Influence of blood-brain barrier opening to proteins on development of post-ischaemic brain injury.

The effect of the BBB opening to proteins on development of post-ischaemic brain injury was assessed in 32 cats subjected to one hour MCA occlusion. The CBF was measured by hydrogen clearance from electrodes inserted in the caudate and the cerebral cortex within the MCA territory. In 16 animals, a prevention of subsequent reactive hyperaemia was attempted by hypovolaemia, produced by withdrawal of blood just before the release of MCA occlusion. The hypovolaemia was successful in prevention of post-ischaemic hyperaemia in five out of eight cats sacrificed at 3 h and in six out of eight animals killed after 3 and 14 days. In cats sacrificed 3 h after release of MCA occlusion, ischaemic sites, associated with reactive hyperaemia, showed evidence of BBB breakdown to proteins and significantly more severe oedema than at the ischaemic sites without reactive hyperaemia, which otherwise failed to reveal leakage of EB tracer. In the cats sacrificed at 3 and 14 days, the ischaemic sites which showed reactive hyperaemia after release of MCA occlusion, revealed much more severe ischaemic brain tissue injury than was observed at the sites without reactive hyperaemia, which also did not show any EB leakage. The present study indicates that reactive hyperaemia, which follows release of major cerebral artery occlusion, may play a significant role in the breakdown of the BBB to proteins, and in increasing the severity of post-ischaemic oedema and of ischaemic brain tissue injury.