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排序方式: 共有58条查询结果,搜索用时 187 毫秒
1.
Nguyen T. Buu 《Journal of neurochemistry》1985,45(2):470-476
An increase of free 3,4-dihydroxyphenylethylamine (DA, dopamine) in the rat brain such as is found following 3,4-dihydroxyphenylalanine (L-DOPA) administration or an intraventricular injection of free dopamine did not result in DA sulfate formation, despite the presence of phenolsulfotransferase activity in various regions of the brain and the high affinity of DA for this enzyme. However, when rats were pretreated with pargyline, a monoamine oxidase inhibitor, the same treatment with L-DOPA or free DA led to active synthesis of DA sulfate. The increase in DA sulfate was significantly correlated with the degree of monoamine oxidase inhibition and directly proportional to free DA concentrations in the hypothalamus (r = 0.86), striatum (r = 0.54), and brainstem (r = 0.89). The highest ratio of DA sulfate to free DA was found in the hypothalamus, suggesting that sulfoconjugation is most active in this region. Prior treatment of rats with 6-hydroxydopamine did not decrease DA sulfate concentrations, indicating that sulfoconjugation occurs most likely in extraneuronal tissues not destroyed by the neurotoxin. The results are compatible with the notion that phenolsulfotransferase may be highly compartmentalized and that inhibition of monoamine oxidase allows the newly generated free DA to become accessible to the sulfoconjugating enzyme, resulting in increase in DA sulfation. 相似文献
2.
Cycling of soil carbon in the first year after a clear-felling was compared with that before the felling in a Japanese red
pine forest in Hiroshima Prefecture, west Japan. The daily mean temperature at the soil surface in summer was increased after
the felling in comparison to that before felling, and the water content of both the A0 layer and the surface mineral soil was decreased due to the loss of the forest canopy. The rate of weight loss of the A0 layer was reduced after felling. However, accumulation of the A0 layer rapidly decreased because of the lack of litter supply to the forest floor. Low soil respiration after felling was
mainly caused by the cessation of root respiration. Analysis of annual soil carbon cycling was then conducted using a compartment
model. The relative decomposition rate of the A0 layer decreased whereas that of humus and dead roots in mineral soil increased to some extent after felling. The accumulation
of carbon in mineral soil, however, increased slightly due to the supply of humus from roots killed by the felling. 相似文献
3.
Norman T. J. Bailey 《Journal of mathematical biology》1982,14(1):101-116
It is shown how a multicompartmental infectious disease model can be systematically examined for reduction of structural complexity. For steadystate situations, four basic rules are proposed for eliminating components of flow-lines, whole flow-lines, and compartments, plus combining compartments. An application to a typhoid fever model allows calculations to be done on a pocket calculator. The approach could be particularly important in developing countries. 相似文献
4.
Katrin Paul Katharina Bttinger Bernd M. Mitic Georg Scherfler Christoph Posch Dirk Behrens Christian G. Huber Christoph Herwig 《Engineering in Life Science》2020,20(8):368-378
Large‐scale bioreactors for the production of monoclonal antibodies reach volumes of up to 25 000 L. With increasing bioreactor size, mixing is however affected negatively, resulting in the formation of gradients throughout the reactor. These gradients can adversely affect process performance at large scale. Since mammalian cells are sensitive to changes in pH, this study investigated the effects of pH gradients on process performance. A 2‐Compartment System was established for this purpose to expose only a fraction of the cell population to pH excursions and thereby mimicking a large‐scale bioreactor. Cells were exposed to repeated pH amplitudes of 0.4 units (pH 7.3), which resulted in decreased viable cell counts, as well as the inhibition of the lactate metabolic shift. These effects were furthermore accompanied by increased absolute lactate levels. Continuous assessment of molecular attributes of the expressed target protein revealed that subunit assembly or N‐glycosylation patterns were only slightly influenced by the pH excursions. The exposure of more cells to the same pH amplitudes further impaired process performance, indicating this is an important factor, which influences the impact of pH inhomogeneity. This knowledge can aid in the design of pH control strategies to minimize the effects of pH inhomogeneity in large‐scale bioreactors. 相似文献
5.
Measurement of exchange of substances between blood and tissue has been a long-lasting challenge to physiologists, and considerable theoretical and experimental accomplishments were achieved before the development of the positron emission tomography (PET). Today, when modeling data from modern PET scanners, little use is made of earlier microvascular research in the compartmental models, which have become the standard model by which the vast majority of dynamic PET data are analysed. However, modern PET scanners provide data with a sufficient temporal resolution and good counting statistics to allow estimation of parameters in models with more physiological realism. We explore the standard compartmental model and find that incorporation of blood flow leads to paradoxes, such as kinetic rate constants being time-dependent, and tracers being cleared from a capillary faster than they can be supplied by blood flow. The inability of the standard model to incorporate blood flow consequently raises a need for models that include more physiology, and we develop microvascular models which remove the inconsistencies. The microvascular models can be regarded as a revision of the input function. Whereas the standard model uses the organ inlet concentration as the concentration throughout the vascular compartment, we consider models that make use of spatial averaging of the concentrations in the capillary volume, which is what the PET scanner actually registers. The microvascular models are developed for both single- and multi-capillary systems and include effects of non-exchanging vessels. They are suitable for analysing dynamic PET data from any capillary bed using either intravascular or diffusible tracers, in terms of physiological parameters which include regional blood flow. 相似文献
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Cytotoxic drugs administered in polychemotherapy cause a characteristic neutropenic period depending on the schedule of the drugs, which can partly be prevented by G-CSF growth factor support. To quantify these effects and to gain a deeper insight into the dynamics of bone marrow recovery after such suppressing and stimulating disturbances, we construct a biomathematical compartment model of human granulopoiesis under polychemotherapy with G-CSF support. The underlying assumptions and mathematical techniques used to obtain the model are explained in detail. A large variety of biological and clinical data as well as knowledge from a model of murine haematopoiesis are evaluated to construct a physiological model for humans.Particular emphasis is placed on estimating the influence of chemotherapeutic drugs on the granulopoietic system. As a result, we present an innovative method to estimate the bone marrow damage caused by cytotoxic drugs with respect to single identifiable cell stages only on the basis of measured peripheral blood leukocyte dynamics. Conversely, our model can be used in a planning phase of a clinical trial to estimate the haematotoxicity of regimens based on new combinations of drugs already considered and with or without growth factor support.Acknowledgement This paper was supported by the DFG (Deutsche Forschungsgemeinschaft) in the framework of the project Aufbau von Simulationsmodellen der h{\a}matopoetischen Dynamik nach konventioneller und hochdosierter Chemotherapie und Zytokingabe beim Menschen (Nr. LO 342/8-2). We would like to thank the German High Grade Non-Hodgkins-Lymphoma Study Group and the German Hodgkins Lymphoma Study Group for the kind provision of data. 相似文献
9.
Fan Y Soller M Flister S Hollmann M Müller M Bello B Egger B White K Schäfer MA Reichert H 《Developmental biology》2005,287(1):61-73
The correct targeting of photoreceptor neurons (R-cells) in the developing Drosophila visual system requires multiple guidance systems in the eye-brain complex as well as the precise organization of the target area. Here, we report that the egghead (egh) gene, encoding a glycosyltransferase, is required for a compartment boundary between lamina glia and lobula cortex, which is necessary for appropriate R1-R6 innervation of the lamina. In the absence of egh, R1-R6 axons form a disorganized lamina plexus and some R1-R6 axons project abnormally to the medulla instead of the lamina. Mosaic analysis demonstrates that this is not due to a loss of egh function in the eye or in the neurons and glia of the lamina. Rather, as indicated by clonal analysis and cell-specific genetic rescue experiments, egh is required in cells of the lobula complex primordium which transiently abuts the lamina and medulla in the developing larval brain. In the absence of egh, perturbation of sheath-like glial processes occurs at the boundary region delimiting lamina glia and lobula cortex, and inappropriate invasion of lobula cortex cells across this boundary region disrupts the pattern of lamina glia resulting in inappropriate R1-R6 innervation. This finding underscores the importance of the lamina/lobula compartment boundary in R1-R6 axon targeting. 相似文献
10.
As we are entering the post-genomic era, models-of-data, such as mining and filtering methods for gene sequences and microarrays and the clustering of co-expressed genes, must be complemented with models-of-processes that explain relationships between genomic information and phenomena at biochemical and physiological levels. Many of these models will have the structure of compartment models, whose conceptualization, identification and analysis will fundamentally benefit from the seminal work of John Jacquez. The article indicates with three vignettes that non-linear compartment models in the formulation of biochemical systems theory are viable candidates for post-genomic models-of-processes. 相似文献