Experimental
brain tumors were produced in 20 cats by stereotaxic
xenotransplantation of a blastomatous glial cell clone into the internal capsule of the left hemisphere. Ten of these animals were treated after 2 weeks with a single injection of 10 mg
dexamethasone in crystalline
suspension. Three weeks after
xenotransplantation vascular permeability was studied by electron microscopy with
horseradish peroxidase as the barrier tracer (four animals), and extravasation of
serum proteins was visualized by immunohistochemistry, using an image processing system (16 animals). In animals used for immunohistochemistry, the water content of peritumoral brain tissue was also determined. In both treated and untreated animals, spherical
tumors with a diameter of about 10 mm were present at the implantation site. Extravasation of
horseradish peroxidase was detected only in the
tumor, but there was accumulation of
serum proteins both in the
tumor and the peritumoral white matter.
Edema, in consequence, originated mainly in the
tumor from where it spread into the surrounding brain tissue.
Corticosteroid therapy reduced the water content of peritumoral brain tissue but did not affect increased barrier permeability of
tumor vessels, and only slightly improved peritumoral accumulation of
serum proteins. It is concluded that amelioration of
tumor edema by
corticosteroids cannot result solely from tightening of the blood-brain barrier to circulating macromolecules but must be due to an active restoration of cerebral water homeostasis despite persisting
serum protein extravasation.