Effects of dexamethasone on the blood-brain distribution of albumin and alpha-aminoisobutyric acid in vasogenic cerebral edema.

The effects of dexamethasone (Dex) on the blood-brain distribution of 14C-alpha-aminoisobutyric acid (AIB) and 125I-albumin (RISA) was studied in the rat freeze-lesion model of cerebral edema. Untreated and Dex-treated rats were studied by intravenously administering either AIB or RISA immediately after or one day after localized cortical freezing. The AIB experiments were terminated after 10 min; the RISA experiments were terminated after 30 min or 4 hr. Local tissue distribution of AIB and RISA was assessed by quantitative autoradiography. The distribution of both RISA and AIB within the lesion was unaffected by Dex. In the tissue around the lesion, Dex did not alter the distribution of AIB in the 10 min experiments or of RISA in the 30 min experiments. Dex did, however, diminish the movement of RISA into the adjacent tissue during the 4-hr experiments. The intralesional AIB and RISA distribution data plus the perilesional 10-min AIB and 30-min RISA distribution data indicate that Dex does not act by reducing the flow of solutes and water across damaged or leaky vessels in and around the lesion. The 4-hr RISA data suggests that Dex alters the structure of the extracellular space in the tissue around the lesion (especially in the white matter) and thereby increases the resistance of the interstitium to the flow of solutes and fluid from the lesion into the adjacent tissue.