2,067 research outputs found
Disparate responses of tumour vessels to angiotensin II: tumour volume-dependent effects on perfusion and oxygenation
Perfusion and oxygenation of experimental tumours were studied during angiotensin II (AT II) administration whereby the rate of the continuous AT II infusion was chosen to increase the mean arterial blood pressure (MABP) by 50–70 mmHg. In subcutaneous DS- sarcomas the red blood cell (RBC) flux was assessed using the laser Doppler technique and the mean tumour oxygen partial pressure (p O 2) was measured polarographically using O 2-sensitive catheter and needle electrodes. Changes in RBC flux with increasing MABP depended mainly on tumour size. In small tumours, RBC flux decreased with rising MABP whereas in larger tumours RBC flux increased parallel to the MABP. As a result of these volume-dependent effects on tumour blood flow, the impact of AT II on tumour p O 2 was also mainly tumour volume-related. In small tumours oxygenation decreased with increasing MABP during AT II infusion, whereas in large tumours a positive relationship between blood pressure and O 2 status was found. This disparate behaviour might be the result of the co-existence of two functionally distinct populations of tumour vessels. In small tumours, perfusion decreases presumably due to vasoconstriction of pre-existing host vessels feeding the tumour. In larger malignancies, newly formed tumour vessels predominate and seem not to have this vasoresponsive capability (lack of smooth muscle cells and/or AT receptors), resulting in an improvement of perfusion which is not tumour-related per se, but is due to the increased perfusion pressure. © 2000 Cancer Research Campaig
Dynamic interplay between tumour, stroma and immune system can drive or prevent tumour progression
In the tumour microenvironment, cancer cells directly interact with both the
immune system and the stroma. It is firmly established that the immune system,
historically believed to be a major part of the body's defence against tumour
progression, can be reprogrammed by tumour cells to be ineffective,
inactivated, or even acquire tumour promoting phenotypes. Likewise, stromal
cells and extracellular matrix can also have pro-and anti-tumour properties.
However, there is strong evidence that the stroma and immune system also
directly interact, therefore creating a tripartite interaction that exists
between cancer cells, immune cells and tumour stroma. This interaction
contributes to the maintenance of a chronically inflamed tumour
microenvironment with pro-tumorigenic immune phenotypes and facilitated
metastatic dissemination. A comprehensive understanding of cancer in the
context of dynamical interactions of the immune system and the tumour stroma is
therefore required to truly understand the progression toward and past
malignancy.Comment: 36 pages, 4 figures, 1 tabl
Temperature-induced smearing of the coulomb gap: experiment and computer simulation
We present the first verification of the theoretically predicted effect of temperature-induced smearing of the Coulomb gap. Measurements of the variable-range-hopping conductivity (VRH) in samples of ion-implanted Si:As and computer simulation are used to study the density of states (DOS) near the Fermi level (FL) in the impurity band. The VRH is determined by the DOS integrated over some energy range that depends on temperature T and on the magnetic field B. Using the interplay between T and B we find that the DOS in the vicinity of the FL increases with increasing T
Patterns and localized structures in bistable semiconductor resonators
We report experiments on spatial switching dynamics and steady state
structures of passive nonlinear semiconductor resonators of large Fresnel
number. Extended patterns and switching front dynamics are observed and
investigated. Evidence of localization of structures is given.Comment: 5 pages with 9 figure
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