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Biomedical subjects

R Schmid

Publications and source records attributed to R Schmid.

At least 163 records · Page 9Linked to original sources
PubMed1993

Does oligodendrocyte survival depend on axons?

BACKGROUND: We have shown previously that oligodendrocytes and their precursors require signals from other cells in order to survive in culture. In addition, we have shown that about 50% of the oligodendrocytes produced in the developing rat optic nerve normally die, apparently in a competition for the limiting amounts of survival factors. We have hypothesized that axons may control the levels of such oligodendrocyte survival factors and that the competition-dependent death of oligodendrocytes serves to match their numbers to the number of axons that they myelinate. Here we test one prediction of this hypothesis - that the survival of developing oligodendrocytes depends on axons. RESULTS: We show that oligodendrocyte death occurs selectively in transected nerves in which the axons degenerate. This cell death is prevented by the delivery of exogenous ciliary neurotrophic factor (CNTF) or insulin-like growth factor I (IGF-1), both of which have been shown to promote oligodendrocyte survival in vitro. We also show that purified neurons promote the survival of purified oligodendrocytes in vitro. CONCLUSION: These results strongly suggest that oligodendrocyte survival depends upon the presence of axons; they also support the hypothesis that a competition for axon-dependent survival signals normally helps adjust the number of oligodendrocytes to the number of axons that require myelination. The identities of these signals remain to be determined.

Journal Article↗
PubMed1993

Effects of N-terminal truncations upon chloroplast NADP-malate dehydrogenases from pea and spinach.

Using the purification procedure of Fickenscher and Scheibe (Biochim. Biophys. Acta 749 (1983), 249-254) and a modification of the method, we produced a series of NADP-MDH forms from spinach and pea-leaf extracts that were characterized by a stepwise shortening of the N-terminal sequences. Limited proteolysis of the enzymes resulted in the generation of even shorter forms. Immunoprecipitation of the NADP-MDH from crude extracts revealed that the sequences of the intact enzymes from pea, spinach and maize started at a position (Ser) identical with that established for the Sorghum enzyme (Crétin, C., et al. (1990) Eur. J. Biochem. 192, 299-303). Spinach NADP-MDH isolated by conventional methods was shown to represent the intact form. Thus, the kinetic, regulatory and structural properties of the various truncated forms could be compared with those of an intact form. Removal of 5 or 11 amino acids, as occurred during isolation of the pea NADP-MDH, was without any significant effect. The enzymes were all dimeric and still exhibited the characteristic redox-regulatory properties. However, removal of 31 and 37 amino acids using aminopeptidase K resulted in the formation of active monomers characterized by only slightly lowered affinities towards the substrates, a shift of their pH optimum from 8 to 7, the loss of oxaloacetate inhibition and an increased maximal velocity. Although these forms lacked most or all of the N-terminal extra-peptide, including the 2 cysteines involved in redox-modification, they were still sensitive to the redox-potential. However, the low concentration of thiol required for immediate and complete restoration of any lost activity (40 mM beta-mercaptoethanol) suggested that this reaction might not be relevant for redox-regulation in vivo.

Amino Acid Sequence↗
PubMed1993

Identification, cloning, and expression of the gene for adenylate kinase from the thermoacidophilic archaebacterium Sulfolobus acidocaldarius.

An adenylate kinase gene from a member of the archaebacterial kingdom, the thermoacidophilic archaebacterium (archaeon) Sulfolobus acidocaldarius, has been cloned and sequenced for the first time. Two degenerate oligonucleotide probes, based on the N-terminal amino acid sequence information, led to the amplification of a gene-specific DNA fragment, used to screen subgenomic libraries. Comparing the DNA-derived amino acid sequence of total 194 residues with those of known procaryotic and eucaryotic adenylate kinases revealed only a low degree of similarity, except for a glycine-rich region close to the N-terminus, the so-called P-loop. Using inducible expression systems catalytically active S. acidocaldarius adenylate kinase was produced in large amounts. Although the total length of the protein and the results of alignment procedures suggest a closer relation to eucaryotic than to procaryotic sequences, the archaebacterial enzyme may represent a novel class of adenylate kinases. This is corroborated by the finding that an antiserum against this protein does not cross-react with Escherichia coli nor yeast or rabbit adenylate kinases for example.

Adenylate Kinase↗
PubMed1993

Transient, specific and extremely rapid release of osmolytes from growing cells of Escherichia coli K-12 exposed to hypoosmotic shock.

The influence of hypoosmotic shock on the solute content of growing Escherichia coli K-12 cells was investigated at 37 degrees C. Within 20 s after the shock the cells had released most of their osmolytes K+, glutamate and trehalose. This release was specific and not due to rupture of the cell membrane, since under these conditions i) the cells neither lost protein nor ATP, ii) [14C]-labeled sucrose did not enter the cytoplasm from the periplasm, and iii) except for their glutamate and aspartate level, which decreased, the amino acid pool of alanine, lysine and arginine of the cells remained approximately constant. Within a minute after the shock the cells started to reaccumulate parts of their previously released glutamate, aspartate and K+, but not trehalose and resumed growth within 10 min after the shock. Experiments with K(+)-transport mutants showed that none of the genetically-identified K+ transport systems is involved in the K(+)-release process. Reaccumulation of K+ took place via the uptake systems TrkG and TrkH. The possibility is discussed that the exit of solutes after hypoosmotic shock occurs via several stretch-activated channels, which each allow the release of a specific osmolyte.

Adaptation, Physiological↗
PubMed1993

Multiple extracellular signals are required for long-term oligodendrocyte survival.

We showed previously that oligodendrocytes and their precursors require continuous signalling by protein trophic factors to avoid programmed cell death in culture. Here we show that three classes of such trophic factors promote oligodendrocyte survival in vitro: (1) insulin and insulin-like growth factors (IGFs), (2) neurotrophins, particularly neurotrophin-3 (NT-3), and (3) ciliary-neurotrophic factor (CNTF), leukemia inhibitory factor (LIF) and interleukin 6 (IL-6). A single factor, or combinations of factors within the same class, promote only short-term survival of oligodendrocytes and their precursors, while combinations of factors from different classes promote survival additively. Long-term survival of oligodendrocytes in vitro requires at least one factor from each class, suggesting that multiple signals may be required for long-term oligodendrocyte survival in vivo. We also show that CNTF promotes oligodendrocyte survival in vivo, that platelet-derived growth factor (PDGF) can promote the survival of oligodendrocyte precursors in vitro by acting on a novel, very high affinity PDGF receptor, and that, in addition to its effect on survival, NT-3 is a potent mitogen for oligodendrocyte precursor cells.

Animals↗
PubMed1993

Homogeneous immunofluorometric assays of alpha-fetoprotein with macroporous, monosized particles and flow cytometry.

We evaluated two homogeneous immunofluorometric assays (IFMAs) of alpha-fetoprotein (AFP) based on new macroporous acrylate particles combined with flow cytometry. The standard IFMA, requiring 1 h of incubation, provided a working range from 1.8 to > 900 kIU/L (CV < 10%) and a detection limit of 0.6 kIU/L. Use of overnight incubation and a lower particle concentration extended the working range by 1 decade in the lower end. Analytical recoveries for the standard IFMA varied between 97% and 108%. The slope and y-intercept of the regression line correlating measurements by the standard IFMA and a routine immunoradiometric assay were not significantly different from 1 and 0, respectively (P > 0.5), and the correlation coefficient was 0.996. High precision and warning of spuriously high measurements were obtained by including in each sample separate particle types for detecting instrument instability and measuring nonspecific binding only.

Acrylates↗
PubMed1993

Effect of a postprandial amino acid pattern on gastric acid secretion in man.

In the present study it was the aim to examine the effect of a postprandial plasma amino acid pattern on gastric acid secretion in man. Firstly, a new amino acid mixture of 18 amino acids was administered intravenously (10 g/h) to 8 normal subjects and the plasma amino acid levels correlated well with those observed after ingestion of a protein-rich meal (r = 0.91; p < 0.001). The i.v. administration of this solution elicited a small though significant augmentation of basal acid secretion (3.1 mmol/h) compared to controls while pentagastrin-stimulated (50 ng/kg/h) gastric acid secretion remained unaffected. In addition, plasma gastrin levels remained unchanged in the basal state during i.v. infusion of the amino acid solution. These results indicate that elevations of circulating plasma amino acid levels similar to those after ingestion of a protein-rich meal have--if at all--only a small stimulatory effect on basal acid secretion. Since plasma amino acids increase when gastric acid secretion has already been activated by cephalic or gastric phase mechanisms, their physiological relevance for the regulation of gastric acid secretion is negligible.

Adult↗
PubMed1993

[Intraoperative aspiration and reinfusion of autologous blood in resection of abdominal aortic aneurysms with Solcotrans plus].

Quantitative and qualitative assessment of intraoperative aspiration and reinfusion of autologous blood with the Solcotrans was carried out in 11 males (52-79 years) undergoing elective resection of abdominal aortic aneurysms. Hematology, blood chemistry, coagulation parameters and complement activation were studied in the patient's blood at the following time points: preoperatively, before and after heparinisation, after retransfusion of the first and last Solcotrans, 6 and 20 hours postoperatively. In addition the same quality control was performed in the first and last Solcotrans blood. Results (mean values of 11 patients +/- 1 SD): Intraoperatively 2-3 Solcotrans units were salvaged (total 1039 +/- 565 ml) of which 805 +/- 487 ml were retransfused to the patients. As a mean patients required only 1 unit of homologous RBC's (395 +/- 781 ml) intraoperatively. Patient's intraoperative hemoglobin concentration amounted to 10 g/dl or more. Whereas the hemoglobin level in the Solcotrans attained only 8.2 g/dl. Thrombocyte counts (48 +/- 18 x 10(9)/l) and ionized calcium (0.2 +/- 0.4 mmol/l) were significantly depressed when compared to the preoperative patient values (p < 0.05). The protein concentration remained within normal limits in the patient's and in the Solcotrans blood. Complement activation (C4a, C5a [des Arg]) showed a significant increase after initiation of surgery and there was no significant difference between the solco- or patient blood. Whereas plasma free hemoglobin, coagulation and fibrinolysis parameters showed a significant elevation in the Solcotrans blood. In conclusion the solcotrans system offers a fast, efficient and simple method for salvage and retransfusion of intraoperative autologous blood.

Aged↗
PubMed1992

Purification and properties of lipase from Penicillium simplicissimum.

A Penicillium simplicissimum strain has been found to produce an inducible extracellular lipase. Triolein was the best inducer for the enzyme production with the highest activity being achieved after 48 h of incubation. The purified lipase showed a molecular weight of 56,000 by SDS-PAGE. The enzyme exhibited a high ratio of apolar amino acids. The lipase was stable in the pH range of 5-7 and at 50 degrees C for 15 min. The optimum assay conditions were 37 degrees C and pH 5.0. The enzyme showed a high stability in water immiscible organic solvents. Lipase from P. simplicissimum is nonspecific and hydrolyses each of the three bonds of triacylglycerols.

Amino Acids↗
PubMed1992

Contribution of neural intrapancreatic non-cholinergic non-adrenergic mechanisms to glucose-induced insulin release in the isolated rat pancreas.

In the isolated rat pancreas the effect of intrapancreatic non-adrenergic non-cholinergic nerves was examined upon insulin, glucagon and somatostatin release during perturbations of perfusate glucose. Elevation of glucose from 1.6 to 8.3 mmol/l increased insulin and somatostatin secretion and inhibited glucagon release. The first phase of insulin secretion was significantly reduced by the neurotoxin tetrodotoxin to 55% of the controls (p < 0.05). The somatostatin response was attenuated by tetrodotoxin while the change of glucagon remained unaffected. In contrast the combined adrenergic and cholinergic blockade with atropine, phentolamine and propranolol (10(-5) mol/l) did not modify the insulin, glucagon and somatostatin response. When glucose was changed from 8.3 to 1.6 mmol/l, the reduction of insulin and somatostatin release was not modified by tetrodotoxin, but stimulation of glucagon was significantly attenuated by 60-70% (p < 0.03), which was similar to the effect of combined adrenergic and cholinergic blockade. Subsequently, the effect of neural blockade was examined during more physiological perturbations of perfusate glucose levels. When glucose was changed from 3.9 to 7.2 mmol/l, tetrodotoxin also attenuated first phase insulin response by 40% while cholinergic and adrenergic blockade had no effect. The nitric oxide synthase inhibitor NG-Nitro-L-arginine-methyl-ester (L-NAME) did not alter the glucose-induced insulin response indicating that nitric oxide is not involved in this mechanism. It is concluded that neural non-adrenergic non-cholinergic mechanisms contribute to the first, but not second phase of glucose-induced insulin release. Non-adrenergic non-cholinergic effects do not participate in regulation of glucagon and somatostatin secretion under the conditions employed.(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of Variance↗
PubMed1992

Long term monitoring of immunoreactive endothelin-1 and endothelin-3 in ventricular cerebrospinal fluid, plasma, and 24-h urine of patients with subarachnoid hemorrhage.

Endothelins (ETs), peptides that were originally isolated from endothelial cells, have extremely potent and long-lasting vasoconstricting effects on cerebral vessels in vitro and in vivo. Observations that astrocytes produce these peptides and that their ET production can be stimulated, e.g. by thrombin, and potentiated via a self-enhancing autoregulatory mechanism may have shed new light upon the pathogenesis of cerebrovasospasm (CVS). ETs are present at low levels in normal human cerebrospinal fluid (CSF). Few and contradictory reports exist on ET levels in subarachnoid hemorrhage (SAH)-associated CVS. We monitored ventricular CSF, plasma, and 24-h urine levels of immunoreactive endothelin-1 (ET-1) and endothelin-3 (ET-3) in seven patients with SAH, who did (five) or did not (two) develop CVS in the course of their disease, as well as in two patients with different conditions (acoustic neuroma/postoperative meningitis; hydro-/hematocephalus) over 7-19 days. A distinct peak of both ET-1 and ET-3 in CSF of patients with SAH coincided with clinically documented signs of CVS and was absent in CSF of patients with SAH but no CVS. CSF levels of ET-1 and ET-3 displayed a striking parallelism in all subjects. Plasma ET-1 levels were essentially in the normal range. ET-3 was not detectable in plasma under our assay conditions. The excretion profiles of ET-1 and ET-3 in 24-h urine revealed again a predominantly parallel behavior of the two peptides. Interestingly, patients with high ET levels in CSF showed simultaneous peaks in urinary ET excretion, expressed as nanograms per gram of creatinine. Our findings support an association of ETs with the pathogenic events following SAH. The well-documented effects of these peptides on cerebral vessels suggest they are mediators rather than markers of disease.

Adult↗
PubMed1992

The use of plasma levels to optimize methadone maintenance treatment.

The question of the optimal methadone dose during maintenance therapy is controversial. For both philosophical and practical reasons, therapeutic drug monitoring has not been generally used. Some therapists prescribe low doses of methadone more for psychological than pharmacological reasons. This study examines, in 104 methadone patients, the relation between self-rating, observer-rating, urine tests, HIV-1 sero-status, daily methadone doses and plasma levels of methadone. No differences were found between HIV-1 infected and seronegative patients in these respects. The optimal methadone plasma level as judged by self- and observer-rating was more than 150 ng/ml. For oral methadone, the best results are obtained in patients receiving more than 90 mg daily. We found a significant relationship between methadone dose and plasma levels, also in patients who also used illicit drugs. We conclude that therapeutic drug monitoring should become routine in methadone treatment to achieve optimum results, especially in patients who complain of withdrawal symptoms and continue high-risk behaviour.

Adult↗
PubMed1992

A piezoelectric immunobiosensor for atrazine in drinking water.

A piezoelectric crystal immunobiosensor has been developed for the assay of atrazine herbicides in drinking water. Determinations from 0.03-100 micrograms l-1 (parts per billion) of atrazine can be made with a relative SD of about +/- 8%. Atrazine antibodies (polyclonal from sheep) are layered onto the gold electrode of 10 MHz piezoelectric crystals, which are precoated with protein A. The sensor is reversible, being reusable for about eight or nine assays.

Atrazine↗
PubMed1992

Contribution of postprandial amino acid levels to stimulation of insulin, glucagon, and pancreatic polypeptide in humans.

The present study was designed to examine the contribution of the postprandial increase of plasma amino acids after ingestion of a protein-rich meal to the rise of the three pancreatic hormones insulin, glucagon, and pancreatic polypeptide (PP). A mixed amino acid solution was designed, which permitted a fairly close imitation of the arterial plasma pattern of the 21 amino acids that rise after ingestion of a 200-g porcine steak meal. In 10 healthy subjects the intravenous infusion of this mixed amino acid solution at a rate of 10 g/h elicited a rise of the 21 amino acids examined that correlated well with the postprandial increase (r = 0.89, p < 0.001). The maximal rise of plasma insulin (64 +/- 5 pmol/L) and glucagon (630 +/- 21 ng/L) was not significantly different from the postprandial increase of these two hormones (49 +/- 4 pmol/L and 780 +/- 28 ng/L, respectively). PP levels rose by 316 +/- 33 ng/L postprandially, which was clearly above the increase of 112 +/- 13 ng/L during intravenous amino acids (p < 0.01). In conclusion, the present data demonstrate that the postprandial rise of amino acid levels in arterialized venous plasma can account for most if not all of the postprandial increase of insulin and glucagon during the ingestion of a protein-rich meal. In contrast, only 35% of postprandial PP levels can be ascribed to the rise of plasma amino acids. In contrast to the effect of carbohydrate-rich meals, an enteric augmentation of insulin release seems to be of minor and possibly of no importance during ingestion of protein-rich meals.

Adult↗
PubMed1992

Stress proteins and cross-protection by heat shock and salt stress in Bacillus subtilis.

Bacillus subtilis induced a set of general stress proteins in response to a salt or heat stress. Cells subjected to a mild heat stress showed a protective response which enabled them to survive otherwise lethal temperatures (e.g. 52 degrees C). In a similar way bacteria were enabled to survive toxic concentrations of NaCl by pretreatment with lower salt concentrations. A mild heat shock induced a cross-protection against lethal salt stress. The pretreatment of cells with low salt, however, was less effective in the induction of thermotolerance than a preceding mild heat stress. Three stress proteins were identified on the basis of their N-terminal amino acid sequences as homologues of GroEL, DnaK and ClpP of Escherichia coli. The role of general and specific stress proteins in the induction of thermotolerance/salt tolerance and cross-protection is discussed.

ATP-Dependent Proteases↗
PubMed1992

Fluoride availability in human saliva after dentifrice use: correlation with anticaries effects in rats.

Studies were conducted to determine fluoride availability in saliva after dentifrice use and to relate this parameter to cariostatic efficacy in rat caries experiments. Three dentifrices--two commercial formulations (Colgate Winterfresh Gel and Crest Dentifrice with Na-Sr-polyacrylate) and an Experimental dentifrice--were compared with respect to salivary fluoride availability. All of the dentifrices tested contained 1100 ppm F as sodium fluoride. It was observed that the Experimental dentifrice and Crest dentifrice with Sr-polyacrylate exhibited low salivary fluoride availability relative to the Colgate Winterfresh Gel. Salivary fluoride availability was assessed by means of two parameters: (a) the fluoride concentration in the dentifrice saliva slurry expectorated after brushing, and (b) the area under the curve of salivary F concentration vs. time for up to two hours after dentifrice use. In two rat caries experiments, it was observed that both the Experimental dentifrice and the Sr-polyacrylate dentifrice provided less cariostatic efficacy than the clinically validated Positive Control (Colgate Winterfesh Gel). Analysis of these data provides further evidence in support of the concept that fluoride availability in saliva following dentifrice use is an important parameter related to anticaries efficacy.

Acrylic Resins↗