Increased vesicular transfer of horseradish peroxidase across cerebral endothelium, evoked by acute hypertension.

Acute hypertension in rats was produced by intravenous infusion of metaraminol bitartrate (Aramine). The permeability to intravenously injected horseradish peroxidase (HRP) was increased across the cerebral arterioles, capillaries and venules. From the basement membranes of the vessel walls the protein tracer moved into the extracellular spaces of the adjacent neuropil. No endothelial cell damage was observed. The tight junctions between endothelial cells were intact and prevented intercellular movement of peroxidase. Many HRP-labeled vesicles within the endothelial cells or connected with the luminal or abluminal surface, occurred in segments of the microvasculature. Otherwise the endothelium was unchanged. Diffuse uptake of HRP into the cytoplasm of neurons and glial cells was not observed. The alphablocker phentolamine (Regitin) was given to a group of rats simultaneously to Aramine. The increase in blood pressure was thus prevented; furthermore, the permeability remained as under normal conditions. The Aramine, Regitin and HRP did not significantly influence the pH, PO2 and pCO2 of the arterial blood. It is concluded that acute hypertension increases the vesicular transport of HRP across the endothelium of cerebral arterioles, venules and capillaries that normally occurs to a small extent only after intravenous injection of the tracer.