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Biomedical subjects

M Bara

Publications and source records attributed to M Bara.

At least 19 recordsLinked to original sources
PubMed1992

Magnesium and blood pressure. II. Clinical studies.

Magnesium deficit may be considered as a cardiovascular risk because of its aetiopathogenic role in the genesis of atherogenous dyslipidaemias and the so-called "idiopathic" mitral valve prolapse. It does not, however, constitute a major antihypertensive factor, though it may sometimes be an accessory co-factor. Plasma magnesium is generally normal in untreated hypertensive patients and normotension is the rule during magnesium deficit. An inverse relationship between magnesium and renin in the plasma of hypertensives has not been confirmed. In practice, plasma magnesium seems to be related to the evolution of the disease. An inverse correlation between blood pressure and erythrocyte total and free magnesium levels has been observed in diverse selected populations but no adjustment has been made in these studies for important covariables. A weak positive association between blood pressure and erythrocyte free magnesium was lost in a multivariate regression analysis. As a rule there is no difference between erythrocyte, leucocyte, and lymphocyte magnesium in hypertensives and controls. More often no relation between urinary magnesium and blood pressure is observed. Daily urine magnesium may be increased with increased excretion of urine adrenaline. Epidemiological data on dietary magnesium, particularly in drinking water, should be carefully scrutinized: these studies do not establish a major role for magnesium as an antihypertensive factor but confirm the importance of magnesium deficit as a nephrocardiovascular risk factor and sometimes gives support for a role of magnesium as an antihypertensive cofactor. The use of magnesium-depleting drugs in hypertensive patients may induce magnesium depletion which must be palliated.(ABSTRACT TRUNCATED AT 250 WORDS)

Blood Pressure↗
PubMed1992

A new method of in vitro prescreening evaluation of several Mg salts.

The human amniotic membrane may be considered a model for the prescreening evaluation of the membrane effects of several Mg salts because it is an asymmetrical membrane (polarity of the 2 sides: the ratio between the total ionic conductance Gt both ways and the ratio between the ionic flux from the mother to the fetus (F1) and the ionic flux from the fetus to the mother (F2) are different from 1), samples of which can be obtained without ethical problems, and which is easily usable. Whatever the tested salt, the ratio F1/F2 must be constant or increased without alterations of the ionic fluxes (+/-20%), because a toxic metal (As) has no effect on F1/F2, but strongly decreases the ionic fluxes. To apply this model to the study of the effects of Mg salts, two conditions should be considered: 1) Mg oral therapy: Mg deficit increases the membrane fluidity and the increase of Mg concentration rigidifies the membrane, i.e. decreases Gt; the plasma level of Mg being equal to 1 mM, Mg salts would be tested at 1 mM and Gt should be decreased; and 2) Mg parenteral therapy: the Mg effects should be opposite to those of pollutants and alcohol, which reduce Gt; a dose of 3 mM is chosen and Gt should be increased. The general scheme to study Mg salts is the following: observation of the variation of F1/F2 at 1 mM and of the evolution of Gt, and identical observations at 3 mM. This in vitro prescreening method, indirectly applicable to in vivo effects, gives a classification of Mg salts which may be completed by a study of the 10 components of Gt in the case of identical results for Mg salts.

Amnion↗
PubMed1992

A new method of in vitro prescreening evaluation of the relationship between toxic and common metal ions.

The human amniotic membrane, an asymmetrical and nonexcitable epithelium with sites differently situated on the fetal and maternal sides, may be considered a model for investigating the relationship between toxic and common metal ions. The method is based on the observation of the ionic transfer across the amnion, estimated by measuring the total ionic conductance Gt from the mother to the fetus and from the fetus to the mother. It is important to note that opposite effects between two ions are not necessarily correlated with antagonism; indeed, pollutants decrease ionic conductance Gt and Mg increases it, but Mg is not an antagonist of all pollutants. To define antagonism between two ions, the Dixon curves theory should be applied. These curves represent the variation of Gt when the concentration of common metal increases (1 mM, 3 mM), while the concentration of toxic metal is maintained constant (3 concentrations of toxic metal are used). The straight lines obtained are either parallel to each other (noncompetitive inhibition), parallel to the x axis (no interaction between common and toxic metals), or the 3 lines intersect at a common point equal to the inhibition constant. At pharmacological doses, there is competitive inhibition (specific antagonism) between Mg and Cd, Zn and Cd, Ca and Cd, and Mg and Pb, and noncompetitive inhibition between Mg and Hg. This method may rapidly indicate a membrane interaction between common and toxic metals.

Amnion↗
PubMed1991

Prevalence and prediction of hypoxemia in children with respiratory infections in the Peruvian Andes.

To determine the effect of respiratory infections on oxyhemoglobin saturation in a high-altitude population, we recorded clinical signs, oxyhemoglobin saturation determined by pulse oximetry, and findings on radiographs of the chest of 423 children with acute respiratory infections; the children were living at an altitude of 3750 m in the Peruvian Andes. We defined hypoxemia as an oxyhemoglobin saturation value greater than 2 SD below the mean value for 153 well children in this population. Eighty-three percent of children with clinical bronchopneumonia, but only 10% of children with upper respiratory tract infection, had hypoxemia (p less than 0.001). Compared with previous studies of children living at lower altitudes, the presence of tachypnea was relatively nonspecific as a predictor of radiographically determined pneumonia or of hypoxemia, especially in infants. A history of rapid breathing was 74% sensitive and 64% specific in the prediction of hypoxemia, and performed as well as a standard World Health Organization case management algorithm in the prediction of radiographic pneumonia or hypoxemia. Radiographic pneumonia was not a sensitive predictor of hypoxemia or clinically severe illness. In contrast, the presence of hypoxemia was a useful predictor of radiographic pneumonia, with both sensitivity and specificity of 75% in infants. We conclude that acute lower respiratory tract infection in children living at high altitude is frequently associated with hypoxemia, and that oxygen should be administered to children with a diagnosis of pneumonia in these regions. Case management algorithms developed in low-altitude regions may have to be modified for high-altitude settings. In this setting, pulse oximetry is a good predictor of pneumonia. Because pulse oximetry is more objective and cheaper than radiography, its role as a clinical and investigative tool merits further exploration.

Acute Disease↗
PubMed1991

Comparative study of effects of magnesium and taurine on electrical parameters of natural and artificial membranes. VIII. Effect on the ultrastructure of human amniotic epithelial cells.

The ultrastructure of human amniotic epithelial cells from normal pregnancies, at term, was studied using transmission electron microscopy. The results were analysed by a stereological method which indicates the ratio between the volume of the intercellular space (R1, the microvilli (R2), and the podocytes (R3) versus the cell volume. At low concentration (2 mM), MgCl2 decreased R1 and R3 and had no significant effect on R2. In contrast, taurine (2 mM) increased R1 and had no significant effect on R2 and R3. There is no vicarious action between Mg and taurine. These data are in contrast to the results obtained after electrophysiological studies, which indicates that the structural targets for Mg and taurine are different from the targets responsible for ionic transfer.

Amnion↗
PubMed1991

Toxic metals and human amniotic ion permeability. II. Ultrastructural study and relationship with magnesium.

Measurement of the ratio between the volume of the intercellular space (R1), the microvilli (R2), the podocytes (R3), and the nucleus (R4) versus the cell volume indicates the effects of lead (Pb), cadmium (Cd), arsenic (As), and mercury (Hg) on the ultrastructure of the human epithelial cells. R1 is decreased by all toxic metals except Pb. R2 is increased by Cd and As, and decreased by Pb. R3 is not affected. R4 is increased only by As. The addition of MgCl2 to the bathing medium antagonizes the effect of Cd on the intercellular space, of Pb on the microvilli, and of As on nucleus. On the other hand, Mg enhances the effects of Pb on R1 and those of Cd and As on R2. Mg may be either a competitive inhibitor or an activator of the effects of the toxic substances examined in relation to their storage sites.

Amnion↗
PubMed1990

Comparative study of effects of magnesium and taurine on electrical parameters of natural and artificial membranes. VII. Effects on cellular and paracellular ionic transfer through isolated human amnion.

The comparative effects of 2 mM magnesium and taurine on various components of the human transamniotic conductance, Gt, were observed. The use of both microelectrodes and metabolic inhibitors enables 10 components of Gt to be distinguished: six cellular components (Na-K ATPase, Na-H antiport, Na-K-2Cl cotransport and Na, K, Cl channels), one coupling component, and three paracellular components (Na, K, Cl). Mg increased all components of Gt while taurine only increased five of them (Na and K channels, coupling, Na and K paracellular conductance). A potentiometric effect of taurine on Mg2+ modified membrane, obtained on paracellular components, was not measured on cellular components. There was only a vicarious effect between Mg and taurine on the non-enzymatic cellular and paracellular transfer of Na and K.

Amnion↗
PubMed1990

Modification of the human transamniotic ionic transfer after addition of anti-cancer metals.

The effects of anticancer metals (Ga, Cis-Pt, Se) on the ionic transfer through the isolated human amnion, expressed as the measure of the transamniotic conductance Gt, the ionic fluxes and the flux ratio (mother-fetus/fetus-mother: F1/F2) were studied. The 3 metals decrease Gt on the maternal side by a screening effect and have a little effect on the fetal side. The ionic fluxes are decreased on the maternal and on the fetal sides. The flux ratio is reduced by Cis-Pt but becomes constant with Ga and Se. The action of the anticancer metals is identical to the action of the carcinogenic metals on the transamniotic transfer and the membrane does not seem to be the target of the anticancerous action.

Amnion↗
PubMed1990

Ultrastructural effects of magnesium on human amniotic epithelial cells.

The ultrastructure of the human amniotic epithelial cells from normal pregnancies, at term, was studied using scanning and transmission electron microscopy. The results were analysed by a stereological method which indicates the ratio between the volume of the intercellular space (R1), the microvilli (R2), and the podocytes (R3) versus the cell volume. An increase in this ratio indicates a higher structure and a facilitation of ion transport through the membrane. At low concentration (2 mM), MgSO4 increased R1 and R2 but decreased R3, whereas MgCl2 decreased R1 and R3 and had no significant effect on R2. At high concentration (10 mM), MgCl2 decreased R1 and increased R2 and R3, while MgSO4 had no significant effect on R1, increased R2, and decreased R3. The results are in part consistent with the results obtained after electrophysiological studies.

Amnion↗
PubMed1990

Magnesium: a competitive inhibitor of lead and cadmium. Ultrastructural studies of the human amniotic epithelial cell.

The measure of the ratio between the volume of intercellular space (R1), the microvilli (R2), and the podocytes (R3) versus the cell volume indicates the effect of lead (Pb) and cadmium (Cd) on the ultrastructure of the human amniotic epithelial cell. Cd decreased R1 significantly, increased R2 and had no effect on R3. Pb had no effect on R1 or R3 but decreased R2 significantly. The addition of Mg chloride to the bathing medium antagonized the effect of Cd on the intercellular spaces and podocytes. The antagonistic effect of Mg on Pb was observed only on microvilli. These results are consistent with the data obtained with electrophysiological studies which show that Mg is a competitive inhibitor of Pb and Cd.

Amnion↗
PubMed1989

[Late sequelae of epidemic viral meningitis].

In autumn 1982 during an epidemic of meningitis caused by Coxsackie A9 and ECHO4 viruses 36 patients, usually young, were hospitalized. After 3-4 years 22 of them were subjected to control examinations, carrying out medical examination. EEG, ACG, motor nerve conduction velocity measurements and psychological examinations by the tests od Eysenck, Bender-Koppitz and Wechsler. The studied group comprised 14 men and 8 women with mean age 29.8 years.

Adolescent↗
PubMed1989

A qualitative theory of the screening-binding effects of magnesium salts on epithelial cell membranes: a new hypothesis.

A theoretical explanation is given of the screening-binding effects of various magnesium salts on the ionic permeability of epithelial amniotic cell membranes. It is suggested that the 'screening process' induces an increase in the electrical membrane resistance and in membrane stability which is a unique action at low concentration. At high concentration, the binding process induces a reduction or an increase in these parameters as a function of the magnesium salt present. The different effects are due to changes in the distribution and in the repartition of the fixed charges on the cell membrane.

Amnion↗
PubMed1988

Study of the antagonism between zinc and various embryonic toxics on human amnion permeability. I. Zinc and cadmium.

The effects of Cd and Zn have been studied on the ionic permeation of the isolated human amnion, expressed by the measure of the transamniotic conductance Gt and the flux ratio (mother-fetus/fetus-mother: F1/F2). Cd has no action on Gt on the fetal side and decreases Gt on the maternal side by a screening effect. Zn acts on the two faces by a screening-binding effect. The ratio F1/F2 remains constant with Zn concentration, but decreases with Cd and becomes less than 1 at 5 mmol/l of Cd. F1/F2 decreases with the duration of the administration of Cd. Zn has the opposite effect of Cd on the ionic transfer and has a stabilizing action on the amnion. Moreover, Zn may antagonize the noxious effect of Cd on the maternal side.

Amnion↗
PubMed1988

Modification of human amniotic membrane stability after addition of magnesium salts.

Membrane stability is determined by the measure of two electrical parameters: the total ionic conductance (Gt) and the ionic fluxes (F1, F2). These two categories of interaction between the membrane polar groups and magnesium explain its effects on membrane stability. The screening interaction is characterized by the fact that the polar groups are masked by magnesium and by a decrease of Gt, F1 and F2. The membrane stability increases. The binding interaction is characterized by the fact that the polar groups are accessible to other ions and by an increase of Gt, F1 and F2. The membrane stability decreases. Among the different magnesium salts studied, MgCl2, Mg acetate and Mg citrate increase then decrease the stability on the two faces of the amnion. MgSO4, Mg lactate and Mg nitrate increase the stability on the maternal side, but decrease it on the fetal side. MgCl2, Mg acetate and Mg citrate have an identical effect on the two faces of the amnion which does not influence the transfer ratio.

Amnion↗
PubMed1988

Analysis of magnesium membraneous effects: binding and screening.

There are two categories of electrostatic interactions between cations and negatively membrane charged surfaces. First, there is the usual type of electrostatic binding where the cations complex to anionic surface moieties. There exists, however, a second type of association, often referred to as screening. In this case, the cations remain mobile, being held loosely in a diffuse layer close to the surface. When divalent cations are added in the bathing medium, a screening effect (S) induces a reduction of Gt, a binding effect (B) induces an increase of Gt and a screening-binding effect (S-B) induces a reduction, then an increase, of Gt. In the isolated human amnion, among the magnesium salts studied, only MgCl2, Mg citrate and Mg acetate have a S-B effect on both faces of the membrane.

Amnion↗
PubMed1988

The magnesium, calcium, sodium, potassium and chloride contents of the term human placenta.

The ion content of the human term placenta was determined. When ordered decreasingly according to their placental content, the series of ions was: Na greater than Cl greater than K greater than Ca greater than Mg. These levels, plotted as a function of the tissue dry weight, showed an exponential distribution. Using Cl as an extracellular marker, Na and K cellular concentrations were evaluated. The equilibrium potentials derived from these values were very different from the measured syncytial membrane potential or from the value usually recorded in non-innervated tissues.

Calcium↗
PubMed1988

Relationship between magnesium, carcinogenic metals and ionic permeability of the human amnion.

The effects of the well established carcinogenic metals or metalloids (As, Be, Cr, Ni), hypothetically carcinogenic but well-established cocarcinogenic metals (Cd, Pb, Co) and weak co-carcinogenic metals (Al, Cu, Fe, Zn) and the antagonism between Mg and these metals were studied on the ionic transfer through the isolated human amnion. The ionic transfer is estimated by the measure of the membrane potential (delta psi), the cationic number transference t+ and the ionic fluxes (F1, F2). All carcinogenic metals increase delta psi (+) and reduce t+, F1 and F2. Mg has an opposite action with regard to Cd, Pb and Ni, but may act as a co-carcinogenic agent by increasing the effects of Al, Cu and Zn.

Aluminum↗