Search results for "CHROMATOGRAPHY"
showing 10 items of 5037 documents
Micellar liquid chromatography for prediction of drug transport.
2000
Abstract The vast majority of well absorbed drugs are transported passively across the cell membranes. Physicochemical descriptors of drug molecules that are believed to influence transcellular transport are routinely used to predict drug absorption by means of complex mathematical models. In this paper, a new in vitro method, based on the retention data in micellar liquid chromatography (MLC), is validated for the prediction of passive drug absorption. The retention of a heterogeneous drugs set in MLC using Brij 35 as surfactant in the mobile phase is compared with the retention data reported in literature obtained in red cell membrane lipid liposomes, human red cell membranes vesicles (ve…
Influence of gamma-aminobutyric acid on baclofen intestinal absorption.
1994
Since previous studies suggested that baclofen absorption in the rat middle intestine was inhibited by beta-alanine and therefore mediated, at least in part, by the beta-aminoacid carrier, we focused our new studies on the analysis of the possible inhibition of the drug by a gamma-aminoacid model compound, gamma-aminobutyric acid (GABA). A rat jejunum in situ study was undertaken in order to evaluate the effect of GABA on baclofen absorption and to establish the inhibition model. Assays using isotonic perfusion solutions of 0.5 mM baclofen with starting GABA concentrations ranging from 0 to 100 mM are reported. The results show that the absorption rate pseudoconstants of the drug decrease a…
Partially competitive inhibition of intestinal baclofen absorption by beta-alanine, a nonessential dietary aminoacid.
1991
In situ intestinal absorption of baclofen in the rat in the presence of beta-alanine has been investigated. Through the perfusion of 0.50 mM baclofen solutions containing variable concentrations of the aminoacid (from 5 to 100 mM), a partially competitive inhibition of baclofen absorption was characterized: absorption rate pseudoconstants of the spasmolytic drug decrease as beta-alanine concentration increases, until a limiting value is obtained (36.8 per cent of that found for baclofen alone). A computer method was developed in order to calculate parameters governing baclofen absorption in the presence of beta-aminoacid, with the following results: Vm = 11.22 mM h-1; Km = 7.42 mM; Ki = 2.4…
Intestinal absorption pathway of gamma-aminobutyric acid in rat small intestine.
1994
Intestinal absorption of gamma-aminobutyric acid (GABA), as a model compound for gamma-aminoacids, has not been extensively studied from the kinetic viewpoint. Since data from our laboratory suggested that some competition arises between intestinal absorption of beta-alanine and GABA and since our intent was to maintain the aqueous stagnant diffusion layer in order to approach absorption tests to in vivo physiological conditions, a rat jejunum in situ study was undertaken in order to gain an insight into the mechanism of GABA absorption. In the present paper, results from assays using isotonic perfusion solutions with starting GABA concentrations ranging from 1 to 50 mM are reported. They s…
Quantitative analysis of the effect of controlled-release formulation on nonlinear gastrointestinal absorption of P-glycoprotein substrate talinolol …
2020
Abstract Oral absorption of talinolol, a substrate of P-glycoprotein (P-gp), from a sustained-release (SR) formulation was reportedly decreased compared to that from an immediate-release (IR) formulation. The aim of this study was to predict and understand the effect of controlled-release formulation on the oral absorption of P-gp substrates by developing a physiologically based pharmacokinetic (PBPK) absorption model incorporating multiple kinetic parameters obtained from in vitro studies, using talinolol as a model substrate. Simulation analysis using the developed PBPK absorption model indicated that the clinically observed marked decrease in the plasma concentration of talinolol adminis…
Effect of simulated gastrointestinal digestion on plant sterols and their oxides in enriched beverages
2013
Abstract This study evaluates the bioaccessibility (percentage of soluble compound available for absorption) of plant sterols (PS) and their oxides (phytosterol oxidation products, POPs) after simulated gastrointestinal digestion in fruit (Fb), milk (M) and fruit-based milk beverages with (FbM a ) or without (FbM b ) tangerine juice. In beverages and their bioaccessible fraction (BF), campesterol, campestanol, stigmasterol, β-sitosterol and sitostanol were detected. Bioaccessibility of total PS ranged between 2.62 and 6.48%, FbM b yielding the highest value, followed by FbM a > Fb > M. Campesterol/campestanol were the most bioaccessible PS. Only oxides of β-sitosterol were detected in beve…
Effect of cooking on oxalate content of pulses using an enzymatic procedure.
2003
An enzymatic method proposed for the determination of oxalate in urine is adapted for the estimation of soluble oxalate content in beans, chickpeas and lentils. Oxalates were extracted in water by refluxing for 2 h. The method is based on the oxidation of oxalate by the oxidase and the determination of the resulting hydrogen peroxide, which in presence of peroxidase, 3-methyl-2 benzotiazinolone and 3-dimethylamino benzoic, gives an indamine compound with an absorption maximum at 590 nm. The linearity (from 0.015 to 0.6 mM) of the method is adequate to the analysis of oxalate contents in pulses, and the inter-day precision of the method expressed as relative standard deviation was good (3.01…
Physiologische Wirkungen und Stoffwechsel dimerer Fettsäuren
1964
Die langfristige Verfutterung von 5% dimeren Fettsauren entspr. rund 1,5 g/kg Korpergewicht (bezogen auf das Endgewicht) ergab toxische Wirkungen: Wachstumsverzogerungen, verschlechterte Futterefficiency, Verschlechterung des Grundumsatzes, Senkung der Korpertemperatur, Storung der Leberfunktion und Ablagerung eines abnormen Pigments im RES und in Organzellen.
A comparative study on sample preparation procedures for supplementary foods by ICP-OES: Green chemistry considerations
2015
An inductively coupled plasma optical emission (ICP-OES) method was developed for the simultaneous determination of major, minor and trace elements in food. Preliminary studies focused on selecting suitable operational conditions in order to provide the highest sensitivity and to maximize the number of analytes to be determined without spectral or matrix interference. Ruthenium and rhenium were evaluated as internal standards and samples were analyzed at different dilution levels. Furthermore, a comparative study was carried out by using three sample digestion methods, microwave-assisted digestion with HNO3/H2O2, dry ashing and dry ashing with Mg(NO3)2/MgO as an ashing aid. Adequate precisi…
Fluorimetric determination of amphetamine in urine by flow injection with on-line liquid–liquid extraction
2001
Abstract Determination of amphetamine in urine was performed by batch and flow injection methodologies. The suitable experimental conditions for fluorimetric measurements were established. The liquid–liquid extraction was carried out at pH 13 using diethyl ether as extracting reagent. The measurement conditions were 260 nm and 277 nm for excitation and emission wavelengths, respectively. The method requires standard addition calibration and Youden blank correction. The influence of the main metabolites of amphetamine and metamphetamine were studied. The accuracy and precision of the proposed method was tested and the method is adapted to the flow injection procedure with on-line extraction.