A QUANTITATIVE STUDY OF VASCULAR PERMEABILITY TO HORSERADISH PEROXIDASE, AND THE SUBSEQUENT FATE OF THE TRACER, IN RAT BRAINS AFTER PORTOCAVAL ANASTOMOSIS

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Abstract
Labeled blood vessel segments, exudation patches and pericytic granular cells were counted in sections of rat brain which was fixed and tested with DAB [diamino-benzidine tetrahydrochloride] from 3 min to 24 h after i.v. injection of horseradish peroxidase (HRP). In normal rats, 3 min after injection, only 1% of the total blood vessel segments had walls penetrated by HRP, but in rats 14 days after portocaval anastomosis (PCA) 44% of the total segments had labeled walls, a frequency of 3033 permeable segments/mm3 of brain. In normal rats no exudation patches were found, but after PCA there were 7 patches/mm3 of brain. Maximum vascular wall labeling and maximum exudation occurred in the cerebellum and medulla of the operated rats. Hardly any pericytic cells were labeled 3 min after injection. In operated rats 2 h after injection of HRP, labeled vascular walls were fewer and exudation had disappeared, but 204 pericytic cells/mm3 of brain contained HRP-labeled granules, i.e., 60% of the total pericytes. Highest numbers were found in the most anterior section of the brain sample. Later after injection these numbers declined. Most of the protein which leaked into the brain after PCA returned to the blood whence it came, but some was captured and hydrolyzed by the granular pericytes.