Effect of dexamethasone on glial fibrillary acidic protein in peritumorous edema of cats: a morphometric study.

In 54 cats experimental brain tumors were produced by xenotransplantation of the blastomatous glial cell clone RG2 into the internal capsule of the left hemisphere. Fifteen of these animals were treated with dexamethasone for 1 week and four animals for 2 h. The occurrence of glial fibrillary acidic (GFA) protein in tumor and peritumoral edema was studied by immunocytochemistry at intervals ranging between 3 and 35 days after implantation. High concentrations of GFA protein were present in giant and many of the larger tumor cells but not in small tumor cells. In peritumorous white matter it appeared in reactive astrocytes, where it reached its maximum 2 weeks after implantation. At this time, morphometric evaluation of GFA protein-positive areas revealed an increase from 0.095 +/- 0.035% to 5.17 +/- 1.42%. Application of dexamethasone for 1 week reduced this area to 1.67 +/- 0.57% (P less than 0.001). The results obtained demonstrate that the development of peritumorous edema is associated with considerable stimulation of GFA protein production which is inhibited by dexamethasone. Production of GFA protein by reactive astrocytes, in consequence, does not seem to be involved in the resolution process of peritumoral edema under dexamethasone therapy.