The importance of cerebral arterioles in alterations of the blood-brain barrier.

Light and electron microscopy and quantitative estimates of pinocytotic activity in cerebral arterioles and capillaries were performed in two different rat models of altered blood-brain barrier permeability in order to determine the side of initially increased vesicular transport. Seizures were produced by 20 consecutive electroshocks, and ischemic neuronal damage was produced by a 30-minute period of combined right common carotid artery occlusion and systemic hypoxia. Horseradish peroxidase was used to evaluate blood-brain barrier permeability. Serial 1micronm.sections showed an ateriole within most foci of horseradish peroxidase extravasation. There were areas of brain in both experimental groups in which the only permeable vessels were arterioles, and in one ischemic animal, the only permeable vessels were arterioles. Pinocytotic activity was determined in capillaries and arterioles and expressed as the number of horseradish peroxidase-containing pinocytotic vesicles per square millimeter of endothelial cytoplasmic area +/- standard error. The pinocytotic activity in capillaries and arterioles, respectively, was 12.2 +/- 5.4 and 6.7 +/- 3.0 in normal rats, 86.7 +/- 22.1 and 267 +/- 46.1 after seizures, and 52.7 +/- 10.6 and 91.2 +/- 33.2 following cerebral ischemia. These results indicate the importance of the arterioles in maintaining and altering the blood-brain barrier and suggest that abnormal blood-brain barrier permeability occurs first within the arteriole.