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Biomedical subjects

A Lopez

Publications and source records attributed to A Lopez.

At least 217 records · Page 12Linked to original sources
PubMed1990

Chief complaint of fatigue: a prospective study.

The Dartmouth COOP Project, a primary care research network, conducted a prospective study of patients presenting to 28 primary care practices with a chief complaint of fatigue. Data were gathered on fatigue status, associated systems, health status, and origin of fatigue. Fatigue patients were demographically similar to nonfatigue patients but had significantly worse physical and mental health at study intake. Sixty-three percent of physicians and 52% of patients rated fatigue origin as primarily physical (gamma = 0.48, P less than .05), but in 41% of cases, physicians indicated there was substantial interaction between physical and psychological factors. Only two factors--depression and anxiety--separated fatigue of physical origin from fatigue of psychological origin. Clinicians must thoughtfully evaluate fatigue's often multiple causes and communicate their understanding of those causes to the patient to gain support for a reasonable treatment regimen.

Adult↗
PubMed1990

Determination of methyl bromide traces in some food products by HS-GC/MS.

A simple and rapid method has been developed for fast selective determination of residues of methyl bromide in food products. The method is based on the use of a GC/MS computer-aided system equipped with a headspace. Analysis of methyl bromide was carried out directly on the food products without preliminary extraction of fumigant. An MSD quadrupole mass spectrometer with data processing allowed rapid identification of the separated volatile compound in the samples. The technique of focusing on characteristic single ion monitoring for quantification of methyl bromide, compared with chromatographic peak area measurement, turned out to have a good degree of accuracy and sensitivity. The use of known amount of added methyl bromide allowed better evaluation of traces of this compound. The proposed method was applied to the analysis of methyl bromide residues in alimentary pastes, white flour, rice, hazelnuts, peanuts and dried mushrooms (boletus).

Food Analysis↗
PubMed1989

Lipid lateral diffusion and membrane organization.

It is shown that investigating the lateral motion of lipids in biological membranes can provide useful information on membrane lateral organization. After labeling membranes with extrinsic or intrinsic lipophilic fluorescent probes, fluorescence recovery after photobleaching experiments strongly suggests that specialized cells like spermatozoa, eggs and epithelia exhibit surface membrane regionalization or macrocompartmentation and that lateral microheterogeneities or lipid microdomains exist in the plasma membrane of many cellular systems.

Animals↗
PubMed1989

Transverse and lateral distribution of phospholipids and glycolipids in the membrane of the bacterium Micrococcus luteus.

The photodimerization of anthracene was used to investigate the transverse and lateral distribution of lipids in the membrane of the Gram-positive bacterium Micrococcus luteus. 9-(2-Anthryl)nonanoic acid (9-AN) is incorporated at a high rate into various membrane lipids of M. luteus. On irradiation of intact bacteria at 360 nm, anthracene-labeled lipids form stable photodimers which can be extracted and separated by thin-layer chromatography. We present here the results of a study on the distribution of two major lipids, phosphatidylglycerol (PG) and dimannosyldiacylglycerol (DMDG), within each leaflet of the membrane lipid bilayer. After metabolic incorporation of a tritiated derivative of 9-AN in M. luteus, the radioactivity associated with the photodimers issued from PG and DMDG was counted. In the bacterial membrane, the ratio of PG-DMDG heterodimer with respect to PG-PG and DMDG-DMDG homodimers is around half of what should be obtained for a homogeneous mixture of the two lipids. In order to find out whether this was due to an asymmetric distribution of the two lipids between the two membrane leaflets or a heterogeneous distribution of the two lipids within the same membrane leaflet, the transverse distribution of PG and DMDG was also investigated. This was carried out by following the kinetics of oxidation of the two lipids by periodic acid in the membrane of M. luteus protoplasts. PG predominated slightly in the outer layer (60%), while DMDG was found to be symmetrically distributed between the two leaflets. By itself, this lipid asymmetry cannot account for the lipid distribution determined from the photodimerization experiments. This indicates that PG and DMDG are not homogeneously distributed in the plane of the bacterial membrane.

Anthracenes↗
PubMed1989

The lateral motion of lipid molecules in the apical plasma membrane of endothelial cells is reversibly affected by the presence of cell junctions.

As with other epithelia, the question arises of whether the endothelial cell junctions participate in cell polarization, restrict the localization of lipid molecules, and lead to differences in their lateral motion between the apical and basolateral plasma membranes. We found that in bovine aortic endothelium in culture, the localization of the lipophilic probe 5N-(hexadecanoyl)-aminofluorescein (HEDAF) was markedly affected by the presence of cell junctions. At confluence, the probe was observed to be restricted to the exoplasmic leaflet of the apical plasmalemma. It was detected in the basal membrane only after disruption of the cell junctions, whereas the cells remained firmly bound to the underlying extracellular matrix. Fluorescence recovery after photobleaching (FRAP) experiments indicated that the endothelial confluent cell monolayer forms a mosaic of closed diffusion areas in which the probe molecules are free to diffuse. For the first time, and using a new mathematical approach, it was possible to estimate the diameter of these diffusion areas. Values in the range 14-33 microns were found which correlate well with the actual measured diameters of 14 to 26 microns for the apical pole of individual cells. Moreover, cell junctions were found to affect the dynamics of the probe. When the cell junctions were disrupted, the lateral diffusion coefficient D of HEDAF was found to be the same in both apical and basal membranes. It regained its initial higher value in the apical poles when cell contacts were restored. This strongly suggests that in vascular endothelium, cell junctions affect overall plasma membrane organization in a reversible manner.

Animals↗
PubMed1989

Effect of cell substratum on lateral mobility of lipids in the plasma membrane of vascular endothelial cells.

Bovine vascular endothelial cells can be maintained in a highly differentiated state in vitro, either by the addition of fibroblast growth factor (FGF) to the culture medium or by plating the cells on extracellular matrix (ECM)-coated dishes. Under these conditions the cells proliferate actively and at confluence form a tightly packed monolayer composed of nonoverlapping polarized cells. A fluorescence recovery after photobleaching method was used to determine the lateral mobility coefficient D of the lipophilic fluorescent probe, 5N-(hexadecanoyl)-aminofluorescein (HEDAF), in the basal and apical plasma membranes of endothelial cells under various culture conditions (cells on glass coverslips in the presence or absence of FGF, or cells plated on ECM in the exponential growth phase or at confluence). A heterogeneous distribution of lateral diffusion coefficients D was found in a given cell population. Nevertheless, for the basal membrane, a "mean" D value close to 2.0 x 10(-9) cm2/s was found for all the culture conditions. The "mean" D value of HEDAF in the apical pole was slightly higher when sparse cells were exposed to FGF (D = 2.2 x 10(-9) cm2/s) and was further enhanced when cells were growing or confluent on ECM-coated coverslips (D = 2.7 x 10(-9) cm2/s). On the other hand, when the cells were maintained in the absence of FGF on glass coverslips, similar "mean" D values were found in both cell poles (D = 2.0 x 10(-9) cm2/s). These results show that lateral mobility of lipids in endothelial plasmalemma varies in response to external factors such as FGF and the ECM.

Animals↗
PubMed1989

Peracute toxic effects of inhaled hydrogen sulfide and injected sodium hydrosulfide on the lungs of rats.

This study was designed to test whether intraperitoneally injected sodium hydrosulfide (NaHS) would mimic the pulmonary alterations induced by lethal peracute exposure to an atmosphere containing hydrogen sulfide. Groups of five Sprague-Dawley rats were exposed to an atmosphere of either 2317.6 +/- 547.3 mg m-3 H2S (H2S group) or no H2S (air group), or were injected intraperitoneally with a solution containing 30 mg kg-1 sodium hydrosulfide (NaHS group) or saline solution (vehicle control). Rats of the air and saline groups were killed by cervical dislocation. All rats exposed to H2S or injected with NaHS died within 3 min; however, only rats exposed to H2S showed severe respiratory distress in the agonic phase preceding death. In addition, rats in the H2S group had a notable discharge of serous fluid from the mouth and nostrils. At necropsy, all rats in the H2S group had gross and histologic evidence of pulmonary edema characterized by massive extravasation of eosinophilic fluid into the bronchoalveolar space. In contrast, the lungs of rats injected with NaHS or saline or exposed to air were unaffected. It was concluded that the edematogenic effect of H2S in the lungs cannot be reproduced by injection of NaHS. The severity of lung edema induced by a peracute exposure to H2S was extensive enough to account for death.

Administration, Inhalation↗
PubMed1989

Continuous fluorescence microphotolysis of anthracene-labeled phospholipids in membranes. Theoretical approach of the simultaneous determination of their photodimerization and lateral diffusion rates.

Anthracene is a fluorescent and photoactivatable (dimerization) group which can be used for investigating the lateral distribution and dynamics of lipids in membranes. In fluorescence recovery after photobleaching or in microphotolysis experiments, and when using this fluorophore, the bleaching (or microphotolysis) step in the illuminated part of the membrane is in fact the sum of two antagonistic processes: fluorescence decay, which is due to dimerization of anthracene residues, and fluorescence recovery, which is due to a diffusion mediated exchange of bleached and unbleached particles between the illuminated and diffusion area in the membrane. Here, we propose a new mathematical algorithm that enables such a second-order reaction-diffusion process to be analyzed. After coupling a fluorescence recovery step to a microphotolysis step, this algorithm allows us to calculate the lateral diffusion coefficient D and the photodimerization constant K of anthracene-labeled lipids in membranes, two parameters which contribute to the understanding of the fluidity of the lipid phase in membranes. This algorithm also provides us with a complete description of the anthracene-labeled molecules distribution in the illuminated and diffusion area, at any time of the experiment. The fluorescence recovery after microphotolysis procedure we propose was tested with an anthracene-labeled phosphatidylcholine inserted in egg-phosphatidylcholine multilayers, in monolayers adsorbed onto alkylated glass surfaces and in the plasma membrane of Chinese hamster ovary cells. It is shown that this procedure can also be used to evaluate the important parameters of probe mobile fraction and to determine the relative size of the illuminated and diffusion areas. This will enable membranes to be explored in terms of microdomains and/or macrodomains.

Algorithms↗
PubMed1989

Ionic and energetic changes at competence in the naturally transformable bacterium Streptococcus pneumoniae.

Addition of competence factor extracts to trigger competence in a culture of Streptococcus pneumoniae induced an increase in the intracellular pH and the Na+ content of the bacteria without any change in the K+ pool or in the membrane potential. These ionic shifts were concomitant with a stimulation of glycolysis that resulted in an enhanced ATP pool. Thus, in transforming conditions, at extracellular pH 7.8, competent bacteria presented a particularly high energetic state resulting from an increase in delta pH and in the ATP pool, associated with an enhanced Na+ content. These features are discussed in the context of homeostasis regulation in response to an environmental stimulus.

Adenosine Triphosphate↗
PubMed1988

31P NMR analysis of membrane phospholipid organization in viable, reversibly electropermeabilized Chinese hamster ovary cells.

Chinese hamster ovary (CHO) cells were reversibly permeabilized by submitting them to short, high-intensity, square wave pulses (1.8 kV/cm, 100 microseconds). The cells remained in a permeable state without loss of viability for several hours at 4 degrees C. A new anisotropic peak with respect to control cells was observed on 31 P NMR spectroscopic analysis of the phospholipid components. This peak is only present when the cells are permeable, and normal anisotropy is recovered after resealing. Taking into account the fusogenicity of electropermeabilized cells, comparative studies were performed on 5% poly(ethylene glycol) treated cells. The 31P NMR spectra of the phospholipids displayed the same anisotropic peak as in the case of the electropermeabilized cells. In the two cases, this anisotropic peak was located downfield from the main peak associated to the phospholipids when organized in bilayers. The localization of this anisotropic peak is very different from the one of a hexagonal phase. We proposed a reorganization of the polar head group region leading to a weakening of the hydration layer to account for these observations. This was also thought to explain the electric field induced fusogenicity of these cells.

Animals↗
PubMed1988

Comparative study of the lateral motion of extrinsic probes and anthracene-labelled constitutive phospholipids in the plasma membrane of Chinese hamster ovary cells.

9-(2-Anthryl)-nonanoic acid is a new photoactivatable fluorescent probe which has been designed for the study of the lateral diffusion and distribution of lipids in biological membranes by means of the anthracene photodimerization reaction. This anthracene fatty acid can be incorporated metabolically into the glycerophospholipids (phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine, phosphatidylinositol) of Chinese hamster ovary (CHO) cells in culture. The diffusion coefficient of intrinsic lipids in the plasma membrane of these eukaryotic cells can thus be measured using the fluorescence recovery after a photobleaching technique, since illumination of the fluorescent anthracene groups yields non-fluorescent photodimers. For the sake of comparison, the extrinsic lipophilic probes 5-(N-hexadecanoyl)-aminofluorescein, 12-(9-anthroyloxy)-stearic acid, 9-(2-anthryl)-nonanoic acid and a synthetic anthracene-phosphatidylcholine were also used to label the plasma membrane of CHO cells. The diffusion coefficients for the extrinsic and intrinsic probes ranged over 1 - 2 x 10(-9) cm2/s. Small but significant differences were observed between the various probes reflecting differences they exhibit in size and polarity. All the extrinsic probes were free to diffuse, with a mobile fraction close to 100%. In contrast, a fractional recovery of only 75% was observed for the intrinsic anthracene-labelled phospholipids, suggesting that the anthracene fatty acid was metabolically incorporated into membrane lipid regions which were inaccessible to the extrinsic probes.

Affinity Labels↗
PubMed1988

The quality and extension of nerve fibre regeneration in the centrocentral anastomosis of the peripheral nerve.

Centro central anastomosis (CCA) is the connection created by means of a nerve autograft placed between the fascicles of the proximal stump of a sectioned nerve. We have used this technique in the laboratory and in the human to avoid the formation of a terminal neuroma after amputation of a limb. The aim of the present study is to know what is the quality and how long is the progression of the regenerating nerve fibers coming from a fascicle and growing inside the nerve graft and into the other central fascicle. 56 male, adult, Sprague-Dawley rats were operated on. The 4 rats of Group I were used for control: the right sciatic nerve was exposed and dissected in its four branches. One piece of 10 mm was taken of each of the sural and the peroneal branches for hystological and histomorphometric studies. In the 16 rats of Group II, after the section of the sural and peroneal branches a terminoterminal suture between their proximal stumps was made. In the 16 rats of Group III a CCA with an interposed nerve graft of 7 mm was achieved. 5.5 and 6 rats of Groups II and III were sacrificed at 10, 40 and 365 days after the operation and the entire graft was taken for histological analysis. In the 20 rats of Group IV, 60 days after CCA, the graft was sectioned at its center to produce wallerian degeneration of nerve fibers. 10 days after this second operation the animals were sacrificed and the nerve specimens were taken for histological study.(ABSTRACT TRUNCATED AT 250 WORDS)

Anastomosis, Surgical↗
PubMed1988

Evidence for hydroxyl free radical formation during paraquat but not for nifurtimox liver microsomal biotransformation. A dimethyl-sulfoxide scavenging study.

The effect of several experimental conditions on methane (CH4) production from dimethylsulfoxide (DMSO) in incubation mixtures containing liver microsomes and NADPH generating systems was studied. The process was heat sensitive in part but a significant fraction was non-enzymatic in nature. CH4 formation from DMSO was not significantly modified by 2-diethylaminoethyl-2,2-diphenylvalerate. HC 1 (SKF 525A) or EDTA 1 mM and significantly enhanced under an atmosphere of (CO 80% + O2 20%) rather than under air. A marked increase in CH4 production was observed when paraquat (PQ) was included in incubation mixtures but not when nifurtimox (Nfx) was added. Results support the hypothesis of hydroxyl free radical (.OH) formation during PQ biotransformation but cast doubts about its production for the case of Nfx. The low temperature gas chromatographic separation of d3-CH4 from CH4 described opens the future possibility for detecting trace formation of .OH in vivo, without interference from fecal CH4 formation by administering d6-DMSO to animals and collecting exhaled gases produced, in chambers containing the entire animal.

Animals↗