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.