate. The results obtained by TLC and HPLC techniques are in good agreement and offer the advantages of reproducibility and accuracy.

Analgesics, Non-Narcotic↗
PubMed1997

Comparison of integrated backscatter values obtained with acoustic densitometry with values derived from spectral analysis of digitized signals from a clinical imaging system.

Time-domain-based integrated backscatter values obtained with the use of acoustic densitometry (AD) were compared with values determined from a spectral-based analysis of the radio-frequency (RF) signals with a modified Hewlett-Packard Sonos 1500 imaging system. Integrated backscatter images of five specimens of bovine tendon were acquired in the AD acquisition mode, and the corresponding signals related to the backscattered RF were digitized for each angle of insonification as the specimens were rotated in 10-degree increments. The integrated backscatter images were analyzed with the AD analysis package, and the corresponding values determined from the RF power spectra were obtained from the digitized ultrasonic signals. Good agreement was found between the two methods over the entire range of measured values. The mean anisotropy in the measured integrated backscatter (mean +/- standard error) was found to be 27 +/- 2 dB for time-domain-based analysis and 25 +/- 2 dB for RF spectral-based analysis.

Acoustics↗
PubMedDate not supplied

Changes in body fat: measurements by neutron activation, densitometry and dual energy X-ray absorptiometry.

The measurement of body fat in ten subjects (BMI from 22 to 43 kg/m2), and in particular the changes arising from a ketogenic diet, by the techniques of in vivo neutron activation analysis (NAA), densitometry (using two- and four-compartment models) by under water weighing (UWW) and dual energy X-ray absorptiometry (DXA) was compared. The association between techniques for the fat changes was generally high (r = 0.70 to 0.98) and significant (p < 0.05). Assessment of agreement between DXA and the other techniques revealed discrepancies with significant slope and high association (r = -0.81 and -0.64). Whilst NAA and UWW appeared to measure similar changes, DXA underestimated small changes.

Absorptiometry, Photon↗
PubMed2003

Ultrasonographic densitometry of the lungs at autopsy: a preliminary investigation for possible application in forensic pathology.

The aim of the present study was to examine the possible application of ultrasonographic (US) densitometry of the lungs to quantitative evaluation of pulmonary edema at autopsy (n=85). A diagnostic ultrasound device LOGIQ alpha200 (GE Yokogawa Medical Systems) equipped with an LH probe (linear, 7.5 MHz) was used and each lobe of the lungs was scanned on the anterior and posterior surfaces after resection. The US density showed a correlation between the left and right lobes, and also between the anterior and posterior surface scans of each lobe. Although there was a correlation between the US density and combined lung weight in total cases, the density ranged very widely when lung weight was below about 1300 g, depending on the cause of death. The density was high in drowning, asphyxia, poisoning and delayed traumatic death, whereas it was usually low in fire death mainly due to burns, hemorrhagic shock and head injury. In the other causes of death, a considerable case-to-case difference was observed independent of the lung weight. These findings suggested a possible contribution of pulmonary edema to high US density, possibly depending on the survival time and irrespective of the blood contents (congestion or postmortem hypostasis).

Adolescent↗
PubMed2004

Pulse dye densitometry using indigo carmine is useful for cardiac output measurement, but not for circulating blood volume measurement.

BACKGROUND AND OBJECTIVE: We evaluated the validity of a newly developed pulse dye densitometer for indigo carmine for measuring cardiac output and circulating blood volume. METHODS: Measurements of cardiac output and circulating blood volume were performed with the indigo carmine densitometer during normovolaemia, hypovolaemia and hypervolaemia in nine mongrel dogs under general anaesthesia. The validity was evaluated by comparison of the values of cardiac output and circulating blood volume obtained by the thermodilution technique and the 51Cr-labelled red blood cell method, respectively. We also examined indigo carmine removal by continuous veno-venous haemofiltration after indigo carmine injection. RESULTS: There was good agreement between dye densitometer- and thermodilution-derived cardiac output (r = 0.885, P < 0.001). The bias and limits of agreement of these values were 0.09 and+/-1.07 L min(-1) (2 SD, n 22), respectively. The dye-densitometer-derived circulating blood volume was greater than that of the 51Cr-labelled red blood cell method, and both values showed weak agreement (r = 0.587, P < 0.027). The sieving coefficient of indigo carmine through continuous veno-venous haemofiltration was 0.34+/-0.06. CONCLUSIONS: These data indicate that indigo carmine densitometry is a reliable method for cardiac output determination, but it overestimates circulating blood volume, probably due to the transition of indigo carmine into the extravascular space in the systemic circulation.

Algorithms↗
PubMed2002

Determination of saponins in legumes by direct densitometry.

Research has shown that dietary saponins may have health benefits. A simple, rapid method for the determination of saponins in legumes, using densitometry, is described. Saponin preparations, after pretreatment to remove nonsaponin components, are spotted in rows on a thin-layer chromatography plate, along with soyasaponin standards. The plate, without solvent development, is directly treated with sulfuric acid and heated. Violet spots develop which have a density proportional to the amount of saponin present. The standard curve has a correlation coefficient of 0.99 and is linear over the range of 1.25 to 10 microg of soyasaponins applied. The method has a coefficient of variation of less than 3% and compares favorably with quantitative thin-layer chromatography. Using this method the saponin contents of defatted soy flour (0.58%), dried navy beans (0.32%), and dried kidney beans (0.29%) were determined, and these results were found to be consistent with previous reports in the literature.

Chromatography, Thin Layer↗
PubMed1998

Measurement of blood concentration of indocyanine green by pulse dye densitometry--comparison with the conventional spectrophotometric method.

OBJECTIVE: Pulse dye densitometry (PDD) uses two wavelengths (805 and 890 nm) in association with pulse oximetry to compute the arterial blood concentration ratio of indocyanine green (ICG) to hemoglobin (Hb). When Hb is measured in the usual way, this permits the PDD to compute cardiac output, plasma or blood volume, and liver blood flow following an intravenous injection of ICG. In this study, we evaluate the accuracy of the PDD calculation of dye concentration by comparing it with measurement of the dye concentration in blood (Cb) measured by the spectrophotometric cuvette method during dye clearance in patients. METHODS: In 25 patients receiving major abdominal surgery, ICG (10, 20, or 40 mg) was injected into a central vein and arterial ICG concentration was continuously and simultaneously monitored at nose and finger by PDD; concurrently, ICG concentrations were measured by a spectrophotometer at 805 nm in 4 radial arterial blood samples. Repeated measures or one-way ANOVA were used for comparison of ICG concentrations and percent errors by PDD at the nose, finger, and Cb. RESULTS: The percent error (bias) of calculated dye concentration and its standard deviation (precision) was -3.9 +/- 16.8% (p < 0.01) with the probe on a nostril and 3.4 +/- 12.6% using the finger probe. These errors were found to be greatest when the mean transit time of the dye was rapid (-20.7 +/- 6.8% at nose p < 0.01 and -8.5 +/- 2.5% at finger p < 0.05) due to factors other than the time delay of blood sampling. CONCLUSION: These errors are of similar size to those associated with thermal cardiac output measurement, suggesting that PDD should be valuable clinically as a noninvasive tool especially since it provides values for blood volume and liver blood flow.

Aged↗
PubMed1996

Ultrasound bone densitometry and dual energy X-ray absorptiometry in patients with spinal cord injury: a cross-sectional study.

Bone is lost following spinal cord injury (SCI) and in the long-term may become osteopenic and liable to fracture. Two non-invasive techniques, ultrasound bone densitometry (USBD) and dual energy X-ray absorptiometry (DXA), have been applied to monitor bone changes after spinal injury. 31 SCI patients were scanned using an ultrasound bone densitometer, to give measurements of speed of sound (SOS), broadband ultrasound attenuation (BUA) and "stiffness'. The time since injury of these patients ranged between 5 weeks to 36 years with a mean of 5.87 +/- 10.21 years. Ultrasonic properties at the calcaneus of these patients were significantly lower than the healthy reference population, and a rapid decline in ultrasound properties occurred in the first 3 months. The fall continued up to 54 months but at a slower rate. The normal linear relationship between SOS and BUA was not altered by SCI. Eighteen patients had DXA measurements at the lumbar spine and the right proximal femur. Bone mineral density (BMD) at the femoral neck was significantly lower than the normal reference population (P < 0.05). SOS and "stiffness' correlated significantly with BMD at the lumbar spine, Ward's triangle, the femoral neck, the greater trochanter and the intertrochanteric site (P < 0.05). BUA correlated significantly at all these sites with the exception of the trochanter. A negative correlation was found between the ultrasonic properties at the calcaneus and BMD at the lumbar spine which is in contrast to the positive relationship in normal subjects. There was a tendency for BMD to increase at the lumbar spine after the first 12 months after injury, although this trend was not significant overall. The "stiffness' at the calcaneus and BMD at the femoral neck were lower than the reference population following 12 months since injury. These results show that bone deficit at the calcaneus occurs rapidly and to a severe degree after SCI, and that ultrasound has an important role to play in the assessment of bone status in these patients.

Absorptiometry, Photon↗
PubMed2002

Differences in distribution of T-scores and Z-scores among bone densitometry tests in postmenopausal women (a comparative study).

BACKGROUND: To determine the character of T-score and Z-score value distribution in individually selected methods of bone densitometry and to compare them using statistical analysis. METHODS: We examined 56 postmenopausal women with an age between 43 and 68 years with osteopenia or osteoporosis according to the WHO classification. The following measurements were made in each patient: T-score and Z-score for: 1) Stiffness index (S) of the left heel bone, USM (index). 2) Bone mineral density of the left heel bone (BMDh), DEXA (g of Ca hydroxyapatite per cm2). 3) Bone mineral density of trabecular bone of the L1 vertebra (BMDL1), QCT (mg of Ca hydroxyapatite per cm3). The densitometers used in the study were: Ultrasonometer to measure heel bone, Achilles plus LUNAR, USA; DEXA to measure heel bone, PIXI, LUNAR, USA; QCT to measure the L1 vertebra, CT, SOMATOM Plus, Siemens, Germany. STATISTICAL ANALYSIS: Differences between measured values of T-scores (Z-scores) were evaluated by parametric or non-parametric methods of determining the 95% confidence intervals (C.I.) RESULTS: Differences between Z-score and T-score values for compared measurements were statistically significant; however, these differences were lower for Z-scores. CONCLUSIONS: Largest differences in 95% C.I., characterizing individual measurements of T-score values (in comparison with Z-scores), were found for those densitometers whose age range of the reference groups of young adults differed the most, and conversely, the smallest differences in T-score values were found when the differences between the age ranges of reference groups were smallest. The higher variation in T-score values in comparison to Z-scores is also caused by a non-standard selection of the reference groups of young adults for the QCT, PIXI and Achilles Plus densitometers used in the study. Age characteristics of the reference group for T-scores should be standardized for all types of densitometers.

Adult↗