The Permeability of the Blood-Brain Barrier in Acute Hypertension. Comparison of an Endogenous and Exogenous Protein Tracer

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Abstract
Experimental acute hypertension in male Wistar rats was produced by metaraminol infusion to systemic blood pressure levels of 190–210 mm Hg. After 20 sec or 30 min the animals were killed by perfusion fixation with 8% formaldehyde perfusion. The barrier passage of exogenous HRP (75 mg i.v.) given 10 min before killing (5 rats) and the passage of endogenous anti-HRP antibodies of the IgG class (8 rats, produced by antigenic stimulation beforehand) were compared electron microscopically by semiquantitation of tracer location in unstained ultrathin sections. Five rats served as controls. The number of tracer-filled vesicles was consistently lower in anti-HRP rats than in HRP rats: not only during acute hypertension but also in the controls. The penetration of both tracers into the basement membrane and brain parenchyma, however, was comparable. Anti-HRP was more prominent in the endothelial cytoplasm. Vesicular transport and penetration through the plasma membrane with diffuse cytoplasmic passage tend to be the most likely transport mechanisms, the former for HRP and the latter for the antibody.