Intracerebral arteriolar permeability to lanthanum

Lanthanum, an electron-dense tracer, has been used extensively in the study of the structure of cell junctions. The present study was undertaken to determine whether the interendothelial junctions of normal intracerebral arterioles allow passage of lanthanum and to document the alterations occurring in these structures in acute hypertension. Perfusion of lanthanum for 12-40 minutes in control animals resulted in passage of tracer into arteriolar walls and into the extracellular compartment of the surrounding brain. The two principal mechanisms associated with tracer extravasation into the brain were diffuse passage through endothelial cytoplasm and through interendothelial spaces bypassing tight junctions. The latter finding has not been previously reported in normal cerebral arterioles and suggests that the tight junctions of these vessels are different from those of capillaries and consist of a meshwork of closely arranged maculae occludentes rather than complete circumferential occluding bands as was previously believed. Hypertensive animals showed accelerated passage of lanthanum, it being demonstrable not only in arteriolar walls but in capillary and venular walls and the surrounding neuropil after only 5 minutes of circulation. Passage of tracer through vessel walls occurred by the same routes as in control. In addition, increased numbers of pinocytotic vesicles were observed in the endothelium, confirming our previous studies that increased vesicular transport occurs in cerebral arteriolar endothelium in acute hypertension.