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Biomedical subjects

L Stephan

Publications and source records attributed to L Stephan.

10 recordsLinked to original sources
PubMed2003

Laser-induced fluorescence with an OPO system. Part II: direct determination of lead content in seawater by electrothermal atomization-laser-excited atomic fluorescence (ETA-LEAF).

Fluorescence was induced by coupling a laser with an optical parametric oscillator (OPO) to develop an analytical method for the direct determination of lead content, at ultra-trace level, in seawater by electrothermal atomization-laser-excited atomic fluorescence (ETA-LEAF). The optimization of atomization conditions, laser pulse energy, and mainly temporal parameters allowed us to reach a 3 fg detection limit (0.3 ng L(-1)) despite the low repetition rate of the device. The expected error on predicted concentrations of lead, at trace levels, in seawater was below 15%.

Journal Article↗
PubMed2002

Laser-induced fluorescence with an OPO system. Part I. Optimisation of the analytical system by use of experimental design methodology. Application to the direct quantification of traces of benzo[ a]pyrene.

This study deals with the optimisation and application of a method for direct analysis of trace pollutants in water by laser-induced fluorescence. The arrangement used consisted of an Nd:YAG Laser coupled with an optical parametric oscillator (LYOPO) and connected to a spectrophotometer and a high-sensitivity camera. Optimisation was achieved by developing an experimental design methodology to maximise the signal-to-noise ratio and reduce the limit of detection. The technique was then applied to the detection of benzo[ a]pyrene in water. The experimental results were evidence of its high sensitivity and time-resolution potential. The detection limit for benzo[ a]pyrene was 0.7 ng L(-1) in drinking water and 4 ng L(-1) in raw water containing 1 mg L(-1) humic acids.

Benzo(a)pyrene↗
PubMed1999

Maintenance treatment with medroxyprogesterone acetate in patients with advanced breast cancer responding to chemotherapy: results of a randomized trial. Essen Breast Cancer Study Group.

The purpose of this randomized phase III trial was to study whether medroxyprogesterone acetate (MPA) maintenance treatment prolongs the time to progression in advanced breast cancer patients responding to an induction chemotherapy. Patients with progressive advanced breast cancer previously untreated with anthracylines and progestins were given epirubicin (30 mg/m2) and ifosfamide (2 g/m2) on days 1 and 8 at 3-weekly intervals. Patients without disease progression after 6 cycles of chemotherapy were randomly assigned to receive, until progression, either no treatment or MPA at a daily total dose of 500 mg. Ninety patients were randomized: 46 to the MPA arm and 44 to the observation arm. Median time to progression was longer in the MPA arm: 4.9 months versus 3.7 months in the intent-to-treat analysis (p = 0.02), and 4.9 months versus 3.0 months in the secondary efficacy analysis (p = 0.012). Seven patients were removed from MPA due to side effects. The changes in patient-rated quality of life scores were similar in both groups. The median length of survival from randomization was 17.4 months for patients receiving MPA and 18.3 months for patients randomized to observation (p = 0.39). In conclusion, in patients with advanced breast cancer achieving remission or non-progression with 6 cycles of epirubicin and ifosfamide chemotherapy, MPA maintenance treatment led to a significant, though modest, prolongation of the time to progression without affecting overall survival of the study patients.

Aged↗
PubMed1992

The effect of illness duration on perceptual asymmetry in schizophrenia.

Perceptual asymmetry in a group of schizophrenic subjects who were clinically stable and living in the community was compared with a group of normal control subjects matched for age and sex using a dichotic monitoring task of language processing. Schizophrenic subjects showed reduced target detection and slower reaction times for both left and right ear inputs. In relation to performance asymmetry, the schizophrenic subjects had a reduced speed of responding to left ear items compared to normal controls. Within the schizophrenic group differences in performance emerged according to duration of illness. Shorter duration of illness was associated with poorer target detection overall and comparatively greater magnitude of the normal right ear advantage. The latter was accounted for by a relative augmentation of the normal left ear performance decrement. These results were partly reflected in the reaction time measures. The findings suggest that as illness duration increases there may be a tendency for certain aspects of the information processing abnormality in schizophrenia to normalise, in spite of continued deficits as reflected in prolonged reaction times.

Adult↗
PubMed1991

Pressure effects on the binding of vanadate to the sarcoplasmic reticulum calcium-transport enzyme.

The effect which hydrostatic pressure exerts on the binding of vanadate to the calcium-transport enzyme was determined. The recent unavailability of radioactive vanadate prevented direct measurements of vanadate binding. The vanadate-free enzyme fraction was instead monitored by phosphorylating it with ATP according to Medda and Hasselbach [Medda, P. & Hasselbach, W. (1983) Eur. J. Biochem. 137, 7-14]. Vanadate binding is reduced with rising pressure at first markedly and subsequently, above 30 MPa, relatively little. The biphasic pressure-binding relationship was analysed by applying a biexponential fitting procedure to the experimental data. The biphasicity of the pressure-binding relationship indicates that the description of vanadate binding requires at least a two-step reaction sequence. The volume increments which predominate at lower pressure values, range from 200-400 ml.mol-1 depending on the composition of the reaction medium containing 5 microM and 20 microM vanadate and no or 15% (by vol.) Me2SO. The binding volumes deduced for the higher pressure range amount to 20-40 ml.mol-1. Vanadate binding is reduced in the presence of 30 microM calcium, and simultaneously both binding volumes are diminished by 100 ml.mol-1 and 20 ml.mol-1 for the low and high pressure values, respectively, as one can expect for mutual interactions between the two ligands of the transport enzyme.

Adenosine Triphosphate↗
PubMed1990

Effect of pressure and calcium on the reversible inhibition of the sarcoplasmic-reticulum calcium-transport enzyme and on its tryptic cleavage pattern.

The reversible inhibition of the sarcoplasmic-reticulum calcium-transport enzyme by pressure at room temperature is accompanied by a significant enhancement of the accessibility of the enzyme to tryptic cleavage dependent on the presence of calcium. The calcium-transport enzyme activity was monitored with dinitrophenyl phosphate as substrate. Pressure in the range 0.1-100.0 MPa affects trypsin cleavage of the control substrate N-alpha-benzoyl-L-arginine-4-nitroanilide hydrochloride little in the presence and absence of calcium. In contrast, application of 100.0 MPa to the calcium-transport enzyme at room temperature accelerates subsequent tryptic cleavage at the T2 but not at the T1 cleavage site [C. J. Brandl et al. (1986) Cell 44, 597-607]. Pressure application during tryptic digestion likewise solely affects cleavage at T2 which proceeds slowly in the absence but rapidly in the presence of calcium. At atmospheric pressure in the absence of calcium and at high pressure in the absence and presence of calcium new cleavage sites are exposed giving rise to new subfragments B1-3 in addition to the established peptides A1 and A2. Under pressure and in the presence of calcium, A1 and A2 rapidly disappear indicating the presence of calcium-binding sites in these peptides. In contrast, the B1-3 peptides which are most likely derivates of the B fragment accumulate in the presence and absence of calcium. In contrast to tryptic cleavage at atmospheric pressure, tryptic cleavage of the A as well as the B fragment tends to completion under pressure. In parallel to the disappearance of the A and B fragments calcium-dependent substrate hydrolysis vanishes. Computation of activation volumes for pressure-induced reversible enzyme inhibition and for tryptic cleavage furnished closely related volumes of opposite signs of 20-40 ml/mol and 80-100 ml/mol in the ranges 0.1-40.0 MPa and 40.0-100.0 MPa, respectively. Thus pressure produces reversible changes in the calcium-transport enzyme which activates and modifies tryptic-cleavage patterns at the T2 site of the A segment and at sites in its subfragments in the presence of calcium, i.e. if the enzyme residues in its E1 state. In contrast tryptic cleavage of the B fragment is accelerated by pressure independently of the presence of calcium.

Animals↗
PubMed1987

Pressure effects on the interactions of the sarcoplasmic reticulum calcium transport enzyme with calcium and para-nitrophenyl phosphate.

The effect of hydrostatic pressure on calcium dependent p-nitrophenyl phosphate hydrolysis of the sarcoplasmic reticulum calcium transport enzyme has been investigated at different degree of enzyme saturation by calcium and Mg-p-nitrophenyl phosphate to distinguish between activation and binding volumes. The enzyme saturated by both ligands displays a significant dependence of the activation volume on pressure, rising from 20 ml/mol at atmospheric pressure (0.1 MPa) to 80 ml/mol at 100 MPa. At subsaturating concentration of Mg-p-nitrophenyl phosphate an activation volume of 35 ml/mol prevails between 0.1 and 40 MPa. At subsaturating concentration of calcium the activation volume approximates 80 ml/mol in the same pressure range. The binding volume for both substrates is likewise pressure dependent falling from 20 ml/mol to 0 ml/mol for Mg-p-nitrophenyl phosphate and rising from 67 ml/mol to 155 ml/mol for calcium. The pressure dependence of activation and binding volumes is analysed on account of a simplified reaction scheme yielding activation volumes and rate constants for individual reaction steps.

Animals↗
PubMed1976

[A case of testicular feminization with the karyotype 47, XXY (author's transl)].

A case of testicular feminization is described, who has the karyotype 47, XXY in all analysed metaphases from blood and skin cultures. The question is discussed whether the karyotype 47, XXY is compatible with the syndrome of testicular feminization and which conditions are required to allow the hitherto known transmission of testicular feminization in presence of the gonosomes XXY. A review of literature is given.

Adult↗