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Biomedical subjects

M Walter

Publications and source records attributed to M Walter.

At least 19 recordsLinked to original sources
PubMed1992

Activation of maternal centrosomes in unfertilized sea urchin eggs.

Centrosomes are undetectable in unfertilized sea urchin eggs, and normally the sperm introduces the cell's microtubule-organizing center (MTOC) at fertilization. However, artificial activation or parthenogenesis triggers microtubule assembly in the unfertilized egg, and this study explores the reappearance and behavior of the maternal centrosome. During activation with A23187 or ammonia, microtubules appear first at the cortex; centrosomal antigen is detected diffusely throughout the entire cytoplasm. Later, the centrosome becomes more distinct and organizes a radial microtubule shell, and eventually a compact centrosome at the egg center organizes a monaster. In these activated eggs, centrosomes undergo cycles of compaction and decompaction in synchrony with the chromatin, which also undergoes cycles of condensation and decondensation. Parthenogenetic activation with heavy water (50% D2O) or the microtubule-stabilizing drug taxol (10 microM) induces numerous centrosomal foci in the unfertilized sea urchin egg. Within 15 min after incubation in D2O, numerous fine centrosomal foci are detected, and they organize a connected network of numerous asters which fill the entire egg. Taxol induces over 100 centrosomal foci by 15 min after treatment, which organize a corresponding number of asters. The centrosomal material in either D2O- or taxol-treated eggs aggregates with time to form fewer but denser foci, resulting in fewer and larger asters. Fertilization of eggs pretreated with either D2O or taxol shows that the paternal centrosome is dominant over the maternal centrosome. The centrosomal material gradually becomes associated with the enlarged sperm aster. These experiments demonstrate that maternal centrosomal material is present in the unfertilized egg, likely as dispersed undetectable material, which can be activated without paternal contributions. At fertilization, paternal centrosomes become dominant over the maternal centrosomal material.

Ammonia↗
PubMed1992

[Spieghel hernia--a rare cause of acute abdomen].

Spieghelian hernia is a rare rupture of the abdominal wall along the linea semilunaris. Due to the fact that the rupture is overlain by the aponeurosis of M. externus abdominis, it is often not recognized in its early stage. In most cases the rupture neck is mostly very narrow and in 24.1% of all cases an incarceration of intestinal parts has ensued which may even lead to the development of an acute abdomen. The first choice therapy will consist in an operative support including the reposition of the hernial content and a possible resection of ischaemic organs as well as removal and sealing of the hernia. Because of the rarity of this sickness we report on a patient in our clinic who was operated as an emergency.

Abdomen, Acute↗
PubMed1992

A new vascular prosthesis of bovine origin.

An experimental study on a new biologic vascular graft for reconstruction of small diameter arteries was carried out in 50 sheep. A follow-up period of two years let us conclude that the new vascular prosthesis may be "re-utilized" by the host. Infection and aneurysmatic degeneration could not be observed. An early occlusion of the graft occurred in only one case, due to technical reasons.

Anastomosis, Surgical↗
PubMed1992

Hepatitis B virus p25 precore protein accumulates in Xenopus oocytes as an untranslocated phosphoprotein with an uncleaved signal peptide.

We have analyzed the translocation of hepatitis B virus (HBV) precore (PC) proteins by using Xenopus oocytes injected with a synthetic PC mRNA. The PC region is a 29-amino-acid sequence that precedes the 21.5-kDa HBV capsid or core (C) protein (p21.5) and directs the secretion of core-related proteins. The first 19 PC amino acids provide a signal peptide that is cleaved with the resultant translocation of a 22.5-kDa species (p22.5), in which the last 10 PC residues precede the complete p21.5 C polypeptide. Most p22.5 is matured to 16-20 kDa species by carboxyl-terminal proteolytic cleavage prior to secretion. Here we show that some four unexpected PC proteins of 24 to 25 kDa are produced in addition to the secretion products described above. Protease protection and membrane cosedimentation experiments reveal that all PC proteins behave as expected for proteins that are translocated into the lumen of the endoplasmic reticulum except for the single largest PC protein (p25), which is not translocated. Like p21.5, p25 is a phosphoprotein that localizes to the oocyte cytosol and nucleus, and protease digestion studies suggest that the two molecules have similar two-domain structures. Radiosequencing of immobilized p25 demonstrates that it contains the intact PC signal peptide and represents the unprocessed translation product of the entire PC/C locus. Thus, while many HBV PC protein molecules are correctly targeted to intracellular membranes and translocated, a significant fraction of these molecules can evade translocation and processing.

Amino Acid Sequence↗
PubMed1992

[Ergotism and ischemia of the limbs].

Clinical ergotism as seen today results almost exclusively from the intake of ergotamine tartrate in the treatment of migraine headache. Vasospasm of peripheral arteries is the leading clinical picture. Besides the formation of collaterals and a secondary thrombosis, the vasospasm is one of the specific findings in arteriography. Early diagnosis and withdrawal of the medication makes complete restitution possible. In all other cases intraarterial or intravenous infusion of sodium nitroprusside has turned out to be the most effective therapy. Balloon dilatation or operative intervention are an alternative therapy in those cases, where amputation of the limbs seems to be necessary.

Adult↗
PubMed1992

[The compartment syndrome with special reference to vascular surgery aspects. A patient sample of the Cologne University Clinic 1981 to 1991].

The compartment syndrome, a well known complication in traumatized patients, is not taken enough notice of in the literature of vascular surgery despite it's obviously important pathophysiological context. Considering arterial occlusive disease the ischemia as well as the reperfusion can increase the compartmental volume respectively the tissue pressure. The subfascial pressure measurement should not lead to a false certainty, since no critical pressure values exist that can serve as a general criterion for diagnosis and treatment. The "thought about it" may be the first step to a clinical diagnosis and subsequent therapy. Decompression of all four compartments at the lower leg by the technique of Matsen represents the therapy of choice for the compartment syndrome of the lower leg.

Adolescent↗
PubMed1992

[Mandibular positions in complete dentures according to the calotte principle].

A total of 37 patients was provided with complete dentures according to the calotte system. Two groups were formed with regard to the arrangement of the anterior teeth. After a mean period of wear amounting to 13 months different positions of the mandible were recorded in 21 patients under the guidance of a central bearing point and in occlusion. Patients with an arrangement of the anterior teeth free of interferences in excursive movements exhibited a significantly lower distance habitual occlusion/retruded position than subjects with an overlap limiting sagittal freedom. Therefore, an arrangement of the anterior teeth integrated into the calotte complex respectively free of interferences in eccentric positions is to be preferred.

Dental Articulators↗
PubMed1992

Influence of upright exercise on pulmonary hemodynamics in left heart failure.

Studies in severe chronic stable heart failure (HF) indicate that pulmonary resistance might remain unchanged during exercise and could subsequently contribute to limitation in exercise capacity of these patients. We assessed the possible role of the exercise decreases in mixed venous oxygen tension on this phenomenon in fifteen patients with chronic congestive heart failure (N.Y.H.A. functional classes II to IV) who underwent a symptom-limited treadmill exercise test with hemodynamic monitoring as well as repeated arterial and mixed venous blood gas analysis. For all patients there was an increase in cardiac output (from 3.7 +/- 0.2 to 6.7 +/- 0.5 l/min, p less than 0.001) and pulmonary wedge pressure (from 16 +/- 2 to 31 +/- 3 mm Hg, p less than 0.001) along with exercise with highly significant decrease in total systemic resistance and no significant (from 25.6 +/- 1.5 to 15.8 +/- 1.0 U, p less than 0.001) changes in pulmonary vascular resistances. Arterial blood oxygen tension increased from 86 +/- 3 to 99 +/- 3 mm Hg (p less than 0.001) and mixed venous oxygen tension (PvO2) decreased from 33 +/- 1 to 22 +/- 1 mm Hg (p less than 0.001). Changes in pulmonary vascular resistance during exercise were inversely related to changes in PvO2 (r = -0.61; p less than 0.05). We conclude that the observed decrease in PvO2 might be a determinant of unchanged pulmonary vascular resistance during treadmill-exercise test in severe heart failure patients.

Adult↗
PubMed1991

[Surgical therapy of bronchial cancer. Healing or palliation?].

In spite of the revolutionary innovations concerning diagnostic and intensive care techniques as well as better understanding of tumour biology during the last decade, rates of resection and long-term survival in bronchogenic carcinoma could not be improved. Nevertheless there is no reason for therapeutic nihilism. On the contrary all efforts are to be done in investigation on practicable, suitable, and supportable screening programmes to improve the patients outcome.

Carcinoma, Bronchogenic↗
PubMed1991

Site-specific methionine sulfoxide formation is the structural basis of chromatographic heterogeneity of apolipoproteins A-I, C-II, and C-III.

ApoA-I and apoC-II are eluted in two isoforms and apoC-III2 is eluted in three isoforms by reversed phase high performance liquid chromatography (HPLC). The structural basis of these nongenetic heterogeneities was unravelled using HPLC of proteolytic peptides and time-of-flight secondary ion mass spectrometry (TOF-SIMS). In apoA-I, the chromatographic microheterogeneity was caused by the formation of methionine sulfoxides (MetSO). However, only residues Met112 and Met148 were found oxidized, whereas Met86 was unaffected and also resistant towards artificial oxidation. To assess whether and to what extent amino acid substitutions in apoA-I might affect methionine sulfoxidation, the tryptic peptides of 13 different mutant apoA-I proteins from 24 heterozygous apoA-I variant carriers were analyzed by HPLC. In normal apoA-I, the ratios MetSO112/Met112 and MetSO148/Met148 were highly variable. By contrast, the relative ratio of oxidation of methionine residues 112 and 148 was constant. The amino acid changes Lys107----Met, Lys107----O, Glu139----Gly, Glu147----Val, and Pro165----Arg resulted in the preferential oxidation of Met112, and Asp103----Asn resulted in a preferential oxidation of Met148; whereas Pro3----Arg, Pro3----His, Pro4----Arg, Asp89----Glu, Ala158----Asp, Glu198----Lys, and Asp213----Gly had no impact. ApoC-II and apoC-III isoforms differed by the oxidation of the two methionine residues in these proteins. Whereas in apoC-II both methionine residues were oxidized in parallel, in apoC-III the two methionine residues differed in their susceptibility towards oxidation. We conclude that the formation of MetSO depends on the molecular microenvironment within a protein.

Amino Acid Sequence↗
PubMed1991

[Primary and secondary aorto-intestinal fistula in infrarenal aortic replacement].

During the past 20 years 17 patients with abdominal-aortic-intestinal fistulas have been operated in our department. Hospital-letality accounted till 1986 with 75%. Since then we preferred direct reconstruction by implantation of a vascular graft, covered by omentum in primary fistulas. Hospital letality could be reduced by this management to 0% in primary fistulas by a total survival rate of 67%.

Aorta, Abdominal↗
PubMed1991

[A new biological vascular prosthesis].

In an experimental study on sheeps a new biologic vascular graft was implanted, 30 x in carotidal, 30 x in aortal position. Only one early occlusion of the graft, due to technical reasons, could be observed. Without aneurysmatic degeneration all graft were in function at the time of harvesting the samples. Morphologically a "revitalisation" of the grafts could be proved.

Animals↗
PubMed1991

[Is titanium an alternative for base metal alloys?].

Because of the excellent biocompatibility titanium can be considered as an ideal material for prosthetic reconstructions. Especially for base metal alloys titanium is an alternative due to the low cost. Processing still causes problems. In this paper a vacuum pressure casting system and a combination of milling and spark erosion are described and investigated. Both techniques are suitable to manufacture prosthetic restorations with a high accuracy of fit. Problems in dental castings lie in the occurrence of a superficial reaction zone of about 40-100 microns width. No final conclusions concerning the metal-ceramic compound can be drawn at the moment for lack of undisputable results in different mechanical bonding tests. Due to the remaining difficulties the future importance of titanium in prosthetic dentistry cannot be prognosticated.

Dental Alloys↗
PubMed1991

[Castability and accuracy of fit of a titanium casting system].

The titanium casting system Cyclarc (Morita) was examined for its suitability for the fabrication of dense, fitting restorations. The investment material Titavest CB exhibited no setting expansion. Instead, thermal expansion, highly dependent on the liquid/power ratio and the temperature during preheating, was observed. The castability of unalloyed titanium is fully acceptable for the fabrication of prosthetic restorations. Single crowns showed a high accuracy of fit, if an optimal liquid/power ratio was used for investment.

Crowns↗
PubMed1991

[Ceramo-metallic bond of cast titanium].

The ceramo-metallic bond strength of cast titanium was tested according to DIN draft 13927. While the specimens failed in the bending tests, they clearly passed the 3-point bending test after removal of the surface reaction layer prior to firing. Light microscopy and SEM showed a satisfactory wetting of the titanium surface by the ceramic material. The result of X-ray analyses suggest that titanium particles are retained in the ceramic material when this layer is broken off its metallic substructure.

Dental Bonding↗
PubMed1991

[Fixed tooth replacement of milled/spark eroded titanium].

In a clinical study the accuracy of fit of 82 crowns manufactured with the Procera-system (duplication milling/spark erosion) was investigated. The average marginal space width was 71 microns. Roughness of eroded surfaces was found to be similar to that of coarsely ground metal. Below the eroded areas a zone of increased hardness with a width of approximately 20 microns was demonstrated.

Crowns↗