Disturbances of the blood-brain barrier in cerebrovascular disorders.

The disturbances of the BBB in cerebrovascular disorders may affect adversely an underlying basic pathological condition. Breakdown of the barrier associated with extravasation of serum proteins leads to development of vasogenic edema in the brain tissue. An abnormal passage of pharmacologically active substances, such as biogenic amines, may significantly affect cerebral blood flow and metabolism and activate neurons equipped with receptors for these substances. Also, a barrier dysfunction related to faulty out-transport of metabolites may contribute to edema and tissue damage. In cerebral ischemia, following release of arterial occlusion there can be two separate openings of the barrier: the first - occurring promptly after recirculation and related to ensuing reactive hyperemia, the second - after some delay and related to pathological changes in the brain tissue. In some circumstances, such as epileptic seizures, both "hemodynamic" and "tissue" factors may be operative at the same time. The selective features of BBB changes are related to multiplicity of barrier systems residing in cerebral endothelium. These selective features are demonstrable during development and during reversibility of postichemic barrier disturbances. Intermittent openings of the barrier observed in chronic hypertension may lead to accumulation of extravasated serum proteins and be responsible for frequently observed edematous changes in this condition.