Extravasation of albumin in ischaemic brain oedema

Changes in brain water, sodium, potassium, and albumin contents and blood-brain barrier (BBB) permeability were determined between 1 hr and 42 days following occlusion of the middle cerebral artery in rats. Brain oedema was maximal 24 hrs, remained high for 3 days, and was resolved by 4 weeks. These changes in water content were accompanied by a parallel increase in sodium and decrease in potassium, however, the increase in sodium always exceeded the decrease in potassium so that there was a net gain in brain cations. BBB permeability to 3H-alpha-aminoisobutyric acid was normal for the first 4 hrs, but increased by 24 hr and returned to normal at 3 weeks. The time course for changes in brain albumin content was the same as that for BBB permeability and, at its greatest (3 days), the brain albumin was approximately 20% of the plasma albumin concentration. The relative contributions of the osmotic force produced by the increase in brain cations and the oncotic force produced by the increase in brain albumin to the observed change in water content were calculated. At all time points, the increase in brain cations accounted for nearly all of the observed brain oedema, while the increase in albumin played essentially no role in oedema development.