The unique features of brain capillary and microvascular endothelial cells embrace specialized transport and carrier systems as well as enzymes associated with various metabolic pathways that are essential to sustain the dynamic homeostasis of the brain [2, 39]. Many of these processes are thought to be neuronally regulated [47]. It is now widely accepted that cerebral vascular endothelial cells not only constitute a permeability barrier to ions and organic molecules (e.g., water, electrolytes, proteins, neurotransmitters), but they are also an important secretory organ. BCEC produce agents and factors that may be involved in autocrine and paracrine regulation of the microvascular function of the brain [30, 41, 44, 50]. In general, the substances (e.g., prostacyclin, nitric oxide (NO), and adenosine) produced by these cells are considered to be cytoprotective. However, several other agents which are formed in endothelial cells (i.e., endothelin-1 (ET-1), angiotensin II, thromboxane, leukotrienes, platelet-activating factor and superoxide radicals) impair perfusion, alter BBB permeability and/or mediate cellular injury when released in excess. Many of these substances which modulate the secretory functions and reactivities of the vascular endothelium can also be released from adjacent cellular elements including other vascular cells, circulating blood cells and brain cells