Effecting change: diversity affects personal and organizational development.
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B R Deane
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The vasculature of experimental brain tumours. Part 3. Permeability studies.
The aim of this work was to elucidate the direction and time-course of transport processes which may affect the accumulation of oedema associated with experimental brain tumours. Astrocytomas were produced in BD-IX rats by intracerebral injection of cultured neoplastic glial cells. The cell line used was cloned from a culture of a primary mixed glioma induced by transplacental administration of N-ethyl-N-nitrosourea (ENU). At various times after cell injection the protein tracer horseradish peroxidase (HRP) was given to tumour-bearing rats, either intravenously or into the lateral ventricles of the brain. The movement of the HRP into tumours and surrounding brain either from blood or from ventricular cerebrospinal fluid (CSF) was studied by light and electron microscopy at various intervals after the injection of the tracer. The time-course of subsequent clearance of the HRP from the tumours and surrounding brain was also investigated. After intravenous injection, HRP rapidly penetrated all vascularized tumours and became evenly distributed within 10-20 min. The HRP remained present in sufficient quantity within the tumours to maintain this intensity for several hours, after which it gradually disappeared, showing no reaction product after 12 h. After intraventricular injection, HRP penetrated periventricular brain tissue up to a maximal distance 1-2 mm within 2 min, and the reaction product remained visible in this region for at least 20 min. In all tumour-bearing animals, HRP penetrated further into periventricular tumour tissue than into adjacent brain tissue. In large tumours HRP reaction product was seen up to 7 mm from the ventricular ependymal lining, although permeation to this distance took up to 10 min.
Animals↗
The vasculature of experimental brain tumours. Part 4. The quantification of vascular permeability.
In order to quantify changes in vessel permeability seen previously in experimental astrocytomas produced in rats by an intracerebral injection of cultured neoplastic glial cells, the flux of mannitol across the vascular endothelium from the blood into the normal brain or tumour tissue was measured using a specially devised technique by which a steady level of radioactively labelled mannitol can be achieved rapidly and maintained in the bloodstream. This is done by a continuous injection given at a rate which is adjusted by a predetermined programme so as to replace the tracer at the rate at which it has been found to leave the circulation in previous experiments. In separate experiments on both tumour-bearing and control rats steady levels of the tracer were maintained in the circulation for progressively longer times of up to 30 min. The kinetic parameters of the process gave estimates for the apparent transfer constant of mannitol across the vascular endothelium and of the size of the extravascular extracellular mannitol space in the tumours. The apparent transfer constant for the movement of mannitol across the blood-brain barrier was increased more than a hundred-fold in the region of the tumour compared to the values for the brain of control rats or that of tumour-bearing rats remote from the tumour site. The extracellular extravascular space within the tumour was estimated to be 22%, somewhat larger than accepted normal values.
Animals↗
The vasculature of experimental brain tumours. Part 1. A sequential light and electron microscope study of angiogenesis.
The process of vascularisation was studied in transplanted astrocytomas in BD-IX rats. The development of blood vessels was followed from the earliest signs of angiogenesis throughout tumour growth. On the basis of tumour vasculature, 3 consecutive stages of tumour growth could be distinguished; avascular, early vascular and late vascular. The tumours grew to a diameter of about 1 mm during the avascular stage after which new capillary sprouts began to penetrate the tumours. This resulted in an homogeneous vasculature of small immature capillaries up to about 5 micrometers in diameter characteristic of the early vascular growth stage. During this stage the tumours reached a diameter of about 4 mm and their vasculature consisted of capillaries similar to those seen in embryological cerebral vascularisation. During the subsequent late vascular stage of growth, continued endothelial proliferation led to an increase in blood vessel diameter up to 50 micrometers in some cases. The vessels varied in shape and size; this vascular pleomorphism and the abnormal morphological features associated with glioma vasculature were typical of the late vascular stage.
Animals↗
The vasculature of experimental brain tumours. Part 2. A quantitative assessment of morphological abnormalities.
Two groups of the morphological abnormalities of brain tumour vasculature described in the previous paper (Deane and Lantos 1981) were quantified. First, blood vessel density, endothelial hyperplasia and endothelial cytology, 3 general features of the vasculature, were assessed, giving a score according to the Microscopic Angiogenesis Grading System (Brem et al. 1972). This not only gives information about the vascular supply of tumours but also often provides a reliable index of malignancy. The system was also adapted for electron microscopy. Secondly, 3 specific features of the endothelial lining were estimated: cytoplasmic vesicle content, fenestrations and abnormal endothelial intercellular junctions, which are thought to represent possible mechanisms of increased trans-endothelial transport. It was found that cytoplasmic vesicle content was 3--6-fold greater in tumour blood vessels than in capillaries from normal brain, and may therefore play an important role in cerebral oedema. However, fenestrations and abnormal endothelial junctions were infrequently seen, and were unevenly distributed.
Animals↗