Showing papers by "University of Extremadura published in 2000"

Clinically significant pharmacokinetic interactions between dietary caffeine and medications.

Abstract: Caffeine from dietary sources (mainly coffee, tea and soft drinks) is the most frequently and widely consumed CNS stimulant in the world today Because of its enormous popularity, the consumption of caffeine is generally thought to be safe and long term caffeine intake may be disregarded as a medical problem However, it is clear that this compound has many of the features usually associated with a drug of abuse Furthermore, physicians should be aware of the possible contribution of dietary caffeine to the presenting signs and symptoms of patients The toxic effects of caffeine are extensions of their pharmacological effects The most serious caffeine-related CNS effects include seizures and delirium Other symptoms affecting the cardiovascular system range from moderate increases in heart rate to more severe cardiac arrhythmia Although tolerance develops to many of the pharmacological effects of caffeine, tolerance may be overwhelmed by the nonlinear accumulation of caffeine when its metabolism becomes saturated This might occur with high levels of consumption or as the result of a pharmacokinetic interaction between caffeine and over-the-counter or prescription medications The polycyclic aromatic hydrocarbon-inducible cytochrome P450 (CYP) 1A2 participates in the metabolism of caffeine as well as of a number of clinically important drugs A number of drugs, including certain selective serotonin reuptake inhibitors (particularly fluvoxamine), antiarrhythmics (mexiletine), antipsychotics (clozapine), psoralens, idrocilamide and phenylpropanolamine, bronchodilators (furafylline and theophylline) and quinolones (enoxacin), have been reported to be potent inhibitors of this isoenzyme This has important clinical implications, since drugs that are metabolised by, or bind to, the same CYP enzyme have a high potential for pharmacokinetic interactions due to inhibition of drug metabolism Thus, pharmacokinetic interactions at the CYP1A2 enzyme level may cause toxic effects during concomitant administration of caffeine and certain drugs used for cardiovascular, CNS (an excessive dietary intake of caffeine has also been observed in psychiatric patients), gastrointestinal, infectious, respiratory and skin disorders Unless a lack of interaction has already been demonstrated for the potentially interacting drug, dietary caffeine intake should be considered when planning, or assessing response to, drug therapy Some of the reported interactions of caffeine, irrespective of clinical relevance, might inadvertently cause athletes to exceed the urinary caffeine concentration limit set by sports authorities at 12 mg/L Finally, caffeine is a useful and reliable probe drug for the assessment of CYP1A2 activity, which is of considerable interest for metabolic studies in human populations

Problems of inference for Azzalini's skewnormal distribution

Abstract: This paper considers various unresolved inference problems for the skewnormal distribution We give reasons as to why the direct parameterization should not be used as a general basis for estimation, and consider method of moments and maximum likelihood estimation for the distribution's centred parameterization Large sample theory results are given for the method of moments estimators, and numerical approaches for obtaining maximum likelihood estimates are discussed Simulation is used to assess the performance of the two types of estimation We also present procedures for testing for departures from the limiting folded normal distribution Data on the percentage body fat of elite athletes are used to illustrate some of the issues raised

Critical behavior of the three-dimensional Ising spin glass

Abstract: We have simulated, using parallel tempering, the three-dimensional Ising spin glass model with binary couplings in a helicoidal geometry. The largest lattice (L520) has been studied using a dedicated computer (the SUE machine). We have obtained, measuring the correlation length in the critical region, strong evidence for a second-order finite-temperature phase transition, ruling out other possible scenarios like a KosterlitzThouless phase transition. Precise values for the ν and ƞ critical exponents are also presented.

Potential energy surface, thermal, and state-selected rate coefficients, and kinetic isotope effects for Cl+CH4→HCl+CH3

Abstract: A new potential energy surface is reported for the gas-phase reaction Cl+CH4→HCl+CH3. It is based on the analytical function of Jordan and Gilbert for the analog reaction H+CH4→H2+CH3, and it is calibrated by using the experimental thermal rate coefficients and kinetic isotope effects. The forward and reverse thermal rate coefficients were calculated using variational transition state theory with semiclassical transmission coefficients over a wide temperature range, 200–2500 K. This surface is also used to analyze dynamical features, such as reaction-path curvature, the coupling between the reaction coordinate and vibrational modes, and the effect of vibrational excitation on the rate coefficients. We find that excitation of C–H stretching modes and Cl–H stretching modes enhances the rate of both the forward and the reverse reactions, and excitation of the lowest frequency bending mode in the CH4 reactant also enhances the rate coefficient for the forward reaction. However, the vibrational excitation of t...

Effects of Tillage, Crop Rotation, and Nitrogen Fertilization on Wheat under Rainfed Mediterranean Conditions

Abstract: The combined long-term effects of tillage method, crop rotation, and N fertilizer rates on grain yield have not been studied in rainfed systems under Mediterranean climates. As part of a long-term experiment started in 1986, a field study was conducted between 1994 and 1998 to determine the effects of tillage (TILL), crop rotation (ROT), and N fertilization on wheat (Triticum aestivum L.) growth and yield in a rainfed Mediterranean region. Tillage treatments included no tillage (NT) and conventional tillage (CT). Crop rotations were wheat-sunflower (Helianthus annuus L.) (WS), wheat-chickpea (Cicerarietinum L.) (WCP), wheat-faba bean (Vicia faba L.) (WFB), wheatfallow (WF), and continuous wheat (CW). Nitrogen fertilizer rates were 0, 50, 100, and 150 kg N ha -1 on a Vertisol (Typic Haploxerert). A split-split plot design with four replications was used. Heavy rainfall during this research negatively impacted vegetative growth and grain yield of the wheat due to waterlogging. Wheat yield in the wet years was lower under NT than under CT. Yield decreased in the following crop rotation sequence: WFB » WF > WS > WCP » CW. Wheat responded to N fertilizer at rates up to 100 kg N ha -1 in the wet years but exhibited no response in the dry years. Yield under CT was higher at all N rate applied to wheat. The effect of N fertilizer on yield was more marked for the rotations with no legumes. The incorporation of the results for the 4-yr period to those of the long-term experiment provides more consistent information on the characterization and performance of the various systems.

Computer simulation of uniformly heated granular fluids

Abstract: Direct Monte Carlo simulations of the Enskog-Boltzmann equation for a spatially uniform system of smooth inelastic spheres are performed. In order to reach a steady state, the particles are assumed to be under the action of an external driving force which does work to compensate for the collisional loss of energy. Three different types of external driving are considered: (a) a stochastic force, (b) a deterministic force proportional to the particle velocity and (c) a deterministic force parallel to the particle velocity but constant in magnitude. The Enskog-Boltzmann equation in case (b) is fully equivalent to that of the homogeneous cooling state (where the thermal velocity monotonically decreases with time) when expressed in terms of the particle velocity relative to the thermal velocity. Comparison of the simulation results for the fourth cumulant and the high energy tail with theoretical predictions derived in cases (a) and (b) [T. P. C. van Noije and M. H. Ernst, Gran. Matt. 1, 57 (1998)] shows a good agreement. In contrast to these two cases, the deviation from the Maxwell-Boltzmann distribution is not well represented by Sonine polynomials in case (c), even for low dissipation. In addition, the high energy tail exhibits an underpopulation effect in this case.

Evaluation of caffeine as an in vivo probe for CYP1A2 using measurements in plasma, saliva, and urine.

Abstract: Twenty-five healthy volunteers were given 100 mg caffeine orally and several estimates of cytochrome P450 1A2 (CYP1A2) activity were evaluated. The validation was performed by correlation of different parameters in plasma, saliva, and urine to two measures of caffeine clearance, CL on and CL 137X→17X that served as standards of reference. Two subjects were excluded because of noncompliance with a caffeine-free diet. In the remaining 23 subjects, both plasma and saliva total clearances of caffeine were highly correlated with each other (r s = 0.97, p < 0.0001). The ratio 17X/137X restricted to one sampling point taken 4 hours after dose, showed a high correlation (r s ) with CL oral and CL 137X→17X in plasma (0.84/0.83) and saliva (0.82 / 0.77) (p < 0.0001 for all the correlation values) where 17X is 1,7--dimethylxanthine (paraxanthine) and 137X is 1,3,7-trimethylxanthine (caffeine). Additionally, the ratio (AFMU + IU + IX + 17U + 17X)/137X in a 0-24 hours urine sampling showed the highest correlation with CL 137X→17X (r s = 0.85, p < 0.001) where AFMU is 5-acetylamino-6-formylamino-3-methyluracil, 1U is 1-methyluracil, 1X is 1-methylxanthine, and 17U is 1,7-dimethyluric acid. The major estimates of CYP1A2 activity were significantly less in nonsmoking females, and this probably was related to the use of oral contraceptives in this subpopulation. In summary, among caffeine-based approaches for CYPI A2, the authors recommend either plasma or saliva 17X/137X ratio and the urinary (AFMU + IU + IX + 17U + 17X)/137X ratio during a sampling interval of at least 8 hours, starting at time zero since caffeine intake. These indices are simple, reliable, and relatively inexpensive estimates of CYP1A2 activity to be used in the study of human populations.

Computer simulation of uniformly heated granular fluids

Abstract: Direct Monte Carlo simulations of the Enskog-Boltzmann equation for a spatially uniform system of smooth inelastic spheres are performed In order to reach a steady state, the particles are assumed to be under the action of an external driving force which does work to compensate for the collisional loss of energy Three different types of external driving are considered: (a) a stochastic force, (b) a deterministic force proportional to the particle velocity and (c) a deterministic force parallel to the particle velocity but constant in magnitude The Enskog-Boltzmann equation in case (b) is fully equivalent to that of the homogeneous cooling state (where the thermal velocity monotonically decreases with time) when expressed in terms of the particle velocity relative to the thermal velocity Comparison of the simulation results for the fourth cumulant and the high energy tail with theoretical predictions derived in cases (a) and (b) [T P C van Noije and M H Ernst, Gran Matt 1, 57 (1998)] shows a good agreement In contrast to these two cases, the deviation from the Maxwell-Boltzmann distribution is not well represented by Sonine polynomials in case (c), even for low dissipation In addition, the high energy tail exhibits an underpopulation effect in this case

Genetic and environmental components of phenotypic variation in immune response and body size of a colonial bird, Delichon urbica (the house martin).

Abstract: Directional selection for parasite resistance is often intense in highly social host species. Using a partial cross-fostering experiment we studied environmental and genetic variation in immune response and morphology in a highly colonial bird species, the house martin (Delichon urbica). We manipulated intensity of infestation of house martin nests by the haematophagous parasitic house martin bug Oeciacus hirundinis either by spraying nests with a weak pesticide or by inoculating them with 50 bugs. Parasitism significantly affected tarsus length, T cell response, immunoglobulin and leucocyte concentrations. We found evidence of strong environmental effects on nestling body mass, body condition, wing length and tarsus length, and evidence of significant additive genetic variance for wing length and haematocrit. We found significant environmental variance, but no significant additive genetic variance in immune response parameters such as T cell response to the antigenic phytohemagglutinin, immunoglobulins, and relative and absolute numbers of leucocytes. Environmental variances were generally greater than additive genetic variances, and the low heritabilities of phenotypic traits were mainly a consequence of large environmental variances and small additive genetic variances. Hence, highly social bird species such as the house martin, which are subject to intense selection by parasites, have a limited scope for immediate microevolutionary response to selection because of low heritabilities, but also a limited scope for long-term response to selection because evolvability as indicated by small additive genetic coefficients of variation is weak.

From parity to chirality: chemical implications revisited†

Abstract: Parity violation represents an essential property of particle and atomic handedness used to cope with the complex phenomenon of asymmetry in the universe. At the molecular level, however, numerous experiments suggest that parity-violating energy differences have not determined the amplification and propagation of homochirality. Asymmetric transformations conducted under far-from-equilibrium conditions reveal the existence of non-linear autocatalysis which is stochastic in nature. In any event and, globally considered, chirality appears as a unifying characteristic of our visible environment with evolutionary implications, thereby suggesting areas for productive research.

A chloroform extract obtained from a decoction of Ficus carica leaves improves the cholesterolaemic status of rats with streptootocin-includede diabetes

Abstract: The antidiabetic effects of Ficus carica leaf extracts have been reported previously From the aqueous decoction of fig leaves, after treatment with HCI, centrifuging, treatment with sodium hydroxide (NaOH) and extraction with chloroform (CHCl3), the administration of the organic phase rats with streptozotocin-induced diabetes led to a decline in the levels of total cholesterol and an decrease in the total cholesterol/HDL cholesterol ratio (with respect to the control group), together with a reduction of the hyperglycaemia

Sensory characteristics of Iberian ham: Influence of rearing system and muscle location/ Caracteristicas sensoriales del jamón Ibérico: Influencia del sistema de engorde y del músculo:

Abstract: The effects of pig rearing conditions (free-range system based on acorn and pasture versus confinement on a concentrate feed) and muscle location (biceps femoris and semimembranosus) on sensory characteristics of dry-cured Iberian hams were studied. Muscle samples were sensorily evaluated for appearance, texture, aroma and flavor attributes by a trained panel. Muscle location significantly affected texture and appearance traits. Semimembranosus muscle was harder, dryer and more fibrous than was biceps femoris muscle. Rearing conditions significantly affected sensory attributes related to fatty acid composition and lipid content of meat. Hams from free-range pigs showed higher scores in oiliness, brightness of the lean, marbling, and aroma and flavor traits than did hams from pigs raised in confinement.

Sodium Dodecylbenzenesulfonate Removal from Water and Wastewater. 1. Kinetics of Decomposition by Ozonation

Abstract: Ozonation experiments were conducted to investigate the sodium dodecylbenzenesulfonate (NaDBS) removal from aqueous solution and domestic wastewater. The influence of pH and tert-butyl alcohol conc...

Rapid and sensitive determination of 4-nitrophenol, 3-methyl-4-nitrophenol, 4,6-dinitro-o-cresol, parathion-methyl, fenitrothion, and parathion-ethyl by liquid chromatography with electrochemical detection.

Abstract: Liquid chromatography with electrochemical detection has been used to determine various nitropesticides, DNOC, fenitrothion, and parathion (methyl and ethyl), and some of their main metabolites, 4-nitrophenol for parathion (methyl and ethyl) and 3-methyl-4-nitrophenol for fenitrothion, by using indirect detection. Analysis of them in river water samples has been performed without a preconcentration step. The recovery efficiencies of the tested compounds yielded values between 96 and 112% at the fortification level of 0.5 ppb in a river water sample, and their relative standard deviations were between 1 and 15%. The detection limits of these compounds ranged between 0.05 and 0.14 ppb.

Damage‐Resistant Brittle Coatings

Abstract: Laminate structures consisting of hard, brittle coatings andsoft, tough substrates are important in a wide variety of engi-neering applications (cutting tools, electronic multilayers, la-minated windscreens), biological structures (teeth and dentalcrowns, shells, bones), and traditional pottery (ceramicglazes). A hard outerlayer variously offers increased load-bearing capacity, wear resistance, thermal and corrosion pro-tection, electrical insulation, and aesthetics; a compliant un-derlayer offers stress redistribution and damage tolerance.But hard layers are susceptible to cracking, especially in sur-face-concentrated loads from static or cyclic contacts. In nat-ural or restorative tooth structures, for instance, forces in ex-cess of 100 N operate at contacts between opposing cusps ofcharacteristic radii 2–4 mm over 10

The wrapped skew-normal distribution on the circle

Abstract: The wrapped skew-normal distribution is proposed as a model for circular data. Basic results for the distribution are established and estimation for a circular parametrisation of it considered. Procedures based on the sample second central sine moment for testing for departures from three important limiting cases of the distribution are described. The model and some new inferential techniques are applied to directional data from a study into bird migration.

DNA degradation by the mixture of copper and catechol is caused by DNA-copper-hydroperoxo complexes, probably DNA-Cu(I)OOH

Abstract: Free hydroxyl radicals (free ()OH), singlet oxygen ((1)O(2)), or ( )OH produced by DNA-copper-hydroperoxo complexes are possible DNA-damaging reactive oxygen species (ROS) in the reaction system containing copper, catechol, and DNA para-Chlorobenzoic acid (pCBA) degradation studies revealed that CuCl(2) mixed with catechol produced free ()OH In the presence of DNA, however, inhibition of the pCBA degradation suggested that another ROS is responsible for the DNA degradation Of a series of ROS scavengers investigated, only KI, NaN(3), and Na-formate-all of the salts tested-strongly inhibited the DNA degradation, suggesting that the ionic strength rather than the reactivity of the individual scavengers could be responsible for the observed inhibition The ionic strength effect was confirmed by increasing the concentration of phosphate buffer, which is a poor ()OH scavenger, and was interpreted as the result of destabilization of DNA-copper-hydroperoxo complexes Piperidine-labile site patterns in DNA degraded by copper and catechol showed that the mixture of Cu(II) and catechol degrades DNA via the intermediate formation of a DNA-copper-hydroperoxo complex Replacement of guanine by 7-deazaguanine did not retard the DNA degradation, suggesting that the DNA-copper-hydroperoxo complexes do not bind to the guanine N-7 as proposed in the literature