Two methods for three-dimensional examination of the pattern of vasculature in tumours

Selective closure of the vascular bed of an experimental glioma model during in situ saline perfusion

Flow through the vasculature of an experimental rat glioma has been investigated during in situ perfusion of the brain, via the ascending aorta, with a simple saline solution. Using such a system, it has been shown previously that the blood-brain barrier will remain intact with an adequate cerebral perfusate flow rate for at least 10 min, providing that the metabolic inhibitor 2,4-dinitrophenol is present. Cerebral perfusate flow rate was measured in both tumour and non-tumour areas using [14C] iodoantipyrine. The perfusion pump rate was set between 4.8 and 84 ml/min in different animals and the mean flow rate for cerebral hemisphere remote from the tumour was 1.03 +/- 0.67 ml/min/g (mean +/- sd; n = 17) whereas that for intracerebral tumour was considerably lower at 0.060 +/- 0.11 ml/min/g (mean +/- sd; n = 17). Linear regression of tumour flow on cerebrum flow showed a highly significant correlation (r = 0.88). Light and electron microscope examination of the tumour vessels revealed no luminal obstruction or perivascular oedema to explain the low flow. We suggest that perfusion with a low viscosity medium, at flow rates that result in a low intraluminal pressure, probably causes glioma vessels to close preferentially because they require a higher intraluminal pressure to remain patent than do normal cerebral vessels.

The vascular response to tumor infiltration in malignant gliomas. Morphometric and reconstruction study

Neo-vascularization and endothelial hyperplasia have been shown to be very active in malignant gliomas. In this contribution the vascularization of the cortex infiltrated by malignant gliomas is morphometrically studied and the endothelial proliferations are immunohistochemically investigated and reconstructed by a three-dimensional computer-assisted procedure. Vessel density increases after tumor infiltration in some cases only. The diameter of vessels increases and so does the number of nuclei/vessel after the complete invasion of the cortex when vascular glomeruli develop. In completely infiltrated cortex with development of glomeruli and circumscribed necroses, vessel density is very low. No neoformation of vessels takes place before the complete infiltration of the cortex by the tumor. The hyperplastic formations, usually arranged parallel to the deep or outer cortical layers, take origin from the radially penetrating vessels from the meninges and their lateral branching. The hyperplasia deforms the vascular network, making it often inadequate to supply tumor cells. Immunohistochemically, the cells composing the hyperplastic structures are variably positive for factor VIII/RAg and, at a lesser extent, for alpha-smooth muscle actin. The poorness of the vascular network in many instances of completely infiltrated cortex is responsible for the development of circumscribed necroses.

Tumor-related angiogenesis

In recent years, tumor-related angiogenesis has become an important field of research in oncology. It could be stated that growth of solid tumors is completely dependent on neovascularization to provide the tumor with all required nutrients. Special compounds (tumor angiogenesis factor[s]) are released by tumor cells into the environment to stimulate different types of normal cells to become active for the tumor. In particular, endothelial cells of neighboring capillaries are induced to react. They disintegrate their own basal lamina, detach from their neighbors, enter the extracellular matrix, and migrate toward the tumor mass. Cell divisions occur within such sprouts, thereby increasing the number of migrating endothelial cells. Strands of such cells are formed, and inter- and intracellular lumina develop. Loops of these hollow strands anastomose to form a network of new vessels which become connected with the blood circulation. The tumor mass thus becomes vascularized and can continue to grow. The prevention of neoangiogenesis has an enormous impact on cancer treatment by inhibiting the growth of the tumor. In this review, all important aspects of tumor-related angiogenesis are presented.

A morphometric study of the microvasculature of a rat glioma

Intracerebral tumours were produced in BD IX rats by the inoculation of neoplastic astrocytes. Following perfusion-fixation, 1.0 micron sections were stained with toluidine-blue and photographed so as to construct photomontages embracing deep tumour, tumour edge and surrounding brain. Thirteen montages from 9 tumours were studied. Successive 200 micron samples were analysed with a digitizing tablet and, for each sample the following were measured: the number of vascular profiles per unit area, the mean vessel circumference and diameter and the approximate fractions of the sample occupied by tumour and necrosis. Towards the tumour centre, vascular density dropped to 20% of that for normal cortex but vessel size more than doubled. The surface area fraction of the vessels reached a maximum at the tumour edge. These results provide not only an anatomical framework for both a variety of physiological studies and for the investigation of angiogenesis in this system but also have pharmacokinetic implications for the treatment of brain tumours.

The effect of radiation alone and of radiation followed by hyperthermia on the vasculature of mouse intestine

The effect on the vasculature of mouse intestine was observed following: (a) irradiation alone; and (b) irradiation followed at intervals of 0-60 days by hyperthermia. Specimens of intestine were removed after sacrifice and the vasculature revealed by benzidine staining before clearing in resin. The mean visible venous tree (VVT) was used as a parameter for assessing damage. The same hyperthermal treatment was used throughout: 1 h at 41.0 degrees C with the gut externalised. Following irradiation by 9 Gy, the VVT was not significantly reduced in the first 15 days, but decreased steadily by 34% in the next 45 days. In addition two transient reversible reductions occurred: the first immediately following irradiation, not counteracted by hyperthermia and thought to result from spasm; the second after about 40 days, counteracted by heating and thought to be caused by partial occlusion of the arterioles, resulting from irradiation. Reduction in VVT 26 days after irradiation appeared to be independent of dose from 6 to 10 Gy. Sensitivity to hyperthermia was maximal 15 days after irradiation.

The effect of elevated temperature on the vasculature of mouse jejunum

The effect of elevated temperature on mouse jejunal vasculature was investigated. Both local and lower-body heating were employed, using a hot water bath; heating time was kept constant at 1 hour, bath temperatures ranging from 40.0 degrees C to 43.0 degrees C. Animals were sacrificed after heating, the erythrocytes were stained with benzidine and H2O2 and the blood vessels revealed by mounting in a clearing resin. The earliest damage seen was the disappearance of capillaries, followed by loss of progressively larger vessels. Loss is interpreted as destruction, not merely as interruption of blood flow. A gradient of sensitivity occurs from the inner layer of the jejunum to the outer, the threshold heating temperature required to produce vascular damage being lowest at the inside. Neither temperature gradient, nor early release of gastric juice from the stomach, appears responsible for this differential response. The mean length of intact venous tree was employed as a parameter for assessing the damage.

Differences in vascular pattern between the spontaneous and the transplanted C3H mouse mammary carcinoma

The transplanted C3H tumor differs from the spontaneous in its multi-focal origin and in its increasing loss of differentiation. Loss of differentiation is principally important in that even the partial branching into lobes, which occurs in the spontaneous tumour, is lost and that the parenchyma no longer consists of single-layered and multi-layered tubules, as in the spontaneous tumour, but of multi-layered only. Absence of branching removes the interlobular pressures, which in spontaneous tumours lead to infarction of the efferent vessels and sinus formation. Consequently; sinuses are absent from the transplanted tumour and the circulation is thereby improved. In contrast, since the vascular pattern of the spontaneous tumour is preserved and capillaries do not penetrate into the multi-layered tubules, although these have developed into solid cylinders, the diffusion pathway of oxygen is extended, resulting in necrosis at their cores. Accumulating necrotic fluid is at first removed by lymphatics, but subsequently invades the efferent vascular system. These changes are reflected in the pattern of tumour growth and in the radiation responses.