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Biomedical subjects

G Fischer

Publications and source records attributed to G Fischer.

At least 361 records · Page 20Linked to original sources

[Genetics of neurofibromatosis: recent progress and prospects].

Two forms of neurofibromatosis are currently described. Von Reckinghausen Neurofibromatosis (NF 1) is the classic and common form, recently localised to chromosome 17. Neurofibromatosis type 2 (NF 2) or bilateral acoustic Neurofibromatosis, formerly the "central form" of von Reckinghausen disease, is characterized by multiple brain tumors, most often bilateral acoustic neuromas. The NF 2 mutation lies on the long arm of chromosome 22. The two forms predispose to benign or malignant familial tumors, derived from neural crest germ lines, such as Schwann cells. Rapid progress in the understanding of mechanisms underlying neurological tumor formation is expected in these inherited diseases. Molecular biology will allow the precise identification of genes responsible for the neurofibromatose syndromes. Practical applications, such as screening of individuals at risk for the disease will soon be available. Medical follow-up and genetic counselling should improve as a result of these advances.

Genes, Neurofibromatosis 1↗

Slow conformational changes in protein folding can be accelerated by enzymes.

In vitro protein folding is a spontaneous process that is driven by a small difference in Gibbs free energy between the native and unfolded states. The information required for correct folding should be entirely encoded in the amino acid sequence of the protein, although increasing evidence exist that proteins participate in cellular folding events. Isomerization of Xaa-Pro peptide bonds is thought to represent some slow steps of folding kinetics. This type of molecular reorganization have to be important in cellular folding due to the different isomeric states in proteins. Peptidyl-prolyl-cis/trans-isomerase (PPIase) catalyzes some, but not all, proline-limited slow folding reactions. On the other hand, the amino acid sequence of 17,8 kD PPIase from pig kidney is identical with cyclophilin (Cyp) that is the major cellular binding protein for the immunosuppressive drug cyclosporin A (CsA). The connection between enzyme catalyzed cis/trans isomerization, protein folding and immunosuppression is still unknown. PPIases of the cyclophilin type are found in most organisms and in various subcellular compartments. Recently a second family of PPIases has been discovered. These small proteins are structurally related to the cyclophilins; yet they bind with a high affinity to another immunosuppressive drug, the macrolide FK 506. Although it seems to be logical to ascribe the enzymatic activity of these proteins to a catalytic role in the folding of proteins within the cell other possibilities must also be considered and are discussed.

Amino Acid Isomerases↗

Endogenous nitrate synthesis in selected infectious diseases and ulcerative colitis.

Investigations into acute and chronic diarrheal patients confirmed the results of animal experiments on the role of cytotoxic activated macrophages in endogenous formation of nitrates. Because a number of inflammatory diseases did not cause a nitrate release in urine, blood, and saliva, the general importance of nitrates to characterize the initiation and course of inflammations must be questioned.

Colitis, Ulcerative↗

[Meningioma of the apex of the tentorial incisura. Diagnostic and surgical aspects apropos of a series of 7 cases].

Seven cases of meningiomas implanted on the medial portion of the free edge of the tentorium are reported. The denomination "meningiomas of the apex of the tentorial incisura" is proposed. In 4 patients, the clinical presentation was that of an intracranial hypertension without signs of compression of the quadrigeminal plate involvement. In the other 3 patients, the initial symptoms were those of the triad of the adult chronic hydrocephalus (N.P.H.) syndrome. Angiographic evaluation provides useful informations on the arterial supply (which is mainly from the tentorial branches of the internal carotid arteries and occasionally from the middle meningeal arteries) and the relationships of the tumor with the deep venous system. C.T. and M.R.I. facilitate earlier diagnosis and better demonstration of implantation and extension of the tumor, which the selection of a surgical approach is based upon. Four patients have undergone an occipital supratentorial approach and 2 a supra-cerebellar infra-tentorial approach. The meningioma was totally removed in 5 patients, sub-totally in 1 to avoid bilateral lesions of the visual pathways and cortical areas. The 7th patient was treated by C.S.F. shunt alone. No operative mortality occurred. The follow-up is averaging 18 months: 4 patients are symptom-free, 3 exhibit minor sequelae (epilepsy: 1, visual field defects: 2, memory impairement: 2). Six patients of the series have resumed their previous activities. Discussion is focused on the difficulties of surgical removal of this particular type of tentorial meningioma, resulting from volume, implantation and relationships of the tumor with the deep veins.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

Serotonin organelles of rabbit platelets contain synaptophysin.

Synaptophysin, an integral membrane protein of synaptic vesicles in nerve terminals and a class of small translucent vesicles in neuroendocrine cells, was detected in intact rabbit platelets by immunoblotting, immunofluorescence staining and immuno-electron microscopy. In a highly purified preparation of serotonin organelles isolated from rabbit platelets, synaptophysin was enriched approximately 10-15-fold over platelet homogenate. About 80% of total platelet synaptophysin was present in this purified fraction. The apparent molecular mass (approximately 38 kDa) and the extent of glycosylation of platelet-derived synaptophysin was more similar to the neuronal than to the neuroendocrine form of the protein. Immunofluorescence microscopy revealed that synaptophysin was compartmentalized in intact rabbit platelets and immuno-electron microscopy of subcellular fractions showed that it was localized exclusively to the membrane surface of serotonin organelles. No synaptophysin-like immunoreactivity was detected in platelets from other species such as human, guinea pig and rat. Another integral membrane protein of synaptic vesicles, p65, and a family of synaptic vesicle-associated phosphoproteins, the synapsins, were not detected in platelets of any species tested. These results provide evidence that serotonin organelles from rabbit platelets share a subset of protein components with synaptic vesicles from neurons. Synaptophysin in serotonin organelles from rabbit platelets, as suggested for small synaptic vesicles in neurons, might play a role in the formation of protein channels for the exocytotic release of serotonin.

Animals↗

[Usefulness and cogency of gene probes in paternity questions (Personal experiences: 1989/90].

In cases of disputed parentage usually more than 20 polymorphic systems (red and white cell antigens, serum markers and enzyme markers) have to be analyzed using a battery of different techniques. A more recent method involving analysis of restriction fragment length polymorphism in highly polymorphic genes allows assignment of offspring to their parents. To test the latter method, 28 paternity cases were studied in parallel using conventional systems and detection of RFLPs of probes MS 1, MS 31, MS 43, and g 3, developed by Jeffreys et al. Furthermore, the cogency of exclusion of parentage, the average power of exclusion and the probability of parentage is calculated using published mutation rates and gene frequencies of the four probes. In conclusion, use of the four gene probes has both theoretically and practically turned out to be a powerful method for parentage testing.

Blood Group Antigens↗

[Cardiovascular pharmacology. An example of the need of clinically relevant pharmacological research].

Like all other scientific disciplines, preclinical pharmacological research is subject to permanent changes. New measuring devices and the possibility of continuous on line data acquisition have markedly influenced basic research in this field. Another aim of modern cardiovascular pharmacology is the testing of promising drugs in clinically relevant animal models of disease, particularly under conditions, referring to the everyday situation in patients, e.g. physical activity. Investigations carried out in this way allow an exact assessment of the clinical efficacy of new drugs, and are, thus, clearly indispensable, also from the ethical point of view, before primary evaluation of the drug in man.

Angina Pectoris↗

Purification of soluble guanylyl cyclase from bovine lung by a new immunoaffinity chromatographic method.

Soluble guanylyl cyclase was purified from bovine lung by an immunoaffinity chromatographic method using IgG fractions of antisera against a synthetic peptide of the C-terminus of the 70-kDa subunit of the enzyme. After anion-exchange chromatography, the enzyme was bound to an immunoaffinity column and was eluted with the synthetic peptide. This method allowed the convenient isolation of 2 mg of apparently homogeneous enzyme from 40 g cytosolic proteins. The enzyme had an apparent molecular mass of about 150 kDa and consisted of two subunits (70 kDa and 73 kDa) as determined by gel permeation fast protein liquid chromatography and SDS/PAGE. The basal activities determined in the presence of Mg2+ and Mn2+ were 10-20 nmol.min-1.mg-1 and 80-100 nmol.min-1.mg-1, respectively. The enzyme exhibited an ultraviolet-visible absorption spectrum typical for hemoproteins, with a Soret band at 430 nm. The purified enzyme was stimulated by NO-containing compounds. Maximal enzyme activities measured in the presence of sodium nitroprusside were 1.2-2.4 mumol.min-1.mg-1 (half-maximal effect of sodium nitroprusside at 1.3-1.9 microM) and 0.9-1.8 mumol.min-1.mg-1 (half-maximal effect at 0.28-0.41 microM sodium nitroprusside) in the presence of Mg2+ and Mn2+, respectively. The method developed for the large-scale purification of soluble guanylyl cyclase by immunoaffinity chromatography, using synthetic peptides for the elution of the enzyme, appears to be superior to previously described methods. As antibodies against synthetic peptides corresponding to deduced amino acid sequences of the respective protein are easily obtained, the described method may be suitable for a convenient large-scale purification of various proteins.

Animals↗

[Assessment of apparent non-maternity using individual specific gene probes].

In a case of disputed paternity mother and child showed a genetic incompatibility in the Kidd system of the erythrocytes: mother Jk(a-b+), child Jk (a+b-). For the first time the RFLP technique solved this problem, using four different Jeffreys' highly polymorphic single locus DNA probes MS 1, MS 31, g 3 and MS 43. We found that mother and child possessed one identical gene observed in each of the four probes. The confidence of somatic genuineness of this mother-child pair is very strong: p = 10(9). In addition, the above-mentioned four DNA probes showed identical results in 12 cases of paternity exclusion and 18 nonexclusions found by 23 conventional hereditary systems. Furthermore, in five cases of bone marrow transplantation success of this therapy was proven by the RFLP technique, which differentiates between recipient genes and donor genes. Our investigations on hereditary so far comprise five families with 10 children and one family over four generations.

Blood Group Antigens↗

Haemodynamic and metabolic effects of xamoterol in exercising dogs.

The effects of xamoterol on the haemodynamic adaptation to graded treadmill exercise were evaluated during five subsequent cycles in chronically instrumented dogs. At rest xamoterol, 0.2 mg/kg i.v., preferentially showed a positive inotropic effect, whereas 1 mg/kg i.v. also exhibited a marked chronotropic effect. The cardiac output and left ventricular power increased dose dependently. The mean left atrial pressure and total peripheral resistance decreased concomitantly. Xamoterol did not produce a noteworthy decrease in heart rate or positive dp/dtmax during exercise, even at a dosage of 1 mg/kg. A beta-adrenoceptor blocking effect could only be seen from the diminution of the exercise-induced changes in heart rate, dp/dtmax, cardiac output, left ventricular power and total peripheral resistance. Determination of the blood glucose, lactate and pyruvate levels before the start of each exercise cycle revealed that the drug induced a decrease in blood glucose and an increase in blood pyruvate. Thus, xamoterol exerted a dose-dependent sympathomimetic effect in dogs at rest. However, there was little evidence for a beta-adrenoceptor blocking action even at higher work loads, although preliminary experiments in conscious dogs showed that xamoterol shifted the isoprenaline dose-response curve to the right by a factor of 1.31 (0.2 mg/kg) and 3.05 (1 mg/kg).

Animals↗

Cardiovascular effects of flesinoxan in anaesthetized and conscious dogs.

Stimulation of 5-HT1A receptors is known to decrease the arterial blood pressure in anaesthetized rats, cats and dogs. We investigated the hypotensive activity of flesinoxan (0.1 + 0.2 + 0.7 mumol/kg), a 5-HT1A-receptor agonist, in dogs anaesthetized with either morphine and pentobarbital or enflurane and also in the conscious state. Flesinoxan led to a decrease in arterial blood pressure in anaesthetized, but not in conscious dogs. In the conscious state the marked increase in heart rate, which can be taken as an indicator of sympathetic tone, may have masked the consequences of vasodilatation. These different haemodynamic responses to flesinoxan may be dependent on side effects of the drug in the conscious dogs, in particular hyperventilation and salivation combined with anxiety, and on the magnitude of the decrease in baroreceptor reflex activity during anaesthesia with morphine and pentobarbital on the one hand and enflurane on the other hand.

Anesthesia↗

[Acetabular fractures--surgical versus conservative treatment].

In this paper the results of operative and conservative intervention of acetabulum fractures are analysed. It was possible to re-examine 80 of 146 Patients after a period of 5.46 years in mean. 23 patients were treated by osteosynthesis. Time from accident to operation was 13 days in mean. Posterior wall fractures seemed to be the most frequent (classified by Letournel). Results were evaluated according to the following criteria: clinical status (classified by the scheme of Merle d'Aubigne), X-ray, and subjective well-being. In the surgically treated group total hip prosthesis had to be implanted in five patients because of aseptic necrosis of the femoral head, 52.9% of the patients in this group had good results. In the conservative treated cases no total hip prosthesis had to be implanted. 77.8% of the patients had good results. A main aspect is that the average age of the patients who underwent a treatment by osteosynthesis is lower although the fractures were more severe.

Acetabulum↗

Verification of a canine model of transient exercise induced myocardial dysfunction: antianginal effects of flestolol, an ultra short acting beta adrenoceptor antagonist.

STUDY OBJECTIVE - The aim of the study was to verify the reproducibility of a canine model of treadmill exercise induced regional myocardial dysfunction designed to mimic exertional angina pectoris in man. DESIGN - Dogs trained to run on a treadmill were chronically instrumented with a microtip manometer in the left ventricle, a hydraulic occluder around the circumflex branch of the left coronary artery, two pairs of crystals for sonomicrometry, and arterial and venous catheters. Experiments were started 10 d after surgery, when the animals were submitted to seven treadmill exercise cycles, each of 3 min, with a 7 min recovery period. Ischaemia was adjusted so as not to impair regional function at rest but to produce progressive dysfunction with increasing work load. Flestolol (1 microgram.kg-1.min-1) was infused intravenously during the third and fourth exercise cycle. SUBJECTS - Six mongrel dogs, 13.5-29.5 kg, were used. MEASUREMENTS and RESULTS - Flestolol caused a marked reduction in the exercise induced increase in left ventricular positive dP/dtmax, and minor reductions in heart rate and systolic blood pressure, resulting in a decrease in myocardial oxygen demand and an improvement in regional function in the circumflex area of the left coronary artery. The functional improvement was transient and disappeared entirely after termination of flestolol infusion. CONCLUSIONS - The results show that flestolol is beneficial in conditions of limited coronary reserve and exercise induced myocardial dysfunction. The fact that the extent of regional myocardial dysfunction was comparable before and after flestolol infusion confirms the stability and usefulness of this experimental model in the evaluation of antianginal drugs.

Adrenergic beta-Antagonists↗

Effects of flestolol, an ultra-short acting beta-adrenoceptor antagonist, on hemodynamic changes produced by treadmill exercise or isoprenaline stimulation in conscious dogs.

The beta-blocking activity of flestolol was established during increasing isoprenaline infusions and during graded physical exercise in conscious, chronically instrumented dogs. After a control cycle, flestolol was infused at three doses (1, 2.67, and 10 micrograms/kg/min). Flestolol has an extremely short half-life, demonstrated by an 83% loss of effect within 25 min. Thus, flestolol allows easy titration of the effect, which might be a valuable property for its use in the treatment of critically ill patients. Due to the difference between pure beta-adrenergic stimulation and the much more complex regulation of circulation during exercise, the hemodynamic response to flestolol elicited marked differences between both set ups. Flestolol shifted the dose-response curves of isoprenaline-induced changes in heart rate, positive left ventricular dp/dtmax, and diastolic arterial pressure dose dependently to the right, while its main effect during exercise was a decrease in positive left ventricular dP/dtmax. Thus, testing of beta-adrenoceptor blockers using isoprenaline-induced tachycardia leads to an overestimation of potency and therefore is not appropriate to predict the clinical efficacy of these drugs to prevent stress- or exercise-induced increases in heart rate and hence myocardial oxygen-demand.

Adrenergic beta-Antagonists↗

Cardiac and hemodynamic effects of diltiazem during exercise-induced myocardial dysfunction in dogs.

The effects of diltiazem were tested in chronically instrumented dogs in a model of exercise-induced myocardial dysfunction. Since various bradycardiac agents have beneficial effects on myocardial function during ischemia, it was of interest to find out how a decrease in afterload, possibly combined with a decrease in myocardial oxygen demand, influences dysfunction. Therefore, diltiazem (1 mg/kg i.v.) was tested during critical stenosis of the circumflex branch of the left coronary artery, which led to exercise-induced myocardial dysfunction. At rest, diltiazem causes a reflex increase in heart rate. During exercise, a decrease in heart rate and hence in myocardial oxygen demand was neutralized by a decrease in arterial blood pressure and hence a lowered myocardial perfusion pressure. Therefore, systolic shortening in the ischemic area improved neither at rest nor during exercise after diltiazem.

Angina Pectoris↗