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Biomedical subjects

A Riedel

Publications and source records attributed to A Riedel.

At least 37 records · Page 2Linked to original sources
PubMed1995

EPR, electron spin echo envelope modulation, and electron nuclear double resonance studies of the 2Fe2S centers of the 2-halobenzoate 1,2-dioxygenase from Burkholderia (Pseudomonas) cepacia 2CBS.

The 2-halobenzoate 1,2-dioxygenase from Burkholderia (Pseudomonas) cepacia 2CBS (Fetzner, S., Müller, R., and Lingens, F. (1992) J. Bacteriol. 174, 279-290) contains both a ferredoxin-type and a Rieske-type 2Fe2S center. These two significantly different 2Fe2S clusters were characterized with respect to their EPR spectra, electrochemical properties (Rieske-type cluster with gz = 2.025, gy = 1.91, gx = 1.79, gav = 1.91, Em = -125 +/- 10 mV; ferredoxin-type center with gz = 2.05, gy = 1.96, gx = 1.89, gav = 1.97, Em = -200 +/- 10 mV) and pH dependence thereof. X band electron spin echo envelope modulation and electron nuclear double resonance spectroscopy was applied to study the interaction of the Rieske-type center of the 2-halobenzoate 1,2-dioxygenase with 14N and 1H nuclei in the vicinity of the 2Fe2S cluster. The results are compared to those obtained on the Rieske protein of the cytochrome b6f complex (Em = +320 mV) and the water-soluble ferredoxin (Em = -430 mV) of spinach chloroplasts, as typical representatives of the gav = 1.91 and gav = 1.96 class of 2Fe2S centers. Properties common to all Rieske-type clusters and those restricted to the respective centers in bacterial oxygenases are discussed.

Burkholderia cepacia↗
PubMed1995

The 2Fe2S centres of the 2-oxo-1,2-dihydroquinoline 8-monooxygenase from Pseudomonas putida 86 studied by EPR spectroscopy.

The 2-oxo-1,2-dihydroquinoline 8-monooxygenase from Pseudomonas putida 86 comprises two components with four redox active sites necessary for activity. We present an EPR characterization of the iron-sulfur centres in the purified reductase and oxygenase component of this novel enzyme system. The oxygenase component was identified as a Rieske [2Fe2S] protein on the basis of its characteristic EPR spectrum with gz,y,x = 2.01, 1.91, 1.76 and gav = 1.893. The reductase component, an iron-sulfur flavoprotein, contained a [2Fe2S] cluster with gz,y,x = 2.03, 1.94, 1.89 and the average g-value (gav) of 1.953, typical of a ferredoxin-type centre. In redox titrations at pH 7, the midpoint potentials were determined to be -180 mV +/- 30 mV and -100 mV +/- 10 mV for the reductase and oxygenase component, respectively. A detailed comparison to other multicomponent enzyme systems is presented pointing out the EPR and redox properties of the FeS centres involved.

Electron Spin Resonance Spectroscopy↗
PubMed1993

[Follow-up studies of patients with negative TRH test and normal thyroid hormone levels].

The aim of the study was to assess the clinical significance of the association of a negative TRH-test with normal thyroid hormone levels. Therefore, we repeated the investigation in 63 patients one year after the first examination. In 6 patients (10%) hyperthyroidism had developed. Euthyroid autonomy was diagnosed in 11 patients (17%). A prolonged normalisation period of the pituitary-thyroid regulation after having discontinued the thyroid hormone drugs was found in 7 patients (11%). In 40% of the patients the TRH-test remained negative and in 22% of the patients the TSH-response became positive without any known reason. The findings show that a negative TRH-test and normal thyroid hormone levels do not necessarily imply subclinical hyperthyroidism.

Adult↗
PubMed1992

The Rieske FeS center from the gram-positive bacterium PS3 and its interaction with the menaquinone pool studied by EPR.

The Rieske 2Fe2S center from Bacillus PS3, a Gram-positive thermophilic eubacterium, has been studied by EPR spectroscopy. Its redox midpoint potential at pH 7.0 was determined to be +165 +/- 10 mV and was found to decrease with an apparent slope of -80 mV/pH unit above pH 7.9. The Qo-site inhibitor stigmatellin induced spectral changes analogous to those reported for Rieske centers from mitochondria and chloroplasts. The redox midpoint potential of the PS3 Rieske cluster was not affected by stigmatellin. The orientation of the g tensor was similar to other Rieske centers (gz and gy are oriented parallel, gx is oriented perpendicular to the membrane plane). The shape of the EPR spectrum of the Rieske cluster from PS3 changed as a function of the redox state of the menaquinone (MK) pool. This permitted the redox midpoint potential of the MK pool to be determined in the membrane. Values of -60 +/- 20 mV at pH 7.0 and of -130 +/- 20 mV at pH 8.0 were obtained. The results are compared with already published data from other Rieske centers. It is proposed that all Rieske centers that function in electron transport chains using MK as pool quinone show common features that distinguish them from Rieske centers operating in ubiquinone- or plastoquinone-based electron transfer chains.

Anti-Bacterial Agents↗
PubMed1992

Effect of BN 52256 and other mediator antagonists on ouabain-induced ventricular fibrillation in sensitized guinea-pigs and on ischemia-induced fibrillation in rats.

The threshold dose of ouabain necessary to induce ventricular fibrillation is decreased in sensitized guinea-pigs signalizing an enhanced arrhythmogenicity. Esculetine or WEB 2170 antagonists of histamine and PAF, respectively and especially a combination of both can increase the threshold dose of ouabain-induced fibrillation demonstrating an antiarrhythmic effect. BN 52256 a substance with multi-antagonistic properties shows antiarrhythmic effect in this method, too. WEB 2170 and BN 52256 decrease the incidence of ventricular fibrillation after coronary ligation in rats.

Anesthesia↗
PubMed1991

Chloroplast Rieske Center. EPR study on its spectral characteristics, relaxation and orientation properties.

The spectral parameters, the orientation of the g tensor in two-dimensionally ordered multilayers and the relaxation properties of the Rieske center in purified cytochrome b6f complex from spinach were studied by EPR spectroscopy. A trough at g = 1.76 - 1.74 was unambiguously identified as the gx signal on the basis of the sensitivity of its field position to inhibitors and oxidized plastoquinone. In contrast to previous reports, the orientation of the chloroplast Rieske center was found to be identical to that of its cytochrome bc1 counterpart, provided that non-saturating EPR conditions were applied. Upon onset of microwave saturation, however, the orientation with respect to the ordered multilayers where the gy signal (g = 1.9) was maximal, changed drastically and was then similar to the orientation reported previously (Prince R. C., Crowder, M. S., and Bearden, A. J. (1980) Biochim. Biophys. Acta 592, 323-337). The unusually anisotropic saturation behavior of the EPR spectrum was characterized in detail, whereby hitherto controversial results on the spectral parameters of the chloroplast Rieske center could be rationalized. The observed phenomena are discussed on the basis of three tentative models which are able to qualitatively explain the effects.

Chloroplasts↗
PubMed1991

Morphometric study on the postnatal growth of the hippocampus in Australian Aborigines and Caucasians.

In an autopsy study on Australian Aborigines (29 males, 27 females) and Caucasians (57 males, 37 females) the postnatal growth of the hippocampus was studied and described by mathematical growth functions. For male adults no significant difference in hippocampal volume was found. In contrast, hippocampal volume was significantly smaller for Aboriginal females compared to Caucasian females. Growth analysis showed slower growth rates and later half-value times for Aborigines compared to Caucasians. These results are discussed in relation to secular changes of growth parameters of the human brain during the last century, the socioeconomic and health status of Aborigines, and sexual differences in development and plasticity of the hippocampus.

Adolescent↗
PubMed1991

Quantitative changes during the postnatal maturation of the human visual cortex.

Postnatal development of the human visual cortex is characterized by an overshooting growth pattern of its volume with a maximum at 8 postnatal months and by loss of a substantial proportion of its neurons. The highest rate of reduction in neuronal numbers is observed in layers II-IVa, with other layers showing a more gradual postnatal decrease.

Adolescent↗
PubMed1991

[Three-dimensional reconstructions in neuroanatomy].

Computer-aided 3D reconstructions of neurofunctional systems and structures are generated as a reference for neuroimaging (CT, MRI, PET). The clinical application of these 3D reconstructions requires a coordinate system and conditions resembling the intravital neuroanatomy as far as possible. In this paper the neuroanatomical Reference System (NeuRef) of the Department of Neuroanatomy of Hannover Medical School is presented. This consists of methods to record brain structures from serial sections with minimal error (less than 1 mm) and to display 3D brain models derived from such a data base. In addition, NeuRef is able to generate sections through, for instance, the visual and pyramidal system and to transfer these data onto a corresponding CT image. Therefore, this method can serve as a diagnostic aid in neuroradiology, in operation planning, and radiotherapy. It can also be used in PACS.

Brain↗
PubMed1989

Morphometric study on the postnatal growth of the cerebellum of Australian aborigines and Caucasians.

In an autopsy study on 29 male Aborigines and 57 male Caucasians, macroscopic and microscopic parameters of postnatal cerebellar development were determined and described by mathematic growth functions. For the whole cerebellum and its cortical layers volume measurements revealed delayed maturation for Aborigines compared to Caucasians. Despite the slower development in childhood, significantly smaller values for adult Aborigines compared to Caucasians were observed only for the whole cerebellum and the Purkinje cell sheet. Similarly, postnatal changes in Purkinje cell size showed prolonged growth phases in Aborigines compared to Caucasians. Calculations of absolute cell numbers for individual layers demonstrated later half-value times and slower growth rates for cell numbers in the internal granular and molecular layers consistent with the findings for the corresponding layer volumes. For Caucasians, the growth curve for the absolute cell number in the internal granular layer showed a maximum about 21 months postnatally and subsequently decreased towards adulthood by about 18%. No such overshoot could be demonstrated for Aborigines. In relation to absolute cell numbers in adulthood, this could indicate a smaller number of granule cells migrating from the external to the internal granular layer as well as less pronounced granule cell death in Aborigines compared to Caucasians. The external granular layer of Caucasians increased in volume postnatally to reach a maximum at about 4 months and subsequently decreased until its disappearance at approximately 2 years of age. The number Purkinje cells decreased marginally postnatally in both populations. These results were discussed in relation to secular changes of growth parameters of the cerebellum during the last century and the socioeconomic and health status of Aborigines.

Adolescent↗
PubMed1989

Morphometric study on the postnatal growth of non-cortical brain regions in Australian aborigines and Caucasians.

In an autopsy study on 29 male and 27 female Aborigines and 57 male and 37 female Caucasians the volumes of a large number of brain regions were determined and fitted to logistic growth functions. For Aboriginal adults significantly smaller values were found for weight and volume of the whole brain, cerebrum, and cerebellum and for the volumes of cerebral white matter, thalamus, amygdaloid body (females only), and globus pallidus (males only). No significant differences were found for caudate nucleus, putamen, amygdaloid body (males only), and globus pallidus (females only). Almost every region studied showed later half-value times, slower growth rates, and prolonged growth phases for Aborigines compared to Caucasians. These results are discussed in relation to secular changes of growth parameters of the human brain during the last century, timing of growth phases for each area, and the socioeconomical and health status of Aborigines.

Adolescent↗
PubMed1989

Atrial natriuretic factor and renin-aldosterone in volume regulation of patients with cirrhosis.

The role of the atrial natriuretic factor and of the main counteracting sodium-retaining principle, the renin-aldosterone system, in acute volume regulation of cirrhosis of the liver has been investigated. Central volume stimulation was achieved in 21 patients with cirrhosis, 11 without and 10 with ascites, and 25 healthy controls by 1-hr head-out water immersion. Immersion prompted a highly significant (p less than 0.001) increase of atrial natriuretic factor plasma concentrations in cirrhotic patients without ascites from 8.5 +/- 1.3 fmoles per ml to 16.5 +/- 2.6 fmoles per ml, comparable to the stimulation in control subjects (6.0 +/- 0.6 fmoles per ml to 13.6 +/- 2.6 fmoles per ml). In cirrhotic patients with ascites, atrial natriuretic factor increase (from 7.7 +/- 1.3 fmoles per ml to 11.4 +/- 2.3 fmoles per ml) was blunted (p less than 0.05). Plasma renin activity and plasma aldosterone concentration were elevated in cirrhotic patients, especially in the presence of ascites. Following immersion, plasma renin activity and plasma aldosterone concentration were reduced similarly in all groups. Water immersion induced a more pronounced natriuresis and diuresis in control subjects than in cirrhotic patients. Neither atrial natriuretic factor nor plasma renin activity nor plasma aldosterone concentration alone correlated to sodium excretion. However, atrial natriuretic factor to plasma aldosterone concentration ratios were closely correlated to basal and stimulated natriuresis in cirrhotic patients, particularly in those with ascites. These data suggest that atrial natriuretic factor and the renin-aldosterone system influence volume regulation in patients with cirrhosis.

Adult↗
PubMed1989

The effect of PAF in the cochlea of guinea pigs.

The influence of 10(-10) and 10(-9) M PAF/animal given into the jugular vein over 30 sec on inner ear potentials, i.e. endolymphatic potential (EP), summating potential (SP) and cochlear microphonics (CM) was investigated. The EP showed the most pronounced changes. When infusing a specific PAF receptor antagonist, ginkgolide B, or the TXA2 receptor antagonist, sulotraban, before the the infusion of PAF, the changes in cochlear potentials could be completely prevented. A second TXA2 receptor antagonist, daltroban, did not effectively prevent PAF actions. It is hypothesized that these PAF effects are due to an interference with ion transport in the non-sensory structures of the inner ear.

Acoustic Stimulation↗
PubMed1988

The effect of substances influencing the arachidonic acid cascade on experimental cardiac arrhythmias.

Substances shifting the balance between thromboxane (TX) and prostacyclin (PGI2) in favour of PGI2 could be of therapeutic value for arrhythmia treatment. This seems to be independent of the pathogenetic mechanism. The TX receptor antagonist BM 13177, the lipoxygenase inhibitor esculetin were effective in ouabain and aconitine induced arrhythmias while the PGI2 formation stimulating substance nafazatrom was only effective in aconitine induced arrhythmia. BM 13177 and esculetin could also counteract the arrhythmogenic effect of PAF. TX synthetase inhibition by HOE 944 was ineffective or partially effective, resp..

15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5↗
PubMed1988

[Pathophysiologic and clinical relevance of atrial natriuretic factor in patients with cirrhosis of the liver].

Defects of the ANF system in cirrhosis have not been demonstrated in terms of absolute deficiency of plasma levels or by evidence of major abnormalities of processing in patients with cirrhosis. In the present study, the responsiveness of the ANF system to acute volume stimulation by water immersion and the diuretic and natriuretic effects of ANF infusion were examined. Stimulation of ANF release by 1-h immersion was significantly blunted in ten cirrhotic patients with ascites (increase of plasma ANF by 46 +/- 18%), whereas 11 cirrhotics without ascites showed a 104 +/- 16% increase, similar to the 117 +/- 29% stimulation in 25 healthy controls. Immersion increased urinary volume by 3.6 +/- 0.6/2.0 +/- 0.8/0.7 +/- 0.4 ml/min and urinary sodium excretion by 146 +/- 38/75 +/- 43/43 +/- 19 mumol/min in controls/cirrhotics without/cirrhotics with ascites. Infusion of ANF for 30 min prompted an increase in diuresis and natriuresis in seven cirrhotic patients, which was less marked in patients with ascites, as compared to patients without ascites. Thus, the stimulus response coupling for ANF may be impaired in patients with cirrhosis and ascites.

Ascites↗