Cerebral pathophysiology in hemorrhagic shock. Nuclide scan data, fluorescence microscopy, and anatomic correlations.

Nineteen unanesthetized sheep were given Evans blue dye or radionuclide and then were incrementally bled into hemorrhagic shock (BP less than 50/25) by withdrawal of blood over a period of approximately one hour. Four sheep served as controls for histologic data. Static nuclide brain scans performed in 6 bled sheep demonstrated immediate uptake of the radionuclide. Fluroescence microscopic examination of brain tissue obtained at autopsy in bled sheep demonstrated dye uptake in the perivascular areas, but not in the neuropil. Electron microscopic examination of collateral cortical biopsy specimens showed swelling of perivascular astrocytic foot processes, but no endothelial abnormality. We feel that the uptake of radionuclide and dye-albumin complex by the perivascular astrocytes represents enhanced transendothelial transport rather than passage of molecules between endothelial cells. The significance of this presumably transient phenomenon is discussed.