Regional brain uptake of noradrenaline following mechanical or osmotic opening of the blood-brain barrier.

The passage of noradrenaline from the cerebrovascular circulation into the brain (vessel walls and parenchyma) was studied quantitatively and regionally by a modification of Oldendorf's technique for determination of brain uptake index. Using 14C-ethanol as the highly diffusible internal standard, the index for noradrenaline varied between 2.7 and 4.5% in different regions, confirming the poor penetration of this neurotransmitter. The barrier was impaired transiently as evidenced by Evans blue extravasation, through osmotic opening by internal carotid injection of a hyperosmolar urea solution or mechanical disruption by a short-lasting elevation of the intracarotid hydrostatic pressure. This resulted in a 3-4-fold increase in the passage of noradrenaline from the circulation into the brain.