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Showing papers by "University of Extremadura published in 1990"


Journal ArticleDOI
01 Mar 1990-Talanta
TL;DR: A new spectrophotometric method for resolving binary mixtures of salicylic and salicyluric acids is proposed, based on use of the first derivative of the ratios of spectra.

338 citations


Journal ArticleDOI
TL;DR: The results suggest that the goat is an important reservoir of enterotoxigenic staphylococci, most of which produce SEC, which was the SE type most frequently produced.
Abstract: The ability of 342 staphylococcal isolates from different anatomical sites in healthy goats to produce staphylococcal enterotoxins (SE) was investigated. SE were produced by 74.3% of the 70 coagulase-positive strains and by 22% of the coagulase-negative strains studied. Most enterotoxigenic strains were isolated from the skin of udders and teats and from milk. SEC was the SE type most frequently produced, either alone (67.9%) or in combination with others. Five coagulase-negative species not previously reported as SE producers were identified (Staphylococcus chromogenes, S. warneri, S. sciuri, S. saprophyticus, and S. lentus). SEA, SEB, and SEC were detected in the milk of 17 of the 133 healthy goats studied. These results suggest that the goat is an important reservoir of enterotoxigenic staphylococci, most of which produce SEC.

143 citations


Journal ArticleDOI
TL;DR: This paper provides the first evidence for territorial defence of mates in red deer and may contribute to the understanding of the dynamic nature of mating behaviour in ungulates.

116 citations


Journal ArticleDOI
TL;DR: The results reveal that the otic placode undergoes shaping between stages HH9 and HH12; during this period the rostrocaudal axis is shortened, while the lateromedial axis of the placode lengthens, and the coincidence in time between the beginning of intimate otic anlage–rhombencephalon contact and active invagination suggests that these two processes are related.
Abstract: Scanning electron microscopy, light microscopy, and morphometric analysis were used to study the morphological changes of the otic placode and vesicle before and during invagination and closure processes. Our results reveal that the otic placode undergoes shaping between stages HH9 and HH12; during this period the rostrocaudal axis is shortened, while the lateromedial axis of the placode lengthens. The presence of long cytokinesis bridges during this period suggests that cellular displacements after mitosis may participate in the shaping of the otic placode. The shaping process appears to facilitate the approach of the otic placode to the neural tube. From stage HH12 on, the otic anlage gradually becomes a U-shaped structure with its medial portion in intimate apposition to the rhombencephalic neural tube. The coincidence in time between the beginning of intimate otic anlage-rhombencephalon contact and active invagination suggests that these two processes are related. Changes occurring at the edges of the otic vesicle until their disappearance in stage HH17 suggest that, in addition to a process of invagination, the edges of the otic anlage become bent. During closure, cells at the edges of the otic vesicle differ in apical morphology according to their topographical location: The cells between the rostral and lateral edges have elongated apices, in contrast with the polygonal shape of the cell apices in other places of the edges. In the opposite side (between the caudal and medial edges) cell death is observed. Closure of the otic vesicle conceptualized as a zipper-like model is discussed. We propose that early development of the otic anlage takes place in four stages: 1) shaping (stages HH9-11); 2) triggering of the invagination (stage HH12); 3) early invagination and lateral bending (stages HH13-15); and 4) late invagination and closure (stages HH16-17).

67 citations


Journal ArticleDOI
TL;DR: An improved version of the Krylov-Bogoliubov method that gives the approximate solution of the non-linear cubic oscillator x + c 1 x+ c 3 x 3 + ef(x, x dot ) = 0 in terms of Jacobi elliptic functions is described as discussed by the authors.

66 citations


Journal ArticleDOI
TL;DR: Experimental evidence is reported that the mesenchyme lamina is a pretendinous structure that controls the spatial organization of the flexor and extensor tendons of the distal part of the chick leg and defines the position of subsequent tendon development, supporting its role as a pretendedinous structure which might be responsible for the alignment of the pretendinous condensing cells.

61 citations


Journal ArticleDOI
01 Jan 1990-Analyst
TL;DR: The simultaneous determination of salicylic acid in binary and/or ternary mixtures and its two main urinary metabolites is proposed.
Abstract: The simultaneous determination of salicylic acid in binary and/or ternary mixtures and its two main urinary metabolites is proposed. Mixtures of salicylic, salicyluric and gentisic acids are resolved by synchronous spectrofluorimetry, in combination with first-derivative measurements. The urine is extracted with diethyl ether in acid medium. Salicylic and salicyluric acids are re-extracted into glycine-sodium hydroxide buffer solution of pH 11.6 and determined at that pH, and salicylic and gentisic acids are re-extracted into boric acid-sodium hydroxide buffer solution of pH 8.5 and determined at pH 6.

46 citations


Journal ArticleDOI
01 Jan 1990-Carbon
TL;DR: In this paper, the introduction of sulfur on the surface of activated carbon was studied in different experimental conditions and the stability of the surface state was checked against the increase of temperature and outgassing.

46 citations


Journal ArticleDOI
TL;DR: A modified method for the determination of sulphonamides, based on the Bratton-Marshall reaction with derivative spectrophotometry, is proposed in this article, which can be applied to determine sulphonamide in urine, honey and pharmaceutical formulations.

45 citations


Journal ArticleDOI
TL;DR: In this article, a simple, rapid and precise analytical method for sulfathiazole, oxytetracycline and tetracecline residues in honey has been established using micellar reversed-phase high-performance liquid chromatography with photometric detection.
Abstract: A simple, rapid and precise analytical method for sulfathiazole, oxytetracycline and tetracycline residues in honey has been established using micellar reversed-phase high-performance liquid chromatography with photometric detection. The mean recoveries of sulfathiazole, oxytetracycline and tetracycline were 97.7, 95.3 and 100.4%, respectively. Detection limits in honey were 0.9 μg/g for sulfathiazole, 1.2 μg/g for oxytetracycline and 3.0 μg/g for tetracycline.

43 citations


Journal ArticleDOI
TL;DR: Ventricular myocardial fiber architecture has been considered an important factor in heart dynamics but most anatomical studies however have focussed on the analysis of normal hearts.
Abstract: Ventricular myocardial fiber architecture has been considered an important factor in heart dynamics. Most anatomical studies however have focussed on the analysis of normal hearts. The present study c

Journal ArticleDOI
TL;DR: 5-HT is the most potent vasoconstrictor agent of all those tested, whose effects appear to be mediated by 5-HT2- but not by alpha 1-adrenergic receptors; (2) chorionic vessels also possess H1-receptors; and ketanserin has more affinity to block 5- HT2- receptors than to blockalpha 1- adrenergic- and H 1-receptionors.
Abstract: 1. The effect of different vasoactive agents on segments of human chorionic arteries and veins was analyzed. 2. The order of these agents to produce maximal contractile responses was: 5-hydroxytryptamine (5-HT) = histamine (H) = K+ greater than noradrenaline (NA) greater than or equal to phenylephrine (PHEN) greater than clonidine (CLON), and with regard to their potencies (EC50 values) was: 5-HT greater than or equal to NA greater than or equal to H greater than PHEN greater than CLON greater than K+. Dopamine and isoproterenol did not elicit any type of response. 3. The receptors involved on the contractions elicited by agonists were analyzed. 4. The results obtained suggest that: (1) 5-HT is the most potent vasoconstrictor agent of all those tested, whose effects appear to be mediated by 5-HT2- but not by alpha 1-adrenergic receptors; (2) chorionic vessels also possess H1-receptors; and (3) ketanserin has more affinity to block 5-HT2-receptors than to block alpha 1-adrenergic- and H1-receptors.

Journal ArticleDOI
TL;DR: A negative correlation was found between MR of DBQ and age at onset of disease in patients free of drugs known to interact with DBQ metabolism, which could be a genetic factor that delays the clinical onset of Parkinson's disease in predisposed people.
Abstract: Oxidative phenotype and metabolic ratio (MR) of debrisoquine (DBQ) have been determined in 87 patients with Parkinson's disease and in 556 healthy control subjects. Three patients (3.45%) and 34 control subjects (6.12%), having an MR greater than 12.6, were classified as poor metabolisers (PM) of DBQ (ns). The distribution of MR values in the 84 Parkinsonian patients classified as extensive metabolisers (EM) showed a less efficient oxidative rate when compared with controls of the same phenotype (p less than 0.001). This difference may be due to enzymatic inhibition caused by drug treatment in 40 of these patients. As in patients not taking any drug known to inhibit the oxidation of DBQ, distribution of MR values was not different from that in controls. A negative correlation (r = -0.36, p less than 0.02) was found between MR of DBQ and age at onset of disease in patients free of drugs known to interact with DBQ metabolism. A higher rate of DBQ oxidation could be a genetic factor that delays the clinical onset of Parkinson's disease in predisposed people.

Journal Article
TL;DR: In group 16, (78 days of gestation), a decrease in thickness of the muscular layer of all compartments, parallel to the histological differentiation has been observed.
Abstract: Summary. In order to carry out this study, 62 embryos and fetuses of Friesian cows were used, and every stomach was dissected and subjected to the usual laboratory procedures. After obtaining each preparation all the histological and metrical changes that took place in the wall of the viscus during its development are described. The compartments are histologically differentiated into three stages: in the first one there is no compartment differentiation: in the second one, the rumino-reticulum, omasum and abomasum have differentiated; and in the third one every compartment is differentiated. In group 16, (78 days of gestation), a decrease in thickness of the muscular layer of all compartments, parallel to the histological differentiation has been observed.

Journal ArticleDOI
TL;DR: In this paper, the utility of first-derivative fluorimetry for the determination of doxycycline and oxytetracycline through the formation of their chelates with aluminium is discussed.
Abstract: The utility of first-derivative fluorimetry for the determination of doxycycline and oxytetracycline through the formation of their chelates with aluminium, is discussed. Mixtures of these compounds were determined by first-derivative fluorimetry with linear calibration graphs established between 0.2 and 1.4 μgml−1 for doxycycline and between 0.05 and 0.6 μgml−1 for oxytetracycline. The application of the method to the analysis of these compounds in pharmaceutical preparations is described and a statistical evaluation of the experimental results is reported.

Journal ArticleDOI
TL;DR: The ozone absorption rate was always higher than 3 times the maximum ozone absorption in organic-free water (value defined as reaction factor) as discussed by the authors, which indicates that the reactions involved develop in the proximity of the gas-liquid interface and the kinetic regime is fast.

Journal ArticleDOI
TL;DR: In this article, a new spectrophotometric method for simultaneous determination of the isomers salicylaldehyde and 4-hydroxybenzaldehyde is proposed, where binary mixtures are resolved on the basis of the first derivative of the ratio spectra obtained by dividing the amplitude of the salicity spectra by a standard spectrum of 4hydroxy benzaldehyde for (determining salicity) and vice versa for determining 4-hexane.
Abstract: A new spectrophotometric method for simultaneous determination of the isomers salicylaldehyde and 4-hydroxybenzaldehyde is proposed Binary mixtures are resolved on the basis of the first derivative of the ratio spectra obtained by dividing the amplitude the salicylaldehyde absorption spectra by a standard spectrum of 4-hydroxybenzaldehyde for (determining salicylaldehyde) and vice versa for determining 4-hydroxybenzaldehyde - The method compares favorably with other spectrophotometric methods

Journal ArticleDOI
TL;DR: The results reveal a specific distribution of tenascin in the areas of the cono-truncus undergoing significant structural changes during morphogenesis of this cardiac segment, appearing mainly in the mesenchymal layer subjacent to the myocardial layer, the Cono-Truncal ridges and the aorto-pulmonary septum.
Abstract: The cono-truncus constitutes a complex segment of the developing heart that gives rise to the outflow tract of the ventricles and root of the pulmonary and aortic arteries. Numerous studies have revealed that the extracellular matrix plays a relevant role in most morphogenetic processes modulating cell behaviour. By means of immunofluorescence, we studied the distribution and possible involvement of tenascin during morphogenesis of the conus and truncus in chick embryo hearts between days 4.5-10 of incubation. Tenascin is an extracellular matrix glycoprotein with a significant role in morphogenesis and cell and tissue differentiation. Our results reveal a specific distribution of tenascin in the areas of the cono-truncus undergoing significant structural changes during morphogenesis of this cardiac segment, appearing mainly in the mesenchymal layer subjacent to the myocardial layer, the cono-truncal ridges and the aorto-pulmonary septum. The distribution of tenascin was compared and contrasted with that of collagen type I, which constitutes a further component of the extracellular matrix common to most developing connective tissues.

Journal ArticleDOI
TL;DR: M morphological evidence of macrophage-like cells within the suboptic necrotic centres of the chick embryo diencephalon floor and mesenchymal cells with morphological features similar to these cells in the process of traversing the neuroepithelium from the mesenchyme compartment toward the ventricular lumen are reported, suggesting that the intraventricular macrophages arise from the MesenchYme underlying the diencecephalon floor.
Abstract: In the suboptic necrotic centres (SONCs) of the chick embryo diencephalon floor, large numbers of cells die in Hamburger and Hamilton's (HH) developmental stages 14–23. Until recently, it was thought that in these centres, the fragments of dead cells were phagocytosed exclusively by neighboring healthy cells but not by specialized macrophages. We now report morphological evidence of macrophage-like cells within the SONCs of the chick embryo. The distinctive features of these cells are their more or less spherical shape, a nucleus with a thin band of heterochromatin just beneath the nuclear envelope, and cytoplasm showing abundant digestive vacuoles and mitochondria with an electron-lucent matrix. These cells are capable of undergoing mitosis, and selectively stain with the histochemical technique for acid phosphatase. The macrophage-like cells are rare in SONCs in stages HH14-20 and become much more abundant in developmental stages just before the disappearance of these necrotic centres, suggesting that they phagocytose debris from the last cells to die in the SONCs. Acid phosphatase-positive mesenchymal cells with morphological features similar to those of macrophage-like cells are seen in intimate relationship with the basal surface of the SONCs in places where the basal lamina is sometimes missing. These observations suggest that macrophage-like cells in the SONCs arise from the underlying mesenchyme. Free macrophage-like cells with mitotic capacity are also seen in the ventricular lumen adjacent to the apical surface of the diencephalon floor in zones related to the presumptive optic pathways. These cells phagocytose cell debris shed from both the SONCs and from the partially disorganized areas in the neuroepithelium. In these latter we have identified mesenchymal cells with morphological features similar to the macrophage-like cells in the process of traversing the neuroepithelium from the mesenchymal compartment toward the ventricular lumen, thus suggesting that the intraventricular macrophage-like cells arise from the mesenchyme underlying the diencephalon floor.

Journal ArticleDOI
TL;DR: It is concluded that there exists a similar population of adenosine A1 and A2 receptors in chorionic vessels, which mediateAdenosine relaxation, which appears to be mainly produced by inhibition of Ca influx, but not by a cAMP-dependent mechanism.
Abstract: 1. 1. Adenosine induced concentration-dependent relaxations in segments of human chorionic arteries and veins precontracted with 75 mM K+, which were attenuated by l-methyl-3-isobutylxanthine (MIX). In the same conditions, l -phenylisopropyladenosine ( l -PIA), N-ethylcarboxamideadenosine (NECA) and dibutyryl-cyclic AMP (Db-cAMP) also produced concentration-dependent vasodilations. 2. 2. The order of potency with respect to EC50 was in arteries: NECA ⩾ l -PIA > Db-cAM P ⩾ adenosine, and in veins: l -PIA ⩾ NECA > adenosine ⩾ Db-cAMP. 3. 3. In segments precontracted with 10−6 M PGF2α, adenosine, NECA and l -PIA induced similar relaxations, which were markedly larger than those found in K+ contracted segments. 4. 4. Db-cAMP (15 min preincubation) inhibited more potently K+ (75 mM) contractions than adenosine. 5. 5. Adenosine reduced Ca addition-induced contractions in depolarized segments exposed to Ca-free medium, as well as 45Ca uptake elicited by 75 mM K+. 6. 6. It is concluded that there exists a similar population of adenosine A1 and A2 receptors in chorionic vessels, which mediate adenosine relaxation. This effect appears to be mainly produced by inhibition of Ca influx, but not by a cAMP-dependent mechanism.

Journal ArticleDOI
TL;DR: No differences were found in the Michaelis‐Menten constant values for aminopyrine or NADPH, strongly suggesting that interindividual differences could be due to the occurrence of different amounts of the same enzyme, rather than the presence of different enzymes, in the population studied.
Abstract: Aminopyrine N-demethylase activity and the contents of cytochrome P-450, cytochrome b5, and NADPH-reductase activity in human liver microsomes from 31 different patients were studied Our results show the existence of significant interindividual, but not sex- or age-related differences in N-demethylase activity (ranging between 052 and 442 nmol/min/mg protein), and that these differences are directly correlated with the content of cytochrome P-450 and NADPH-reductase activity, but not with that of cytochrome b5 content, in the samples In contrast, no differences were found in the Michaelis-Menten constant values for aminopyrine (mean, 24 mmol/L) or NADPH (mean, 69 mumol/L), strongly suggesting that interindividual differences could be due to the occurrence of different amounts of the same enzyme, rather than the presence of different enzymes, in the population studied

Journal ArticleDOI
01 Jun 1990
TL;DR: In this article, a simple model for the vibrational treatment of diatomic molecules in solution using the basic polarizable continuum method is presented, and the model is extended to the case of the polarizable spectrum.
Abstract: A simple model is presented for the vibrational treatment of diatomic molecules in solution using the basic polarizable continuum method.

Journal ArticleDOI
TL;DR: In this article, an ab initio method for the evaluation of free energy solvation changes near the interface of a solvent system composed of two immiscible liquids is illustrated with the examples of C2H5OH and C 2H5NH2 at the boundary of the water-benzene phase separation.

Journal ArticleDOI
TL;DR: In this paper, a generalized harmonic balance method is used to determine the limit cycles of the generalized van der Pol oscillators X +AX+2BX 3 +ϵ(z 3 +z 2 X 2 +z 1 X 4 ) dot X = 0.

Journal ArticleDOI
TL;DR: The anaerobes most frequently isolated belonged to the following genera: Bacteroides (80%), Peptostreptococcus (63·6%), Megasphaera (40%), Fusobacterium (29·2%), Clostridium (22·5), Propionibacterium(12·5%), Eubacterium and Leptotrichia (10·8%).

Journal ArticleDOI
TL;DR: In this article, le mecanisme proposed for the reaction entre CO 2 and des amines tertiaires is confirmed and verifie la valeur de la constante de vitesse a 25°C and presente de nouvelles donnees pour des temperatures comprises entre 20 and 40°C.
Abstract: On confirme le mecanisme propose pour la reaction entre CO 2 et des amines tertiaires. On verifie la valeur de la constante de vitesse a 25°C et on presente de nouvelles donnees pour des temperatures comprises entre 20 et 40°C.

Journal ArticleDOI
TL;DR: In this paper, isothiocyanates and tri-n -butyltin hydride have been used to produce thioformamides under mild conditions with high yield.

Journal ArticleDOI
TL;DR: The results indicate that protein kinase C activation is associated with pancreatic Juice secretion and it may also modulate secretin-induced pancreatic juice flow in the anaesthetized rat.
Abstract: 1. An investigation was made of the effects of phorbol esters, 12-O-tetradecanoylphorbol acetate (TPA) and secretin on pancreatic juice secretion in the anaesthetized rat. TPA (10(-12)-10(-8) mol/kg body wt) evoked marked dose-dependent increases in secretory rate and total protein output. 2. An inactive phorbol ester (4 alpha-phorbol-12-13-didecanoate; 4 alpha PDD) had no effect on the secretory rate but increased total protein output compared to saline control animals. 3. When TPA was administered in combination with the protein kinase C inhibitor, Polymyxin B (10(-8) mol/kg body wt) both secretory rate and protein output were significantly reduced (P less than 0.001) compared to TPA alone. 4. Secretin (50-1600 pmol/kg body wt) increased both pancreatic juice flow and total protein output in a dose-dependent manner. 5. Simultaneous administration of secretin (50-1600 pmol/kg body wt) and TPA (10(-10) mol/kg body wt) resulted in a marked attenuation in the secretin-induced secretory rate while secretin-evoked protein output was unaffected. 6. The results indicate that protein kinase C activation is associated with pancreatic juice secretion and it may also modulate secretin-induced pancreatic juice flow in the anaesthetized rat.


Journal ArticleDOI
TL;DR: The analytical method is more accurate than the graphical method and is in good agreement with the experimental data obtained by molecular dynamics simulation in the melting zone when a very accurate algorithm is used.