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Biomedical subjects

A Robert

Publications and source records attributed to A Robert.

At least 199 records · Page 11Linked to original sources
PubMed1994

Uptake of potassium by nonmyelinating Schwann cells induced by axonal activity.

1. The electrophysiological properties of the rabbit vagus nerve (membrane potential, compound action potentials, and afterpotentials) and potassium accumulation were measured simultaneously during low-frequency stimulation (LFS) (0.5 and 1 Hz) by using a modified sucrose-gap apparatus and potassium-sensitive microelectrodes (KSM). 2. During LFS at 0.5 and 1 Hz, the concentration of K+ in the extracellular space ([K+]c) increased in approximately 30 s to a maximal level that was 0.6 and 1.5 mM, respectively, above the resting concentration. Concomitantly the preparation developed an ouabain-sensitive hyperpolarization. 3. The compound action potential (CAP) was followed by a fast hyperpolarizing afterpotential (fHAP), a depolarizing afterpotential (DAP), and a slow hyperpolarizing afterpotential (sHAP). During LFS the characteristics of all these afterpotentials were profoundly modified. In parallel to the increase in [K+]e, the fHAP was decreased and the amplitude of the DAP was dramatically enhanced. Furthermore, the sHAP which had a duration of < 1 s when it followed a single CAP, turned into a ouabain-sensitive hyperpolarization (indicating that it was generated by the electrogenic Na(+)-K+ pump) that lasted several minutes. 4. The application of external Ba2+ produced a hyperpolarizing sag on the sHAP following a single isolated CAP. During LFS, Ba2+ enhanced the build-up of the DAP, raised the maximal level of [K+]e, and increased the activity-induced ouabain-sensitive hyperpolarization. 5. The increase by Ba2+ of the activity-induced hyperpolarization shifted the spikes from both myelinated and nonmyelinated fibers toward a more negative potential but did not increase their amplitude, indicating that this Ba(2+)-induced hyperpolarization originated from an extra-axonal source, presumably the Schwann cells. 6. It is proposed that the electrogenic activity of the Na(+)-K+ pump was enhanced in Schwann cells situated near active axons. This hyperpolarization was, however, not recorded in normal conditions because it was fully short-circuited by a K+ influx through Ba(2+)-sensitive channels. 7. Our results lead to the hypothesis that the Na(+)-K+ pump of the nonmyelinating Schwann cells is important in the mechanisms maintaining the homeostasis of K+ in the axonal microenvironment. They show that the Na(+)-K+ pump contributes to the K+ buffering not only by actively pumping K+ but also by generating a hyperpolarization that drives a passive K+ influx through Ba(2+)-sensitive K+ channels.

Action Potentials↗
PubMed1994

Utrophin localization in normal and dystrophin-deficient heart.

BACKGROUND: The localization of dystrophin at the sarcolemma of cardiac skeletal fibers and cardiac Purkinje fibers has been described. Dystrophin deficiency produces clinical manifestations of disease in skeletal muscles and hearts of patients with Duchenne and Becker muscular dystrophy. Utrophin (or dystrophin-related protein), a dystrophin homologous protein, was found to be expressed in fetal muscles and reexpressed in dystrophin-deficient skeletal muscle fibers. We therefore examined utrophin expression in normal and in dystrophin-deficient hearts. METHODS AND RESULTS: The expression and subcellular distribution of utrophin was examined in cardiac muscle by immunoblot and immunofluorescence analysis in normal bovine heart compared with dystrophin. Utrophin expression was also examined in normal and dystrophin-deficient hearts of MDX mice. Three monoclonal antibodies reacting with dystrophin and utrophin solely or reacting with both proteins along with two polyclonal antibodies reacting with either utrophin or dystrophin and utrophin were tested. In normal bovine heart, utrophin was not expressed at the periphery of fibers but was strongly expressed in intercalated disks and in the cytoplasm of cardiac Purkinje fibers. In cardiocytes, utrophin was colocalized along transverse T tubules with dystrophin. Dystrophin was present at the periphery of cardiocytes and cardiac Purkinje fibers as well as in transverse T tubules but was absent or faintly expressed in intercalated disks. The results with monoclonal and polyclonal antibodies were identical. Western blot analysis revealed that the detected molecules corresponded only to a 400-kD protein band and not to possible shorter transcripts of utrophin or dystrophin (apo-utrophin or apo-dystrophin). In dystrophin-deficient hearts of MDX mice, utrophin alone was abundant but not organized in the same networklike distribution. CONCLUSIONS: This first localization of utrophin in normal heart (in Purkinje fibers, transverse tubules, and intercalated disks) showed a distinct subcellular localization of this protein with dystrophin, suggesting an important function of this protein in intercellular communication. In dystrophin-deficient hearts of MDX mice, utrophin alone is overexpressed as in skeletal muscle sarcolemma, an area normally occupied by dystrophin but not organized in the same networklike distribution.

Animals↗
PubMed1994

Intensified conditioning regimen with busulfan followed by allogeneic BMT in children with myelodysplastic syndromes.

Four consecutive children with myelodysplastic syndromes (MDS) underwent matched allogeneic bone marrow transplantation (BMT). Ages ranged from 3.2 to 6.3 years. Diagnosis was assessed according to FAB classification: refractory anemia-RA (n = 1), RA with excess of blasts (RAEB) (n = 1), and juvenile chronic myelogenous leukemia (JCML) (n = 2). Initial treatment included transfusions for all of them, splenectomy (n = 2) and chemotherapy (n = 1). Patients were all prepared with busulfan 21 mg/kg (480 mg/m2), cytosine arabinoside 24,000 mg/m2, melphalan 140 mg/m2. Graft-versus-host disease (GVHD) prophylaxis associated cyclosporine-methotrexate. Engraftment was prompt and complete in all children. Toxicity included severe mucositis (n = 3), moderate veno-occlusive disease (n = 2), acute GVHD (n = 3), chronic GVHD (n = 1). Sequelae have not yet been seen. All patients are alive and disease-free with a follow-up ranging from 7 to 35 months, with a Karnofsky score of 90-100%. Combined busulphan conditioning can offer an alternative to total body irradiation-based regimens in order to avoid late side-effects in children.

Anemia, Refractory↗
PubMed1994

Differences in vasoreactivity between gastroepiploic artery grafts late after bypass surgery and grafted coronary arteries.

BACKGROUND: The gastroepiploic artery is increasingly used as an alternative arterial coronary bypass conduit. In vitro studies have reported differences in vasoreactivity among various types of coronary graft conduits, susceptible to influencing the adaptation of myocardial blood flow and long-term patency rate. METHODS AND RESULTS: To evaluate in vivo the vasoreactivity of gastroepiploic artery grafts implanted long-term, nine angiographically smooth grafts implanted to the distal right or to the left circumflex coronary artery were studied with quantitative angiography 6 to 36 months after surgery. Angiograms were obtained on 35mm cinefilms in basal conditions, after injection of methylergometrine (0.4 mg IV), and after intragraft injection of 1 mg isosorbide dinitrate. In basal conditions, there was no difference in luminal diameter between gastroepiploic and coronary arteries (1.64 +/- 0.32 versus 1.51 +/- 0.31 mm; P = NS). After methylergometrine, a constriction was observed in all gastroepiploic artery grafts (-14 +/- 6% of basal diameter) and in all but one grafted coronary artery (-6 +/- 5%). After isosorbide dinitrate, a dilation was consistently observed in all gastroepiploic artery grafts (+26 +/- 9%) and grafted coronary arteries (+14 +/- 7% of basal). Changes in lumen diameter in response to these constrictor and dilator stimuli, either expressed in absolute values or in percentage of control were significantly greater (P < .001) in gastroepiploic artery grafts than in grafted coronary arteries. CONCLUSIONS: Gastroepiploic artery grafts implanted long-term are more reactive than grafted coronary arteries to ergometrine and nitrates. This response differs from that previously reported of internal mammary artery grafts to the same pharmacological vasoactive stimuli. This suggests that the concept of a more efficient endothelium-dependent control of vasomotor tone contributing to better long-term functional results of internal mammary artery grafts cannot be directly extrapolated to gastroepiploic artery grafts.

Arteries↗
PubMed1994

[Acute hepatopathy compatible with Reye's syndrome in 3 children treated by chemotherapy].

BACKGROUND: Chemotherapy for malignant diseases sometimes leads to hepatic toxicity. Reye's syndrome has not been described in such a situation. CASE REPORTS: Three children, 4, 5 and 6 years-old, were treated for lymphoma or acute lymphoblastic leukemia. They were given polychemotherapy including drugs that were not potentially hepatotoxic. During remission, they suddenly developed manifestations such as neurologic disturbances, hepatomegaly, increased activity of liver enzymes, and microvesicular steatosis. These disturbances were consistent with the diagnostic criteria for Reye's syndrome recommended by the Centers for Disease Control. Factors such as viral infection, salicylate administration, primary metabolic disorder were not present. One child died and the other two recovered completely. CONCLUSION: Patients given chemotherapy, even though the relationship between them remains to be determined, may develop manifestations compatible with a diagnosis of Reye's syndrome.

Antineoplastic Combined Chemotherapy Protocols↗
PubMed1994

Inhibition of procoagulant activity of human monocytes by chenodeoxycholic acid: involvement of protein kinase C.

Endogenous bile acids such as chenodeoxycholic acid have been shown to display a suppressive effect in vitro on mononuclear cell activation. We investigated the signal transduction pathway involved in the effect of chenodeoxycholic acid on monocyte procoagulant activity, a model of monocyte activation. Chenodeoxycholic acid (25 to 250 mumol/L) had a concentration-dependent inhibitory effect on procoagulant activity expressed by endotoxin-stimulated mononuclear cells, with half-maximal and maximal inhibition occurring at concentrations of 100 and 250 mumol/L, respectively. The inhibitory effect of chenodeoxycholic acid was (a) closely mimicked by 4 beta-phorbol 12 beta-myristate 13 alpha-acetate (PMA), a protein kinase C activator, but not by forskolin or dibutyryl cyclic AMP, two activators of the protein kinase A-dependent pathway; (b) prevented by staurosporine, a potent protein kinase C inhibitor; (c) partially abolished in protein kinase C-depleted cells; and (d) observed in conditions under which chenodeoxycholic acid, like PMA, significantly increased (41%) protein kinase C activity, as assessed by phosphorylation of exogenous (histone III-S) and endogenous (37-kD protein) substrates. In conclusion, our results (a) provide clear evidence of a marked inhibitory effect of chenodeoxycholic acid on monocyte activation, suggesting a potential role of primary endogenous bile acids in the immune defect associated with cholestasis; and (b) indicate that the inhibition of monocyte activation by chenodeoxycholic acid is mediated by way of protein kinase C activation.

Alkaloids↗
PubMed1994

Two different incubation times for the activated partial thromboplastin time (APTT): a new criterion for diagnosis of lupus anticoagulant.

We describe a test for LA based on the specific APTT behaviour of LA plasmas when the incubation time with the APTT reagent is increased from 1 to 20 min. "1-10 APTT" test was defined as the difference (s) between results of the APTT performed with 1 and the one performed with 10 min incubation. A test value > 11 s (upper normal limit determined on 134 normal plasmas) was considered positive for a LA. The test distinguished all the LA patients studied (n = 40) from patients with factor VIIIc inhibitors, patients receiving heparin or warfarin therapy and also patients with congenital factor deficiencies, except those with prekallikrein and factor XII deficiencies. The test detected LA in warfarin (n = 3) and in heparin (n = 2) LA anticoagulated patients. Among 195 patients referred for LA screening, the test detected LA in 5 patients with normal standard APTT. This simple test, using a single reagent for screening and confirmatory procedures is sensitive and fairly specific for LA when combined with mixing studies. However, since the test was defined using one APTT reagent, the performances of other reagents have to be assessed.

Abortion, Habitual↗
PubMed1993

[Malignant neonatal tumors].

Malignant neonatal tumors are rare (2% of childhood cancers, 1-2 cases/30,000 births). However, specificities in diagnosis and therapy must be underlined at this period of life; furthermore, the possibilities of antenatal sonographic diagnosis are improving and it may contribute to increase their incidence. Topographic analysis allows etiologic investigations since these tumors have the same diagnostic features as compared with older children, except Pepper's syndrome and leukemias. Therapeutic management depends on a rather good prognosis and fragility of such newborn. Indeed, surgical excision is the main step of treatment. Radiotherapy must be avoided whenever possible. Chemotherapy may be indicated (metastatic or unresectable tumors, omission or delay of irradiation in brain tumors) and has to be elaborated cautiously, according to the peculiar physiology of the neonate. Whatever the therapeutic strategy is, neonatal homeostasis must be well balanced, which implies a multidisciplinary specialized team. Respecting these conditions will help to cure more than the present 50% and better for future well being of such children.

Abdominal Neoplasms↗
PubMed1993

Cell-surface display of heterologous epitopes on Staphylococcus xylosus as a potential delivery system for oral vaccination.

A system has been developed for the surface expression of heterologous receptors on the cell surface of Staphylococcus xylosus. Gene fragments encoding peptides to be displayed on the cell surface can be assembled by applying a polymerization strategy based on the class-IIS restriction enzyme BspMI and thereafter subcloned into an Escherichia coli-staphylococci shuttle vector designed for targeting of produced fusion proteins to the outer cell surface of the Gram-positive host cell. A heterologous receptor was genetically assembled and expressed on the surface of S. xylosus where the separate regions could be independently probed in immunogold assays, using antisera reacting with different regions of the recombinant receptor. In addition, a receptor-specific humoral immune response could be elicited in mice by oral immunization with recombinant S. xylosus cells, suggesting that these type of Gram-positive bacteria might offer potential vehicles for oral vaccination.

Administration, Oral↗
PubMed1993

Analysis of performance of prepubertal swimmers assessed from anthropometric and bio-energetic characteristics.

The relationship between anthropometric and bio-energetic data and timed performance over 50 to 400 m was studied in 25 young male swimmers [11.3 (SD 1) years]. Anthropometric measurements included height, body mass, body fat mass, body area, thoracic section area (Ats) thoracic circumferences, lengths of upper limb, bi-acromial and bi-iliac diameters. Maximal oxygen consumption (VO2max; direct method), maximal anaerobic power (W(an),max; force-velocity test) and mean power in 30 s sprint (W30 s; Wingate test) were also measured. Each of these bio-energetic variables was expressed in absolute terms, relating to body mass, body area and Ats. The stepwise regression method was used to determine contribution of the variables (anthropometric and/or bio-energetic) of the time achieved over the distance. The W30 s/Ats accounted for 46% of the time over 50 m (negative correlation). The VO2max/Ats and height were negatively correlated with the times of performances over 100 m, 200 m and 400 m, these two variables accounted for 71% to 77% of the performance. These results would indicate that even in young boys, anthropometric and bio-energetic characteristics are both important in swimming performance, particularly the bio-energetic variables expressed per Ats.

Body Composition↗
PubMed1993

Infection due to Rhizomucor pusillus: report of four cases in patients with leukemia and review.

Rhizomucor pusillus, a thermophilic fungus of the order Mucorales, is a rare cause of human infection. A search of the literature has produced only seven reports describing nine cases of infection caused by this organism. Recently, over a period of 17 months, four cases of R. pusillus infection in patients with leukemia were diagnosed: a cluster of three cases in a Montreal hospital and one isolated case from Quebec City. All four cases were proven both by histopathologic examination and by culture of tissues. In three cases, pulmonary involvement was confirmed following lung surgery, and in one case, disseminated infection was observed at autopsy. All patients received amphotericin B, and two underwent surgical debridement; however, none of the patients survived.

Adolescent↗
PubMed1993

Pharmacokinetics and platelet antiaggregating effects of beraprost, an oral stable prostacyclin analogue, in healthy volunteers.

Beraprost sodium (BPS) is an orally stable analogue of prostacyclin that inhibits adenylate-cyclase-dependent platelet aggregation and is proposed for treatment of chronic arterial occlusion. To determine the duration and intensity of platelet antiaggregation with BPS, 12 healthy, nonsmoking, male white volunteers participated in a double-blind, dose-escalating design with randomized placebo, placebo-controlled, cross-over study. After overnight fasting, single (20, 40, 60 micrograms and placebo) and repeated [20, 40, 60 micrograms and placebo) and repeated [20, 40, 60 micrograms and placebo three times daily (t.i.d.) for 3 days] oral doses of BPS were administered. Mean percentage of inhibition of ADP-induced aggregation normalized to placebo was measured for 8 h after drug administration and related to plasma concentrations (Cp) of the active enantiomer (APS 314d). BPS 40 and 60 micrograms decreased platelet aggregation 1 h after single doses, and 0.5 h and 1 h after repeated doses. BPS 20 micrograms had no significant effect. APS 314d pharmacokinetics was linear, and its terminal half-life (t 1/2) ranged from 0.50 +/- 0.21 to 0.91 +/- 0.27 h (mean +/- SD) independently of BPS dose. Antiaggregating effects were poorly related to Cp of APS 314d (r2 < or = 0.2). Some subjects complained of moderate postdrug absorption headaches (7 of 12 after single and 8 of 12 after repeated doses) and flushes (6 of 12 and 7 of 12, respectively). These data indicate that orally active prostacyclin BPS (40 or 60 micrograms) exerts its maximal antiaggregating effects between 0.5 and 1 h.

Administration, Oral↗
PubMed1993

High incidence of Epstein-Barr virus detection in Hodgkin's disease and absence of detection in anaplastic large-cell lymphoma in children.

By in situ hybridization with EBER oligonucleotides and immunohistochemistry with anti-latent membrane protein 1 (LMP1) antibody, we compared the detection rate of Epstein-Barr virus (EBV) in Hodgkin's disease and anaplastic large-cell lymphomas in children. Among the 13 cases of Hodgkin's disease tested, 7 (54%) were found to be EBV associated (EBER transcripts +, LMP1 +). None of the 11 cases of ALC lymphomas was found to contain EBV genomes or gene products. This may indicate that EBV is not a pathogenic agent in anaplastic large-cell lymphomas in children in comparison to Hodgkin's disease.

Adolescent↗
PubMed1993

Gentamicin administered during gestation alters glomerular basement membrane development.

Gentamicin during gestation alters glomerular basement membrane development. A drug-induced nephrotoxicity was described for neonates after gentamicin was given intraperitoneally to pregnant Wistar rats; glomerular alterations and changes in permselectivity were important. We investigated the ultrastructure of the glomerular basement membrane (GBM), the arrangement of anionic sites, and the urinary proteins at two ages, with 1-day- and 12-month-old control and prenatally exposed animals. For neonates, the pattern of glomerular differentiation was similar, anionic sites were made of heparan sulfate proteoglycans, and the GBM had the same total thickness in both groups. After transplacental gentamicin exposure, the lamina densa was larger; the laminae rarae were thinner; the density of anionic sites was increased; the levels of hydroxyproline, sulfate, and hexuronic acid in the kidney were increased; and the immunoelectrophoresis of urinary proteins was abnormal. For adults, prenatal exposure to gentamicin led to altered juxta-medullary glomeruli with a larger GBM and abundant anionic sites, especially in the lamina densa, and to a protein excretion different from that of controls. Thus, gentamicin administered during pregnancy leads to permanent alterations of the GBM with modifications of both the layers and the anionic sites, possibly because of a perturbed protein metabolism. These altered glomeruli are at risk during life and could be the starting point for a kidney disease.

Animals↗
PubMed1993

Intracellular free Ca2+ and vasoconstriction determined simultaneously in the perfused rat tail artery.

To measure, simultaneously, intracellular free Ca2+ ([Ca2+]i) and vasoconstriction in a perfused vessel, we used the fluorescent Ca2+ indicator fura 2 with a dual-wavelength excitation method. One-centimeter-long segments of the caudal artery were dissected from 12-mo-old male Wistar rats. The endothelium was removed by gentle rubbing. The artery was mounted in a specially constructed spectrofluorometer cuvette, perfused with oxygenated physiological saline solution at 37 degrees C, and loaded by perfusion with fura 2 acetoxymethyl ester (5 microM) over a 90-min period. This paper is a description of the technique and the experiments that validate it as a useful method for examining Ca(2+)-related vascular reactivity in an intact perfused vessel.

Animals↗
PubMed1993

Hemodynamic and mechanical determinants of myocardial O2 consumption in normal human heart: effects of dobutamine.

The relationship of myocardial O2 consumption (MVO2) to its potential hemodynamic and mechanical determinants was investigated in eight healthy normal volunteers at rest and during infusion of dobutamine (5-10 micrograms.kg-1.min-1). MVO2 was calculated from the monoexponential myocardial clearance of [1-11C]acetate with positron emission tomography, and left ventricular mechanical function was assessed by two-dimensional echocardiography. Infusion of dobutamine increased heart rate by 53%, the tension-time index by 31%, and the rate-pressure product by 116%. Cardiac output (+70%), left ventricular ejection fraction (+24%), total mechanical energy [systolic pressure-volume area, (PVA) +84%], and left ventricular pressure-work index (+100%) also increased during infusion of dobutamine. During infusion of dobutamine, MVO2 increased from 96 +/- 17 to 233 +/- 19 J.min-1.100 g left ventricle-1, while myocardial efficiency (the ratio of PVA to MVO2) decreased from 46 +/- 8 to 35 +/- 4% (P < 0.001 each). MVO2 was best correlated (P < 0.001) with the PVA (r = 0.92) and the pressure-work index (r = 0.92). Infusion of dobutamine also resulted in a significant parallel upward shift of the PVA-MVO2 relationship, indicative of an increase in PVA-independent MVO2. Our data indicate that, in human subjects, MVO2 is mainly related to systolic PVA and that inotropic stimulation with dobutamine results in decreased efficiency of contraction, such as that previously described in isolated hearts.

Acetates↗