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  • 1
    Electronic Resource
    Electronic Resource
    Nitrate and ammonium influxes in soybean (Glycine max) roots: direct comparison of 13N and 15N tracing (1996)
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 19 (1996), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: We compared influxes and internal transport in soybean plants (Glycine max cv. Kingsoy) of labelled N from external solutions where either ammonium or nitrate was labelled with the stable isotope15N and the radioactive isotope13N. The objective was to see whether mass spectrometric determinations of tissue 15N content were sufficiently sensitive to measure influxes accurately over short time periods. Our findings were as follows. (1) There was a close quantitative correspondence between estimates of N influx of individual plants using 15N or 13N measurements with either NO3/− or NH4+ at 4 or 2 mol−3, respectively in the external solution. (2) Transport to the shoot of N from NO3 absorbed over a 5–15 min period could be monitored when the external NO3− concentration ranged from 0–05 to 4 mol m−3. NH4+ as the N source labelled shoot tissue more slowly, and estimates of the transport between root and shoot could be made only with 13N. (3) Influx of NO3− into root tissue could be measured by 15N enrichment after 5–10 min at concentrations approaching the probable KM of the high-affinity transport system. (4) There was some indication of isotope discrimination, especially with respect to the movement of labelled N to the shoot, when NO3− is the N source.For many purposes, 15N tracing can be used satisfactorily to estimate influxes of both NO3− and NH4+ in soybean roots. Use of the short-lived radio nuclide 13N remains the method of choice for more refined measurements of internal distribution and assimilation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-3040.1996.tb00422.x
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  • 2
    Electronic Resource
    Electronic Resource
    On the principles underlying the diagnosis of brain tumours — A survey article (1995)
    Springer
    Acta neurochirurgica 135 (1995), S. 1-11 
    Details
    ISSN: 0942-0940
    Keywords: Brain tumour ; brain oedema ; blood brain barrier
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary A survey is given of the principles underlying the diagnosis of brain tumours. Traditionally diagnosis and localization of brain tumours have been based upon morphological criteria. Currently unsurpassed levels in imaging of anatomical details and topographical relations by the techniques of computed tomography (CT) and magnetic resonance imaging (MRI) have been achieved. The techniques of positron emission tomography (PET) and of magnetic resonance spectroscopy (MRS), which depict also metabolic and blood flow aspects, provide a refinement of our knowledge on the metabolism, structure and pathophysiological relations of a tumour to the surrounding parenchyma. Recent advances in the recording of function-related changes of the cerebral electro-magnetic field allow a better definition of critical functional areas.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02307407
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Localised proton spectroscopy and spectroscopic imaging in cerebral gliomas, with comparison to positron emission tomography (1995)
    Springer
    Neuroradiology 37 (1995), S. 198-206 
    Details
    ISSN: 1432-1920
    Keywords: Gliomas ; Proton magnetic resonance spectroscopy ; Proton magnetic resonance spectroscopic imaging ; Brain oedema ; Positron emission tomography
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract In 32 patients with gliomas, one- and two-dimensional proton magnetic resonance spectroscopy (1H-MRS) has been conducted, the latter allowing reconstruction of spectroscopic data into a spectroscopic image (MRSI), showing the distribution of the various metabolite concentrations over the cross-sectional plane. For lack of absolute concentrations, the measured concentrations of phosphocholine (CHOL),N-acetyl-L-aspartate (NAA), and lactate (LAC) were conventionally expressed in ratios relative to that of creatine (CREAT). Compared to normal brain tissue, an increased CHOL/CREAT ratio was found in all groups of tumours, in glioblastomas, high-, middle- and low-grade astrocytomas both at the margin and the core of the tumours, but in oligodendrogliomas only at the margin. This is consistent with an increased phosphocholine turnover in relation to membrane biosynthesis by the proliferating cells. The NAA/CREAT ratio was decreased in all groups of tumours, both in the centre and at the margin, reflecting replacement of functioning neurons by neoplastic cells. The LAC/ CREAT ratio was elevated in the core of malignant gliomas, which may be the result of a prevailing glycolysis, characteristic of tumours, possibly in conjunction with hypoxia/ischaemia. In the perifocal oedema, there was neither elevation of the CHOL/CREAT ratio nor decrease of the NAA/CREAT ratio; an increased LAC/CREAT ratio therefore rather reflected ischaemia/hypoxia probably due to locally elevated pressure and compromised regional perfusion. In the normal brain, the metabolite ratios of grey matter did not differ from those of white matter. The frontal lobe and basal ganglia showed lower NAA/CREAT ratios than the other cerebral areas. In 7 patients positron emission tomography was also performed with [18F]fluoro-2-deoxy-D-glucose (18FDG) or L-[1-11C]-tyrosine (11C-TYR); the latter demonstrated a pattern of11C-TYR uptake similar to that of CHOL elevation in the MRSI.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01578258
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  • 4
    Electronic Resource
    Electronic Resource
    Localised proton spectroscopy and spectroscopic imaging in cerebral gliomas, with comparison to positron emission tomography (1995)
    Springer
    Neuroradiology 37 (1995), S. 198-206 
    Details
    ISSN: 1432-1920
    Keywords: Key words Gliomas ; Proton magnetic resonance spectroscopy ; Proton magnetic resonance spectroscopic imaging ; Brain oedema ; Positron emission tomography
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract In 32 patients with gliomas, one- and two-dimensional proton magnetic resonance spectroscopy (1H-MRS) has been conducted, the latter allowing reconstruction of spectroscopic data into a spectroscopic image (MRSI), showing the distribution of the various metabolite concentrations over the cross-sectional plane. For lack of absolute concentrations, the measured concentrations of phosphocholine (CHOL), N -acetyl-L-aspartate (NAA), and lactate (LAC) were conventionally expressed in ratios relative to that of creatine (CREAT). Compared to normal brain tissue, an increased CHOL/CREAT ratio was found in all groups of tumours, in glioblastomas, high-, middle- and low-grade astrocytomas both at the margin and the core of the tumours, but in oligodendrogliomas only at the margin. This is consistent with an increased phosphocholine turnover in relation to membrane biosynthesis by the proliferating cells. The NAA/CREAT ratio was decreased in all groups of tumours, both in the centre and at the margin, reflecting replacement of functioning neurons by neoplastic cells. The LAC/CREAT ratio was elevated in the core of malignant gliomas, which may be the result of a prevailing glycolysis, characteristic of tumours, possibly in conjunction with hypoxia/ischaemia. In the perifocal oedema, there was neither elevation of the CHOL/CREAT ratio nor decrease of the NAA/CREAT ratio; an increased LAC/CREAT ratio therefore rather reflected ischaemia/hypoxia probably due to locally elevated pressure and compromised regional perfusion. In the normal brain, the metabolite ratios of grey matter did not differ from those of white matter. The frontal lobe and basal ganglia showed lower NAA/CREAT ratios than the other cerebral areas. In 7 patients positron emission tomography was also performed with [18F]fluoro-2-deoxy-D-glucose (18FDG) or L-[1-11C]-tyrosine (11C-TYR); the latter demonstrated a pattern of 11C-TYR uptake similar to that of CHOL elevation in the MRSI.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01578258
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    Paper (German National Licenses)
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  • 5
    Electronic Resource
    Electronic Resource
    Visualization of multidrug resistance in vivo (1999)
    Springer
    European journal of nuclear medicine 26 (1999), S. 283-293 
    Details
    ISSN: 1619-7089
    Keywords: Key words: Multidrug resistance ; Single-photon emission tomography ; Positron emission tomography ; P-glycoprotein ; Multidrug resistance-associated protein
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract. Various mechanisms are involved in multidrug resistance (MDR) for chemotherapeutic drugs, such as the drug efflux pumps, P-glycoprotein (Pgp) and multidrug resistance-associated protein (MRP). In this review the mechanisms involved in MDR are described and results are reviewed with particular attention to the in vivo imaging of Pgp and MRP. Various detection assays provide information about the presence of drug efflux pumps at the mRNA and protein levels. However, these methods do not yield information about the dynamic function of Pgp and MRP in vivo. For the study of Pgp- and MRP-mediated transport, single-photon emission tomography (SPET) and positron emission tomography (PET) are available. Technetium-99m sestamibi is a substrate for Pgp and MRP, and has been used in clinical studies for tumour imaging, and to visualize blockade of Pgp-mediated transport after modulation of the Pgp pump. Other 99mTc radiopharmaceuticals, such as 99mTc-tetrofosmin and several 99Tc-Q complexes, are also substrates for Pgp, but to date only results from in vitro and animal studies are available for these compounds. Several agents, including [11C]colchicine, [11C]verapamil and [11C]daunorubicin, have been evaluated for the quantification of Pgp-mediated transport with PET in vivo. The results suggest that radiolabelled colchicine, verapamil and daunorubicin are feasible substrates with which to image Pgp function in tumours. Uptake of [11C]colchicine and [11C]verapamil is relatively high in the chest area, reducing the value of both tracers for monitoring Pgp-mediated drug transport in tumours located in this region. In addition, it has to be borne in mind that only comparison of Pgp-mediated transport of radioalabelled substrates in the absence and in the presence of Pgp blockade gives quantitative information on Pgp-mediated pharmacokinetics. Leukotrienes are specific substrates for MRP. Therefore, N-[11C]acetyl-leukotriene E4 provides an opportunity to study MRP function non-invasively. Results obtained in MRP2 mutated GY/TR rats have demonstrated visualization of MRP-mediated transport. This tracer permits the study of MRP transport function abnormalities in vivo, e.g. in Dubin-Johnson patients, who are MRP2 gene deficient. Results obtained show the feasibility of using SPET and PET to study the functionality of MDR transporters in vivo.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002590050390
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