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At least 1,207 records · Page 67Linked to original sources
PubMed2001

Determination of inorganic acids by ion chromatography with n-tetradecylphosphocholine (zwitterionic surfactant) as the stationary phase and pure water as the mobile phase.

A new ion chromatographic (IC) system, in which n-tetradecylphosphocholine (TDPC, a phosphobetaine type of zwitterionic surfactant) was used as the stationary phase, pure water as the mobile phase, and conductivity as the method of detection, has been developed for the determination of inorganic acids. Five model acids, HCl, HNO3, HClO4, H2SO4, and H3PO4, were separated to baseline and eluted in the order H3PO4 > HCl > HNO3 > H2SO4 > HClO4. When peak areas were plotted against the concentrations of the acids in samples, linear calibration curves were obtained. Ultimate determination limits were approximately 1 mmol L(-1), but the discrimination of the method between solutions of different concentration was better than 10 micromol L(-1) for those model analytes. Salts of divalent cations could also be separated, but they were eluted faster than the acids. No separation was observed for the salts of monovalent cations. This newly proposed approach is applicable to the simultaneous determination of the inorganic acids (produced by reactions of NOx, SOx, and HCl with water) in aerosols.

Acids↗
PubMed2005

Change in palatoglossus muscle activity in relation to swallowing volume during the transition from the oral phase to the pharyngeal phase.

The purpose of this study was to examine whether the palatoglossus (PG) muscle is involved in the regulation of function during the transition from the oral to the pharyngeal phase. Seven normal adults participated in the study. Smoothed electromyography (EMG) signals of the PG muscle and levator veli palatini (LVP) muscle were collected. Each subject swallowed water at five different volumes: 12.5%, 25%, 50%, 100%, and 150% (or 200%) of his/her optimum swallowing volume. PG muscle waveform showed two patterns of activity: one of a single peak and the other of two peaks. There was no significant difference (p < 0.01) in the timing of emergence between the single peak and the second peak of the two-peak pattern. There were two patterns of PG muscle activity in response to a change in swallowing volume, i.e., one was a pattern in which the activity was correlated to the change in swallowing volume, the other was a pattern in which the activity was not changed but almost at the maximum activity level, irrespective of swallowing volume. We conclude that the PG muscle could be involved in the regulation of swallowing from the oral to the pharyngeal phase. The activity could be influenced by swallowing volume.

Adult↗
PubMed2006

Change in levator veli palatini muscle activity in relation to swallowing volume during the transition from the oral phase to pharyngeal phase.

The aim of this study was to examine whether the levator veli palatini (LVP) muscle might be involved in the regulation of velopharyngeal function during the transition between the oral and pharyngeal phases during swallowing, and to examine whether LVP muscle activity could be regulated in relation to the volume of swallowing. Eight normal adults participated in this study. Smoothed EMG signals of the LVP muscle were collected. At the same time, palatoglossus muscle activity was also monitored. Each subject swallowed water at five different volumes: 12.5%, 25%, 50%, 100%, and 150 (or 200) % of the optimum volume for swallowing, which was individually determined for each subject. LVP muscle activity was positively correlated with changes in swallowing volume. The LVP muscle was involved in the regulation of swallowing during the transition from the oral to pharyngeal phases.

Adult↗
PubMed2006

Predictions of the in vivo clearance of drugs from rate of loss using human liver microsomes for phase I and phase II biotransformations.

PURPOSE: The utility of in vitro metabolism to accurately predict the clearance of hepatically metabolized drugs was evaluated. Three major goals were: (1) to optimize substrate concentration for the accurate prediction of clearance by comparing to Km value, (2) to prove that clearance of drugs by both oxidation and glucuronidation may be predicted by this method, and (3) to determine the effects of nonspecific microsomal binding and plasma protein binding. METHODS: The apparent Km values for five compounds along with scaled intrinsic clearances and predicted hepatic clearances for eight compounds were determined using a substrate loss method. Nonspecific binding to both plasma and microsomal matrices were also examined in the clearance calculations. RESULTS: The Km values were well within the 2-fold variability expected for between laboratory comparisons. Using both phase I and/or phase II glucuronidation incubation conditions, the predictions of in vivo clearance using the substrate loss method were shown to correlate with published human clearance values. Of particular interest, for highly bound drugs (>95% plasma protein bound), the addition of a plasma protein binding term increased the accuracy of the prediction of in vivo clearance. CONCLUSIONS: The substrate loss method may be used to accurately predict hepatic clearance of drugs.

Algorithms↗
PubMed1992

Automated analysis of the pyridinium crosslinks of collagen in tissue and urine using solid-phase extraction and reversed-phase high-performance liquid chromatography.

A fully automated method for assaying the collagen crosslinking amino acids, pyridinoline and deoxypyridinoline, in human urine samples or tissue hydrolysates is described. Samples were processed using a Gilson ASPEC system with solid-phase extraction of the crosslinks on columns containing 100 mg of microgranular cellulose. Introduction of an additional solvent step during sample preparation allowed direct analysis by reversed-phase HPLC and elimination of the drying step used previously in a manual method. Use of a synthetic pyridinoline derivative as internal standard enabled accurate quantification of the crosslinks by correcting for recoveries through the whole assay. Samples were analyzed in sequential mode with a total assay time of 30 min. The automated assay showed close correlation with the manual method for both free and total crosslink determinations in human urine (r > 0.97). Reproducibility was improved, as seen from replicate analyses of human urine (CV < 3% for automated pyridinoline measurement compared with 8-12% previously observed for the manual method). Crosslink excretion is the most useful marker of collagen degradation in metabolic bone diseases and arthritic disorders. The automated assay which has been developed is rapid, convenient, and reliable and will greatly facilitate the monitoring of urinary collagen crosslinks and their tissue levels in clinical investigations.

Amino Acids↗
PubMed1982

Optical detection of phase transitions in simple and mixed lipid-water phases.

A simple method for the detection of phase transitions in lipid-water systems by recording the intensity of the transmitted light through a sample placed between crossed polarizers as a function of the temperature was developed. A very small amount of lipid material is sufficient for its effective application. Two zwitterionic lipids in water, dipalmitoylphosphatidylcholine (DPPC) and dipalmitoylphosphatidylethanolamine (DPPE) as well as their mixtures were studied by means of this method. The results were compared with differential scanning calorimetry (DSC) data and a good correspondence was established. A phase diagram of the DPPC-DPPE mixture is constructed. This study also throws additional light on the nature of the 'pretransition' of DPPC.

Birefringence↗
PubMed1983

The influence of water on the phase transition of sheep lung surfactant. A possible mechanism for surfactant phase transitions in vivo.

The effect of water on the thermal properties of sheep lung surfactant lipids was determined by differential scanning calorimetry. Dry surfactant exhibited a phase transition with an upper limit of about 54 degrees C, whereas that of the fully hydrated surfactant was about 30 degrees C. The effect of water was confined to a range of hydration values from 0 to 25%. The results indicate that pulmonary surfactant lipids are capable of undergoing both thermotropic and lyotropic mesomorphism in vitro. The degree of hydration of the surfactant could influence its in vivo biophysical role in alveolar dynamics. Indeed, small changes in the surfactant to water ratio induced by regional differences in the surfactant concentration at the alveolar surface during alveolar expansion and contraction could be sufficient to trigger isothermal phase transitions in the surfactant lipids. This would allow changes to occur in the equilibrium between solidus and fluidus surfactant during the respiratory cycle.

Animals↗
PubMed1995

Phases and phase transitions of the sphingolipids.

LIPIDAT is a computerized database providing access to the wealth of information scattered throughout the literature concerning synthetic and biologically derived polar lipid polymorphic and mesomorphic phase behavior. Herein, we present a review of the LIPIDAT data subset referring to sphingolipids together with an analysis of these data. It includes data collected over a 40-year period and consists of 867 records obtained from 112 articles in 25 different journals. An analysis of these data has allowed us to identify trends in hydrated sphingolipid phase behavior reflecting differences in fatty acyl chain length, saturation and hydroxylation, head group type, and sphingoid base identity. Information on the mesomorphism of biologically-derived and dry sphingolipids is also presented. This review includes 161 references.

Animals↗
PubMed1996

Phase transitions of rat stratum corneum lipids by an electron paramagnetic resonance study and relationship of phase states to drug penetration.

In order to relate barrier function to stratum corneum structure and the thermal transitions of corneum lipids, samples from hairless rat skin were investigated by using ESR and drug penetration techniques. The phase transition of stratum corneum lipids was estimated using a deeper probe (16-doxyl-stearic acid) inserted in the lipid bilayers and measuring the rotational correlation time, tau(c). Results of ESR study showed that stratum corneum lipids underwent thermal transitions at 39.3 +/- 1.6 degrees C and 63.6 +/- 2.6 degrees C roughly similar to the data obtained by differential scanning calorimetry measurements. Cholesterol oxidase treatment decreased the fluidity of the lipids at lower temperatures. The treatment of stratum corneum with laurocapram (1%) and isopropyl myristate (IPM, 2%) little changed both phase transition temperatures, although the treatment highly increased the molecular motion of the lipids. The flux (J(s)) of lipophilic drugs (beta-estradiol, indomethacin and betahistine) through the skin was enhanced with increasing temperatures, with an increase in the diffusion constant within skin and a decrease in the lag time. There was a good relationship between log J(s) or log permeability coefficient (K(p)) and 1/tau(c) in the temperature range of 45 to 64 degrees C. The calculated activation energy (delta E) for diffusion of these drugs across skin was 17-40 kcal/mol. Judging from our data, stratum corneum lipids of rat probably exist as the gel, crystalline state below 39 degrees C, the mesomorphic state between 39 and 64 degrees C and the fluid, liquid-crystalline state at temperatures of 64 degrees C or above. These results are in line with the permeability of these lipophilic drugs through the intercellular lipids disordered is highly increased.

Animals↗
PubMed1990

Superoxide anion radical induces lipid phase transitions that mimic temperature-induced phase-transition phenomenon of membrane lipids.

A biological membrane is shown to undergo lipid-phase transition leading to increased membrane fluidity when exposed to extraneously generated superoxide anion radical. This phase-transition is several folds higher in magnitude when compared to the temperature-induced fluidity change at the transition temperatures. This finding could have significant importance since an altered membrane configuration may involve aspects of biochemistry, biophysics or physiology.

Animals↗
PubMed1989

Sex hormone-mediated effects on the phase I and phase II metabolism of N-2-fluorenylacetamide. Modulation of 9-hydroxylation.

Sex differences in the phase I (cytochrome P-450-catalyzed hydroxylations) and phase II (conjugations) metabolism of N-2-fluorenylacetamide (2-FAA) by the livers of 50-day-old Sprague-Dawley rats and effects of gonadectomy were determined. The higher level (1.4 times) of cytochrome P-450 in the microsomes of male rats correlated with their 8 and 1.3 times greater capacities to form 9-hydroxy(OH)-2-FAA and 7-OH-2-FAA respectively. One week after gonadectomy, the formation of 9-OH-2-FAA, the major metabolite in the male, was decreased by 70%, whereas in the female it was increased 1.3 times. Treatment of male rats with beta-naphthoflavone (beta-NF) increased the formation of phenolic metabolites and N-OH-2-FAA, but decreased that of 9-OH-2-FAA. The amounts of 9-OH-2-FAA were increased, however, in beta-NF-treated female and gonadectomized male rats. These sex hormone- and beta-NF-mediated differences in the extent of 9-hydroxylation of 2-FAA are discussed in relation to the fluctuations in the levels of specific cytochrome P-450 isozymes. In contrast to the phenolic metabolites and N-OH-2-FAA, 9-OH-2-FAA was a poor substrate for UDP-glucuronyltransferase; this conjugation was not induced by treatment of male rats with beta-NF. Hence, in the presence of male hormones, relatively large amounts of 9-OH-2-FAA were formed and possibly retained in the liver. A role of this alcohol as a potential promoter in hepatocarcinogenesis by 2-FAA is suggested.

2-Acetylaminofluorene↗
PubMed1989

Drug metabolism by periportal and perivenous rat hepatocytes. Comparison of phase I and phase II reactions and their inducibility during culture.

Hepatocytes were aseptically isolated from either the periportal (pp; zone 1) or the perivenous (pv; zone 3) region by digitonin-collagenase perfusion and cultured on type I collagen for 4 to 9 days. In freshly isolated cells the pp:pv activity ratios of the acinar marker enzymes gamma-glutamyltranspeptidase (gamma-GT), alanine aminotransferase (ALAT) and glutamate dehydrogenase (GLDH) were 2.8, 1.6 and 0.76, respectively. During culture ALAT and GLDH activities gradually declined, but the pp-pv difference was retained for at least 4 days. In contrast, the difference in the gamma-GT activity was rapidly lost, due to its fast initial activation in pv cells. The initial 7-ethoxycoumarin O-deethylase (ECDE) activity was higher in pv cells; this difference was retained for several days of culture and was increased by induction in vitro with either phenobarbital (PB) or beta-naphthoflavone (beta NF). Although the basal UDP-glucuronyltransferase (UDPGT) activity with either p-nitrophenol (pNP) or hydroxybiphenyl (HBP) as substrate did not differ significantly, the in-vitro PB- or beta NF-induced activity was higher in pv cells. Both glucuronidation and sulfation of methylumbelliferone tended to be higher in pv cells. Glutathione S-transferase was initially significantly higher in pv cells and this difference was augmented after in vitro induction by PB or beta NF. After six days in culture all the observed pp-pv differences had disappeared. These results suggest that hepatocytes isolated from the perivenous region seem to maintain their initially higher capacity for phase I and phase II drug reactions during culture and also respond more strongly than periportal cells to in vitro induction.

7-Alkoxycoumarin O-Dealkylase↗
PubMed1993

Phase I and phase II xenobiotic reactions and metabolism of the food-borne carcinogen 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline in aggregating liver cell cultures.

Aggregating fetal liver cell cultures were tested for their ability to metabolize xenobiotics using ethoxycoumarin-O-deethylase (ECOD), as marker of phase I metabolism, and glutathione S-transferase (GST), as marker for phase II reactions. Significant basal activities, stable over 14 days in culture were measured for both ECOD and GST activities. The prototype cytochrome P450 inducers, 3-methylcholanthrene (3-MC) and phenobarbital (PB), increased ECOD and GST activities reaching an optimum 7 days after culturing, followed by a decline in activity. This decline was partially prevented by 1% dimethyl sulfoxide (DMSO) added chronically to the culture medium. DMSO was also found to induce ECOD activity and to a lesser extent GST activity. Furthermore, it potentiated in a dose-dependent manner the induction of ECOD by PB. The food-borne carcinogen 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx) is metabolically transformed through a number of pathways in vivo. It was therefore used to examine the metabolic capacity in fetal and adult liver cell aggregates. Metabolism of MeIQx was mainly through N2-conjugation, resulting in formation of the N2-glucuronide and sulfamate conjugates for non-induced fetal liver cells. These metabolites were also found in large amounts in non-induced adult liver cells. Low levels of cytochrome P450-mediated ring-hydroxylated metabolites were detected in both non-induced fetal and adult liver cells. After induction with arochlor (PCB) or 3-MC, the major pathway was ring-hydroxylation (cytochrome P450 dependent), followed by conjugation to beta-glucuronic or sulfuric acid. The presence of the glucuronide conjugate of N-hydroxy-MeIQx, a mutagenic metabolite, suggested an induction of P450 CYP1A2. The metabolism of MeIQx by liver cell aggregates is very similar to that observed in vivo and suggests that aggregating liver cell cultures are a useful model for in vitro metabolic studies in toxicology.

7-Alkoxycoumarin O-Dealkylase↗
PubMed1986

Obstruction of the swing phase during gait: phase-dependent bilateral leg muscle coordination.

We have investigated bilateral leg muscle activation following an obstruction of the forward swinging leg during gait. When the holding impulse was released at the beginning of the swing phase, weak gastrocnemius (GM) and biceps femoris (BF) responses appeared in the contralateral, standing leg. When the holding impulse was released at the end of the swing phase, strong tibialis anterior (TA) and rectus femoris (RF) responses appeared in the swinging leg, and GM and BF responses in the standing leg. In the latter condition the TA response was followed by a premature impact associated with a GM activation. The latency between onset of impulse and appearance of the responses was 65-70 ms in both legs. While in the first condition the duration of GM and BF response corresponded to the duration of the impulse, it was independent for the duration of GM and BF response in the latter. It is concluded that different strategies for compensation are at work. In the first condition, body stability is maintained during the obstruction by the standing leg. In the second condition, body support is provided by a premature touchdown of the swinging leg. It is suggested that the appropriate pattern is, in part, released by a spinal generator.

Adult↗
PubMed1995

Discrimination between phase-locked and non-phase-locked event-related EEG activity.

Differentiation between phase-locked and non-phase-locked event-related EEG activity is an important task in the evaluation of event-related EEG activity. Event-related changes of EEG activity such as event-related desynchronization (ERD) or event-related synchronization (ERS) can be quantified by either instantaneous band power or intertrial variance calculations. In the former case the ERD or ERS can be masked by an event-related potential while in the latter it is not. Examples from sensory stimulation and movement experiments, where the ERD (ERS) is calculated by both methods, are shown and discussed.

Alpha Rhythm↗
PubMed1992

Separation of oxidized human growth hormone variants by reversed-phase high-performance liquid chromatography. Effect of mobile phase pH and organic modifier.

Human growth hormone (hGH), a polypeptide of 191 amino acids, contains three methionine residues, two of which are susceptible to oxidation by both chemical and photochemical means (Met14 and Met125). To date, no method has existed for resolving the various mono- and di-oxidation products. We report on the resolution of these oxidized variants and native hGH at weakly (pH 3.5) acidic pH. Although all of the oxidized species can be resolved at pH 3.5, use of low pH and neutral pH mobile phases confer some advantages. For example, the Met14 oxidized variant (MetSO-14) and native hGH are best resolved at neutral pH and the mono-oxidized variants (MetSO-125 and MetSO-14) are best resolved at low pH. The effect of organic modifier on the separation of the oxidized variants was also evaluated. 1-Propanol was more effective than acetonitrile in the separation of MetSO-14 and native hGH while acetonitrile was more effective than 1-propanol in the separation of MetSO-125 and MetSO-14. In summary, mobile phase pH and organic modifier were shown to be important parameters in the separation of oxidized hGH variants.

Chromatography, High Pressure Liquid↗
PubMed1992

Measurement of amino acid compositions of glycoprotein systems by gas-phase hydrolysis and reversed-phase high-performance liquid chromatography.

Interest in glycoproteins and their compositions has increased in recent years. Work described in this report illustrates the use of an amino acid analysis protocol involving gas-phase hydrolysis and reversed-phase high-performance liquid chromatography of glycoprotein systems at microgram levels. In other amino acid analysis protocols the problem of losses of amino acids of glycoproteins has been documented. These losses were due to various reactions, referred to as browning or Maillard reactions, which yielded a residue from which amino acids were not recoverable. In our work, three glycoprotein systems are examined: ovalbumin, sICAM-1, and bovine serum albumin--which is naturally unglycosylated, but is spiked with about 30% saccharides. In all three cases, the compositional agreement between the molar ratio of amino acids determined empirically and that predicted is greater than 90%. Thus it is shown that the adverse effects of Maillard-type reactions are avoided, and the presence of carbohydrates causes negligible interferences with amino acid analysis performed under the conditions described herein.

Amino Acids↗
PubMed1993

Resolution of chiral cannabinoids on amylose tris(3,5-dimethylphenylcarbamate) chiral stationary phase: effects of structural features and mobile phase additives.

The separation of six pairs of chiral cannabinoids was achieved using a dimethylphenylcarbamate derivative of amylose, immobilized on silica gel (ChiralPak AD, Daicel), using 2-propanol and ethanol as the modifiers of n-hexane in the mobile phase. Good separation was achieved for most of the solutes in both solvent systems under various conditions. The chromatographic parameters of various cannabinoids in the two solvent systems were determined. The pairs differ from each other in small structural features such as the degree of saturation, position of a double bond and closure of a pyran ring. Therefore, a comparative study could give some clues regarding the mechanism of discrimination between the enantiomeric pairs on the chiral stationary phase. Preliminary measurements of limit of determination showed that it was possible to assess 99.9% enantiomeric purity of the cannabinoids, owing to the high efficiency of the separation. Enantiomers of two monoterpenes, used as intermediates or as starting materials in the chiral synthesis of cannabinoids, were also separated, hence the described procedure is capable of assessing whether the chiral centres in the molecules were sustained throughout the synthetic procedures.

Amylose↗