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The passage of substances across the blood-brain barrier (BBB) is regulated in the cerebral capillaries, which possess certain distinct different morphological and enzymatic properties compared with the capillaries of other organs. Investigations of the functional characteristics of brain capillaries have been facilitated by the use of cultured brain endothelial cells, but in most studies some characteristics of the in vivo system are lost. To provide an in vitro system for studying brain capillary functions, we have developed a process of coculture that closely mimics the in vitro situation by culturing brain capillary endothelial cells on one side of a filter and astrocytes on the other. Under these conditions, endothelial cells retain all the endothelial cell markers and the characteristics of the blood-brain barrier including tight junctions and gamma-glutamyl transpeptidase activity. The average electrical resistance for the monolayer was 661 Ω·cm2. In order to assess the drug transport across the blood-brain barrier, we compared the maximal brain extractions E(0) in vivo to the permeability of the in vitro model. Eleven compounds were tested. They were selected due to their ability to exhibit quantitatively different brain extraction rates. The in vivo and the in vitro values showed a strong correlation as indicated by the Spearman's correlation coefficient (r = 0.83, p |
