The permeability of the blood-brain barrier and cell membranes to horseradish peroxidase in hyperammonaemia

Summary

The permeability of the blood-brain barrier and of the cell membranes to intravenously (i.v.) injected horseradish peroxidase was investigated in rats after 4 days with urease-induced hyperammonaemia. Increased permeability across the vessels was not observed. The endothelial tight junctions were intact, and the clefts between adjacent endothelial cells were devoid of reaction product. A few vesicles containing horseradish peroxidase could be seen in the cytoplasm of the endothelium. Diffuse dispersion of tracer in the cytoplasm was not found. Reaction product was demonstrated in the subendothelial basement membranes of a few arteriolar segments, as under normal conditions.

With the purpose of examining the cell membranes, peroxidase was infused in other rats into the cerebral ventricles via a stab wound followed by examination of the contralateral hemisphere. With the exception of a few vesicles and caveolae, intracellular distribution of the reaction product was not observed. Horseradish peroxidase was located in the entire extracellular space beneath the ependyma and pia and in the basement membranes of several vessels. Reaction product was also observed in endothelial vescles, close to or in contact with the basement membrane. In addition, peroxidase could occur on the luminal surface of the endothelial cells. It is concluded that the permeability properties to horseradish peroxidase of the blood-brain barrier, as well as of the cell membranes, are unchanged in rats exposed to urease-induced hyperammonaemia for 4 days.