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.