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Biomedical subjects

A Müller

Publications and source records attributed to A Müller.

At least 757 records · Page 42Linked to original sources
PubMedDate not supplied

Arrhythmias and infarction in the ischemic pig heart are not mediated by xanthine oxidase-derived free oxygen radicals.

Xanthine oxidase activities of pig myocardium and blood during and following myocardial ischemia were measured using HPLC, and electrochemical detection of hypoxanthine, xanthine and uric acid. Myocardial ischemia was produced by occluding the anterior descending coronary artery two-thirds of the way from its origin. There was no accumulation of either xanthine or urate in the ischemic pig myocardium during occlusion periods of 90 min, but there was a substantial accumulation of hypoxanthine. Similarly, there was no increase in myocardial xanthine or urate during the 30 min reperfusion following coronary artery occlusion periods of 15, 30, 60 or 90 min. Following in vitro incubation at pH 8 of myocardial homogenates or blood with either hypoxanthine or xanthine and NAD, no urate production was detectable. In contrast, significant amounts of xanthine and/or urate were produced, following addition of xanthine oxidase to the reaction mixtures. Additional in vitro experiments showed that the following pig tissues were lacking xanthine oxidase activity: left and right atrial appendage, left and right ventricle, interventricular septum, anterior descending and circumflex coronary arteries, ascending aorta, lung, and blood. Large amounts of xanthine oxidase (9.3 +/- 1.8 SEM mU/g wet weight, n = 7) were found in pig liver. In the ischemic pig heart, transmural infarction developed within 60 min of ischemia. Ventricular arrhythmias and fibrillation occurred most frequently within 45 min of ischemia and within seconds after reperfusion. These results showed that the pig heart and blood were xanthine oxidase deficient, suggesting that xanthine oxidase-derived free oxygen radicals were not involved in the cytotoxic and arrhythmogenic effects brought about by myocardial ischemia and/or reperfusion in the pig.

Animals↗
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Prearrhythmia: changes preceding arrhythmia, new aspects by epicardial mapping.

The aim of our studies was to examine the electrophysiological conditions prior to the onset of arrhythmia in order to analyze in more detail whether arrhythmia is a sudden event or whether there are early signs preceding arrhythmia. For this purpose a computer-assisted mapping system equipped with 256 AgCl-electrodes for unipolar epicardial multichannel-recording was constructed that provided high temporal and spatial resolution (4 kHz/channel; 1 mm interelectrode distance). The electrodes were fixed to the surface of an isolated rabbit heart (prepared according to the Langendorff-technique; constant perfusion pressure 70 cm H2O; Tyrode solution equilibrated with 95% O2 and 5% CO2 at 37 degrees C) covering nearly the whole heart's surface. The activation times at each electrode were determined as the timepoints of the fastest negative deflection of the epicardial potentials. From these data the origins of epicardial activation were determined ("breakthrough points", BTP), and for each electrode a vector was constructed giving direction and velocity of the epicardial activation. This analysis was carried out for single heart beats under control conditions, under arrhythmogenic conditions (induced either by lowering the K+ concentration from initially 5.4 to finally 2.0 mmol/l or by application of ouabain 0.1, 0.2 or 0.3 mumol/l) or during manifest arrhythmia. By comparison of heart beats under these various conditions with control conditions we determined the percentage of identical BTP (deviating less than 1 mm) and of similar vectors (deviating less than 5 degrees). Under control conditions 80% BTP remained unchanged over a period of 60 min and about 30% of the vectors were similar. Reduction of the extracellular K(+)-concentration or treatment with ouabain resulted in a progressive, concentration-dependent decline in BTP- or vector-similarity (in still rhythmically beating hearts). In some cases these treatments finally lead to variant forms of arrhythmia. Critical values for the onset of arrhythmia were a reduction to 45% BTP-similarity and 18% vector-field-similarity. From these results it is concluded that arrhythmia is preceded by a state characterized by a derangement of the typical activation pattern which may be called prearrhythmia.

Animals↗
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Heartbeat evoked potentials (HEP): topography and influence of cardiac awareness and focus of attention.

Heartbeat evoked potentials (HEP) were recorded from good and poor heartbeat perceivers under two conditions differing in focus of attention. Under the first condition (ATT), subjects were instructed to count their heartbeats. Under the second condition (DIS), subjects were distracted from their heartbeats by having them count external tones. Electrical brain activity was recorded from 19 electrodes. EEG epochs were triggered by the R wave of the EKG. Analyses of variance yielded a significant difference for focus of attention in HEP amplitudes at central electrodes (Cz, C3, and C4) in the latency range 350-550 msec post R wave. No significant differences occurred between good and poor perceivers. The interaction between the Group and Condition factors was significant at F4, C4 and T6. The potential map of good perceivers showed a fronto-temporal positivity, which was reduced in poor perceivers. Our data suggest that paying attention to an internal event such as the heartbeat can modify the cortical evoked response associated with that event.

Adult↗
PubMedDate not supplied

Cellular redox changes and response to drugs and toxic agents.

Cellular metabolism and, in particular, oxidation-reduction systems are linked to responses to drugs and toxic agents in several ways. Major connections are given by the NADPH/NADP+ system and the GSH/GSSG system. Intracellular reductive pathways generally use NADPH as the electron donor. From a toxicological point of view, NADPH can be considered both as a "detoxicant" and as a "toxicant". In the former case, NADPH supports the glutathione redox cycle by maintaining a negative redox potential of GSH to permit its detoxication functions to occur. NADPH is also the main donor for reducing equivalents in drug oxidations by the cytochrome P-450-dependent monooxygenase system which, with some notable exceptions, serves important purposes in detoxication. The sources of NADPH reducing equivalents depend on the nutritional state: major sources in the fed state are represented by the cytosolic pentose phosphate shunt dehydrogenases, whereas mitochondrial sources linked to isocitrate dehydrogenase provide the bulk of NADPH reducing equivalents in the fasted state. As a "toxicant", NADPH supports redox cycling reactions involving various drugs and other compounds of quinoid structure, aromatic nitro compounds and iron chelates with formation of superoxide anion radicals and subsequent formation of other oxygen derived radical species. This presentation focuses on recent work carried out with isolated hepatocytes and perfused rat liver with respect to "oxidative stress". The noninvasive techniques of measurement of low-level chemiluminescence and of volatile hydrocarbons (ethane, pentane) as well as glutathione release and calcium release have been employed.

Alcohol Oxidoreductases↗
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Clear lens extraction to correct high myopia.

PURPOSE: To assess the refractive outcome and postoperative complications in a single surgeon series of clear lens extraction for high myopia. SETTING: Ophthalmology Department, Cornea and Refractive Surgery Unit, Vall d'Hebrón Hospital, Autónoma University of Barcelona, Spain. METHODS: Forty-six clear lens extraction procedures performed in 37 patients from November 1992 to January 1994 by one surgeon were retrospectively analyzed. Capsule tear and vitreous loss, endothelial cell loss, preoperative and postoperative best corrected visual acuity and cycloplegic refraction, and retinal detachment occurrence were looked at. RESULTS: Capsule tear with vitreous loss occurred in one eye (2.17%). Mean endothelial cell loss was 2.6% during the first postoperative year. Best corrected visual acuity was 6/12 or better in 69.4% of eyes preoperatively and in 88.5% postoperatively. Mean cycloplegic refraction was -16.05 diopters (D) preoperatively; the residual cycloplegic refraction was within 1.00 D in 48.4% of eyes and within 2.00 D in 92.5% postoperatively. CONCLUSION: Because of its high predictability, stability, and low morbidity, we believe clear lens extraction is a reasonable refractive surgery option for middle-aged patients with myopia.

Adult↗
PubMedDate not supplied

Tooth enamel as a detector material for retrospective EPR dosimetry.

Different methods of spectra evaluation and dose reconstruction in retrospective EPR dosimetry with tooth enamel have been compared in this study. Experiments with teeth irradiated with known doses have shown that dosimetry above 1 Gy using a dose effect curve is, with a standard deviation of 10%, the best method. As a second result it is shown that dosimetry down to 100 mGy with a standard deviation of 15% is possible.

Biometry↗
PubMedDate not supplied

[Visceral leishmaniasis. Personal observation and review of epidemiology, clinical aspects and therapy].

A 5 year old German girl contracted visceral leishmaniasis during a vacation in Spain, either 32 or 20 month prior to the manifestation of disease. She presented with fever, hepatosplenomegaly and pancytopenia. A bone marrow aspirate proved the diagnosis. Therapy with a pentavalent antimony drug brought about immediate improvement. Visceral leishmaniasis has to be suspected in individuals with fever, hepatosplenomegaly and pancytopenia who have resided in endemic areas (Mediterranean countries, India, East Africa, South America) during the previous years. If untreated, visceral leishmaniasis runs a fatal course. Therefore, early diagnosis by morphological and serological means and specific therapy with pentavalent antimony drugs are mandatory.

Animals↗
PubMedDate not supplied

[10 years follow-up of athrodeses of the hindfoot joints and upper ankle joint].

PURPOSE: What is the clinical and radiographic outcome of arthrodeses at the hindfoot and at the ankle more than 10 years postoperatively? METHODS: Between 1968 and 1988, 155 arthrodeses (ankle joint, triple arthrodeses, subtalar, pantalar and talonavicular arthrodeses) were performed on 147 patients. Indications for arthrodesis were posttraumatic arthritis, congenital deformity, idiopathic degenerative arthritis and rheumatoid arthritis. A variety of internal fixation devices or no internal fixation were used. 79 patients with 82 arthrodeses were reexamined clinically and radiographically, after 11.1 years on average. Static and dynamic foot print measurements were recorded with a capacitive sensor system. Another 26 patients with 27 arthrodeses replied to a questionnaire. RESULTS: Subjectively, the average pain score improved significantly. The overall function score improved only slightly. Results were inferior in the talonavicular arthrodesis. Radiographic evaluation revealed bony union in only 59 percent of the arthrodeses, one third at the talonavicular joint. Secondary degenerative arthritis of the foot and ankle occurred in 107 joints of the 82 feet. Evaluation of dynamic foot pressure measurements revealed an overall prolonged weightbearing on the midfoot region. CONCLUSION: An unacceptably low rate of bony union in some locations, a high incidence of secondary degenerative changes at neighboring joints, and a persistent abnormality of the plantar weightbearing pattern in the operated feet demonstrate unsatisfactory results with the techniques used more than 10 years ago. We now recommend stable internal fixation with optimum adaptation of the bone surfaces of the arthrodesis.

Activities of Daily Living↗
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[Residual placental blood and bone marrow as sources of hematopoietic stem cells for allogenic stem cell transplantation. Comparative analysis of hematopoietic potential].

Umbilical cord blood (UCB) contains a high number of hematopoietic progenitor cells, which can be used for a HLA-identical transplantation. To proof the usefulness of this source of stem cells for transplantation we compared the cellular composition of 19 specimen of bone marrow of healthy donors (BM) and 23 of UCB. We determined the cell number, the frequency of CD34+ progenitor cells and the CFU-GM as well as the T- and B-cell-subsets by means of flow cytometry and in vitro culture methods. The T-cell content was higher in UCB than in BM while the B-cell number was lower. The CD34+ progenitor number per ml was 2.9 fold higher in BM than in UCB, but the frequency and the proliferative capacity of the CFU-GM progenitor cells in the CD34+ population was 8.6 fold higher in UCB than in BM. First clinical trials have demonstrated the usefulness of UCB for allogeneic stem cell transplantation in children. It is possible to harvest 80-100 ml UCB per placenta containing 1.2 x 10(9) nucleated cells with 9.7 x 10(5) (4-15 x 10(5)) CFU-GM.

Adolescent↗
PubMedDate not supplied

Role of extracellular volume expansion in the development of DOC-salt hypertension in the rat.

Changes in inulin space, plasma and blood volume, exchangeable and "noninulin" sodium were studied during the prehypertensive, early and late hypertensive stages of deoxycorticosterone (DOC)-salt administration in the rat. The effect of an acute water load in previously nephrectomized animals was also studied. Hypertension developed after 1 to 2 weeks of the DOC-salt regimen and was always preceded by enlargement of the inulin space and increased plasma and blood volume. Expansion of extracellular fluids receded when blood pressure started to rise but reappeared after 4 to 6 weeks of treatment. Plasma sodium was high only in the hypertensive groups. An acute water load increased blood pressure of normal rats and decreased blood pressure of DOC-salt early hypertensive rats. These findings suggest that extracellular volume expansion inhibits a vasopressor mechanism that involves vasopressin and could be stimulated by hypernatremia.

Animals↗
PubMedDate not supplied

FORMATION OF H-addition radicals in adenine derivatives: part II.

The formation of H-addition radicals in monocrystals of adenosine, adenosine-HCl, adenine-HCl-1/2H2O, and adenine-2 HCl by X-irradiation has been st-died by using electron spin resonance spectroscopy at 9.5 GHz and at 35 GHz. In all crystals, both H-addition radicals at position C2 and at position C8 were observed. The coupling constants of these two H-addition radicals are different and depend strongly on the protonation state of the adenine base. INDO calculations reproduce well the observed trends of the coupling constants. It is shown that the C2-addition radical is transformed into the C8-addition radical by heat and vice versa the C8-addition into the C2-addition by light of lambda greater than 360 nm.

Adenine↗
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Temperature-dependent ESR studies of radical pairs in single crystals of barbituric acid.

After irradiation of single crystals of barbituric acid with X-rays at 77 K different types of radical pairs are found, which are composed of only one type of monoradical. The properties of radical pairs of the unpaired electrons are studied using frequency-variable ESR methods at various temperatures. In addition to the radical pairs AD and BC two further pairs A'D' and XY were identified. Measurements of the fine structure parameter D showed a linear temperature dependence in some regions between 77 K and 290 K. At 240 K the radical pairs AD and A'D' changed reversibly into A*D* and this pair remained stable up to 290 K. A level anticrossing effect was observed with the pair AD. The exchange energy J between the singlet state and the triplet state was determined as -(15.1 +/- 0.6) GHz at 77 K and its temperature coefficient as -(3.8 +/- 0.8) x 10(-3)K-1.

Barbiturates↗
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Structure of adrenodoxin and function in mitochondrial steroid hydroxylation.

The three-dimensional structure of a truncated mutant of bovine adrenodoxin has been resolved at 1.85 A resolution by MAD. The protein consists of a large core region and a more flexible hairpin loop bearing residues which have been previously described as being involved in redox partner recognition. To study the role of distinct protein domains and amino acids of adrenodoxin in interaction with adrenodoxin reductase (AdR), CYP11A1 and CYP11B1, as well as in electron transfer, mutants of adrenodoxin have been prepared by site-directed mutagenesis and produced in Escherichia coli, and their structural and functional properties have been characterized in detail. It could be demonstrated that Tyr82 is located at the edge of the flexible interaction loop of adrenodoxin participating in interactions with AdR and P450s. His56, being close to Tyr82, forms a bridge between the core region of adrenodoxin and the interaction loop. Its role in transmitting changes of the cluster region to the interaction site has also been supported by functional studies. Pro108 of adrenodoxin, the only proline residue contained in the protein and being conserved in this position among several other vertebrate-type ferredoxins, has been demonstrated to be of importance for the correct folding of this protein.

Adrenodoxin↗
PubMedDate not supplied

[Human microsporidiosis].

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AIDS-Related Opportunistic Infections↗