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Biomedical subjects

M Valiente

Publications and source records attributed to M Valiente.

16 recordsLinked to original sources
PubMed2006

Influence of concomitant food intake on the excretion of orally administered myo-inositol hexaphosphate in humans.

myo-Inositol hexaphosphate (InsP6) widely occurs in plant seeds. At present, some important benefits of InsP6 for human health have been described. The purpose of this study was to find the best condition for the optimum absorption of orally administered InsP6, evaluated by InsP6 urinary excretion. The influence of different stomach conditions (empty, empty with an alkalinizing agent, and full stomach) on the effects of oral administration of InsP6 and its urinary excretion was investigated in six healthy subjects on an InsP6-poor diet, given 400 mg of calcium/magnesium salt of InsP6 as a single dose. The basal urinary excretion of InsP6 on an InsP6-poor diet (50.91 +/- 15.09 microg) was significantly lower than that found when an InsP6-normal diet was consumed (100.09 +/- 26.42 microg) (P < .05). No differences were observed in the areas under the curve of accumulated excretion at 8 hours among the three different stomach conditions studied, suggesting that the overall InsP6 absorption took place independently of the stomach state (full or fasted) and indicating that the InsP6 absorption also takes place during the intestinal transit. Thus, if InsP6 supplements of vegetal origin are consumed to maintain the optimum InsP6 levels needed for a healthy status, these supplements can be consumed either during or between meals with the same efficacy.

Absorption↗
PubMed2005

The effect of octyl glucoside on rheological behavior of diluted and concentrated lamellar phases.

We have investigated the rheological properties of lamellar liquid crystal formed by nonionic surfactants at low and high surfactant concentrations with a small amount of octyl glucoside and their relationship with the topology of the bilayer. Rheology is a specific signature of each bilayer topology. The decrease in viscosity by increasing the shear rate according to a power law with exponent close to -0.8 was found for the concentrated system of LSB/1-butanol/water and 1% in weight of OG. On the contrary, the decrease in the viscosity by increasing the shear rate for the diluted system is less pronounced with lower exponent values. The rheological data agrees with the presence of vesicles. A special case is the system with benzyl alcohol. The apparent viscosity does not follow the same power law than for alkanols.

1-Butanol↗
PubMed2005

Effects of trace metals on the inhibition of calcium oxalate crystallization.

The aim of this study was to examine the possible effects of some trace metals on the inhibition of calcium oxalate crystallization. A test of urinary lithogenic risk was used to follow the crystallization of calcium oxalate from artificial urine in the presence of several metal ions assayed in their physiological concentrations. Interactions of these metal ions with known inhibitors of such crystallization (phytate, pyrophosphate, citrate and chondroitin sulphate) were also investigated. None of the metals affected the inhibition of calcium oxalate crystallization at concentrations approximating those found in normal urine, with the exception of the Fe3+ ions. Interactions of Fe3+ with some urinary components produced both synergic (phytate and pyrophosphate) and negative (citrate) effects on preventing crystallization. These effects are explained in terms of the affinity of the inhibitors for the calcium oxalate crystal surface and their ability to form stable complexes in urine. Because of the minimal concentrations, we conclude that physiological concentrations of trace elements in urine have no significant influence on calcium oxalate crystallization. In this sense, ferric ions, which exhibit an intrinsic high inhibitory capacity of calcium oxalate crystallization at physiological concentrations, even increased by the concomitant presence of phytate and pyrophosphate, are probably unable to act as powerful inhibitors in the presence of physiological urinary concentrations of citrate, due to the formation of highly stable complexes in solution without inhibitory activity.

Calcium Oxalate↗
PubMed2004

Determination of pollution trends in an abandoned mining site by application of a multivariate statistical analysis to heavy metals fractionation using SM&T-SES.

The mobility, availability and persistence of Heavy Metals (HMs), As, Cd, Cu, Ni, Pb and Zn, in contaminated soils of a former abandoned mining area were evaluated by means of a sequential extraction scheme (SES) and applying a multivariate statistical analysis to the obtained data. Chemical partitioning of HMs in each sample was determined in four fractions (acid-soluble, reducible, oxidable and residual) following the Standard Measurements and Testing (SM&T) SES, formerly BCR-SES. Statistical evaluation of results by pattern recognition techniques allowed identification of groups of samples with similar characteristics and observations of correlations between variables, determining the pollution trends and distribution of HMs within the studied area. Typical metal-fraction association and metal availability characteristics of heavy metals have been depicted. The obtained results indicate an urgent need to attenuate the hazard in that area posed by high concentrations of toxic metals, which exceed the limits specified by different European legislations on soil reclamation.

Chemistry Techniques, Analytical↗
PubMed2004

Facilitated transport of Hg(II) through novel activated composite membranes.

The results presented in this work deal with the prime application of activated composite membranes (ACMs) for the transport of Hg(II) ions in a continuous extraction-re-extraction system using di-(2-ethylhexyl)dithiophosphoric acid (DTPA) as carrier. The effects of variables such as the pH, the nature of the acid and the concentration of the casting solutions on the transport of Hg(II) are also investigated. When the ACM was prepared with a 0.5 M DTPA solution and when the feed solution contained 2.5x10(-4) M Hg(II) in 0.1 M HCl, the amount of mercury extracted was greater than 76%. The re-extracted mercury was subsequently recovered by means of a stripping phase comprising 0.3 M thiourea solution in 2 M H2SO4, yielding 54% of the initial amount of mercury after transport had taken place for 180 min.

Journal Article↗
PubMed2004

Vascular activity of (-)-anonaine, (-)-roemerine and (-)-pukateine, three natural 6a(R)-1,2-methylenedioxyaporphines with different affinities for alpha1-adrenoceptor subtypes.

We have studied the mechanism of action of three 6a( R)-1,2-methylenedioxyaporphines as vasorelaxant compounds. The alkaloids assayed showed different affinities for the three human cloned alpha (1)-adrenoceptor (AR) subtypes stably expressed in rat-1 fibroblasts, showing lower affinity for alpha(1B)-AR with regard to the alpha(1A)- or alpha(1D)-subtypes. These three natural compounds are more potent inhibitors of [ (3)H]-prazosin binding than of [ (3)H]-diltiazem binding to rat cerebral cortical membranes. As all these alkaloids inhibited noradrenaline (NA)-induced [ (3)H]-inositol phosphate formation in cerebral cortex and rat tail artery, they may be safely viewed as alpha (1)-AR antagonists, as is demonstrated by the vasorelaxant responses observed in isolated rat tail artery and/or aorta precontracted with NA. The alkaloids also inhibited the contractile response evoked by KCl (80 mM) but with a lower potency than that shown against NA-induced contraction. We have also examined their ability to inhibit the different forms of cyclic nucleotide phosphodiesterases (PDE) isolated from bovine aortic smooth muscle and endothelial cells, with negative results. We conclude that N-methylation favours the interaction of (R)-aporphines with all alpha (1)-AR subtypes, and that the topography of the binding site recognizing the basic or protonated nitrogen atom is similar in all three alpha (1)-AR subtypes. The presence of a hydroxy group at C-11 has different effects on the affinity for each alpha (1)-AR subtype but decreases the affinity for Ca (2+) channels. These results confirm and extend the view that subtle changes in the hydroxylation patterns on the aromatic ring of the aporphine structure affect the interactions of these compounds with the three alpha (1)-AR subtypes in different ways, suggesting that the binding site recognizing the aporphine skeleton is different in each of the three subtypes.

Alkaloids↗
PubMed2003

The effect of resin particle size on the rate of ion release: interactions in mixed bed systems.

The aim of the present study is to evaluate the influence of resin particle sizes on the rate of ions release from a mixture of ion-exchange resins (named NMTD) which supplies calcium, fluoride, and phosphate ions as the main mineral content, and to elucidate the different phenomena taking place through the related ion-exchange process. The final goal of the study, related to dental application (enamel restoration), is to limit the particle size range, since the rate of ion release is a key parameter in the successful achievement of such objective. Weak-type ion-exchange resins, loaded with the appropriate ions, were ground and sieved into granulometric fractions of bead diameters of 0.1-0.075, 0.075-0.063, and 0.063-0.05 mm. Particle size was controlled by a laser diffraction particle distribution analyzer. The experiments on the kinetics of ions release were carried out under batch conditions in artificial saliva desorption solution thermostatized at 37 degrees C. The release of Ca(2+) and F(-) was determined by corresponding ion-selective electrodes automatically controlled, whereas H(2)PO(4)(-) was measured spectrophotometrically by the inductively coupled plasma-optical emission technique (ICP-OES). The results of this study show that the process of ion-exchange for the different particle size fractions of resins is critical for the study of the kinetics release of the ions immobilized in the corresponding mixed bed polymeric matrices. In fact, despite the apparent narrow range of particle sizes of the mixed bed systems studied, appreciable differences in the rate of ions release are obtained. Since the ion release rate is depending on the contact surface, an increase of factor of 2 in particle size represents an increase of an order of magnitude of the resin contact surface due to the resin porosity. In this concern, it has been observed that the rate of ions release increases when particle size decreases. The interactions occurring during the ion release from the mixed bed resins (containing calcium-, fluoride-, and phosphate-loaded resins) can be interpreted by the following phenomena: H(2)PO(4)(-), which hardly modifies its rate of release in the presence of Ca(2+) and F(-) in the mixture, promotes a considerable increase in the rate of Ca(2+) release due to the formation of a calcium dihydrogen phosphate soluble complex. F(-) also produces an acceleration in the rate of Ca(2+) release due to the formation of solid CaF(2 )on the surface of cationic resin particles, which in contrast leads to a decrease in the rate of F(-) release.

Journal Article↗
PubMed2000

Effects of Cetylpyridinium Chloride on Phase and Rheological Behavior of the Diluted C(12)E(4)/Benzyl Alcohol/Water System.

The influence of a small amount of cetylpyridinium chloride on the phase diagram of the diluted C(12)E(4)/benzyl alcohol/water system is studied. The presence of the ionic surfactant results in the stabilization of the vesicles in relation to the open bilayers. The bilayer structures are less sensitive to shear effects than for the system without cationic surfactant. Moreover, the formation of the mixed micelle phase is also favored. The transition from spherical to rod micelles has been detected from viscosity measurements. The micelles located close to the two-phase region (at the lower amount of cationic surfactant) are the largest and most flexible micelles. Copyright 2000 Academic Press.

Journal Article↗
PubMed2000

Ion exchange on resins with temperature-responsive selectivity III. Influence of complex formation stoichiometry on temperature dependence of resin selectivity.

The influence of temperature (293 308 K 1:1 IDA:Ni2+ complex is dominating. The Cu2+-Ni2+ exchange equilibrium from sulfate medium is characterized by the formation of nickel complexes of both stoichiometries within the whole temperature range studied. The dependence of alpha on T in Zn2+-Co2+ exchange system has been shown to be weaker than that in the Cu2+-Ni2+ system. This result is in a good agreement with the predictions made in the first communication of this series. The results of thermostripping experiments carried out for Cu2+-Co2+ exchange have shown that the efficiency of the thermostripping process depends on both the interval of working temperatures (deltaT) and its position on the temperature scale. The efficiency of thermostripping rises with an absolute deltaT value and also increases following the shift of temperature interval to the lower temperature range.

Hydrogen-Ion Concentration↗
PubMed2000

Ion exchange on resins with temperature-responsive selectivity IV. Influence of solution and column parameters on efficiency of reagentless separation of copper and zinc using thermo-induced concentration waves technique.

The effect of solution and column parameters such as pH, ratio of metal ions and the height of resin bed on formation of the thermo-induced concentration waves (TICW) in the course of the thermostripping process of Cu2+ and Zn2+ ions from iminodiacetic resin Lewatit TP-207 has been studied. The formation of TICW is attributed by both different diffusivities of metal ions and the presence of the third (H+) ion in the system. This effect makes it possible to carry out a reagentless separation of metal ions by using either the metal depletion or metal concentration mode of operation. The efficiency of the TICW-based separation process by using the metal depletion mode appears to be the higher the lower relative concentration of metal ion under removal (slower diffusing ionic species). The mathematical model proposed allows for qualitative and quantitative description of thermostripping processes in a wide range of pH and solution compositions. The physical model of the TICW process proposed makes it possible to account for the influence of different process parameters and generalise the applicability of the TICW separation technique to the binary mixtures of any metal ions with different diffusivities.

Chromatography, Ion Exchange↗
PubMed1999

Ultrasonic Study of the L Phase of the CTAB/Benzyl Alcohol/Water System.

The L phase of the ternary CTAB/benzyl alcohol/water system that extends from the water corner to the alcohol corner was studied by the sound velocity method which indicated variations in velocity when the aggregate structure changed from normal micelles in water to reverse micelles in the alcohol corner of the phase diagram. From these results it was concluded that the transition from normal to reverse micelles takes place while passing through two different bicontinuous regions, one of them with alcohol micro domains dispersed in water and the other one as a bicontinuous reverse region with the predominance of the water domains dispersed in alcohol. Copyright 1999 Academic Press.

Journal Article↗
PubMed1998

Structural Changes in the Isotropic Phase of the Ternary Surfactant System: Tetradecyldimethylamine Oxide/Benzyl Alcohol/Water.

The surfactant system tetradecyldimethylamine oxide (TDMAO)/benzyl alcohol/water has been studied. In the phase diagram of this ternary system a large isotropic region is encountered that connects the water corner to the benzyl alcohol corner. This isotropic phase has been investigated in some detail by means of electric conductivity, viscosity, electric birefringence, and small-angle neutron scattering (SANS) measurements. From these experiments it can be concluded that for roughly equal amounts of alcohol and water a bicontinuous structure is present, similar to that typically observed for bicontinuous microemulsions. The structural units present become continuously smaller with increasing alcohol content, and at very high alcohol content only small reverse aggregates are present. The formation of this bicontinuous phase can be understood by the fact that the presence of the benzyl alcohol reduces the stiffness of the surfactant film, and therefore such a "sponge"-type structure is favored. With increasing surfactant concentration the amphiphilic film becomes stiffer again, which leads to the formation of a lamellar phase. The corresponding phase boundary is exactly related to the amphiphilicity factor as it can be deduced from the scattering experiments. Copyright 1998 Academic Press.

Journal Article↗
PubMed1998

Study of the Cetyltrimethylammonium Bromide/ 1,6-Hexanediol/Water System.

The phase diagram of the ternary system CTAB/1,6-hexanediol/water was obtained at 25.0 +/- 0.1 degreesC. The system shows a clear, isotropic, and low-viscosity region, the L phase, and a liquid-crystalline phase characterized as hexagonal phase H1. The L phase was characterized by conductivity and steady-state fluorescence quenching measurements in order to determine the kind of aggregate that exists in this region. The basic hydrolysis of crystal violet was also studied in the L phase. Both the L phase properties and the phase diagram indicate the 1,6-hexanediol behaves as a short-chain alkanol. Copyright 1998 Academic Press.

Journal Article↗
PubMed1997

Relationships between structure and vascular activity in a series of benzylisoquinolines.

1. In the present work, the properties of 3-methyl isoquinoline, 3,4-dihydropapaverine, tetrahydropapaverine and tetrahydropapaveroline were compared with those of papaverine and laudanosine. The work includes functional studies on rat isolated aorta contracted with noradrenaline, caffeine or KCl, and a determination of the affinity of the compounds for alpha1-adrenoceptors and calcium channel binding sites, with [3H]-prazosin, [3H]-nitrendipine and [3H]-(+)-cis-diltiazem binding to rat cerebral cortical membranes. The effects of papaverine derivatives on the different molecular forms of cyclic nucleotide phosphodiesterases (PDE) isolated from bovine aorta were also determined. 2. The three papaverine derivatives show greater affinity than papaverine for the [3H]-prazosin binding site. They are therefore more selective as inhibitors of [3H]-prazosin binding as opposed to [3H]-(+)-cis-diltiazem, while papaverine appears to have approximately equal affinity for both. [3H]-nitrendipine binding was not affected by either papaverine or papaverine derivatives in concentrations up to 100 microM. 3-Methylisoquinoline had no effect on any of the binding sites assayed. 3. Contractions evoked by noradrenaline (1 microM) in rat aorta were inhibited in a concentration-dependent manner by 3,4-dihydropapaverine, tetrahydropapaverine and with a lower potency, by tetrahydropapaveroline. In Ca2+-free solution, tetrahydropapaverine and to a lesser extent, tetrahydropapaveroline, inhibited the noradrenaline (1 microM) evoked contraction in a concentration-dependent manner and did not modify the phasic contractile response evoked by caffeine (10 mM). This suggests that these alkaloids do not act at the intracellular level, unlike papaverine which inhibits the contractile response to caffeine and noradrenaline. 4. Inositol phosphates formation induced by noradrenaline (1 microM) in rat aorta was inhibited by tetrahydropapaverine (100 microM) and tetrahydropapaveroline (300 microM), thus suggesting that alpha1D-adrenoceptors are coupled to phosphoinositide metabolism in rat aorta. 5. Unlike papaverine, which has a significant effect on all the PDE isoforms, the three alkaloids assayed did not have an inhibitory effect on the different forms of PDE isolated from bovine aorta. 6. These results provide evidence that papaverine derivatives with a partially or totally reduced isoquinoline ring have a greater affinity for alpha1-adrenoceptors and a lower affinity for benzothiazepine sites in the Ca2+-channel than papaverine. This structural feature also implies a loss of the inhibitory activity on PDE isoforms. The planarity of the isoquinoline ring (papaverine) impairs the interaction with the alpha1-adrenoceptor site and facilitates it with the Ca2+-channels and PDEs, whereas the more flexible tetrahydroisoquinoline ring increases the binding to alpha1-adrenoceptors.

3',5'-Cyclic-AMP Phosphodiesterases↗